cargo-rail 0.27.0

//! Analyze and apply deterministic workspace dependency repairs.
//!
//! Implements resolution-based unification:
//! 1. Multi-target metadata for versions
//! 2. Manifest parsing for minimal features
//! 3. Intersection-based feature unification

use crate::cargo::{ManifestWriter, UnifyAnalyzer, UnifyReport};
use crate::commands::common::{UnifyOutputFormat, format_preview_list};
use crate::error::{RailError, RailResult};
use crate::mutation::{self, ExpectedMutation, MutationAction, MutationEffect, MutationRisk, MutationTrace};
use crate::progress;
use crate::workspace::WorkspaceContext;
use rscrypto::Sha256;
use std::collections::BTreeSet;
use std::path::{Path, PathBuf};

struct UnifyTextSink {
    buffer: Option<String>,
}

impl UnifyTextSink {
    fn new(capture: bool) -> Self {
        Self {
            buffer: capture.then_some(String::new()),
        }
    }

    fn push_line(&mut self, args: std::fmt::Arguments<'_>) {
        if let Some(ref mut buf) = self.buffer {
            buf.push_str(&args.to_string());
            buf.push('\n');
        } else {
            println!("{}", args);
        }
    }

    fn finish(self) -> Option<String> {
        self.buffer
    }
}

macro_rules! outln {
  ($sink:expr $(,)?) => {{
    $sink.push_line(format_args!(""));
  }};
  ($sink:expr, $($arg:tt)*) => {{
    $sink.push_line(format_args!($($arg)*));
  }};
}

fn write_output(content: &str, output_file: Option<&PathBuf>) -> RailResult<()> {
    use std::io::Write as _;

    let needs_trailing_newline = !content.ends_with('\n');
    match output_file {
        Some(path) => {
            let mut file = std::fs::OpenOptions::new()
                .create(true)
                .truncate(true)
                .write(true)
                .open(path)
                .map_err(|e| RailError::message(format!("failed to open '{}': {}", path.display(), e)))?;
            file.write_all(content.as_bytes())
                .map_err(|e| RailError::message(format!("failed to write '{}': {}", path.display(), e)))?;
            if needs_trailing_newline {
                file.write_all(b"\n")
                    .map_err(|e| RailError::message(format!("failed to write '{}': {}", path.display(), e)))?;
            }
            progress!("output: {}", path.display());
            Ok(())
        }
        None => {
            print!("{}", content);
            if needs_trailing_newline {
                println!();
            }
            Ok(())
        }
    }
}

fn format_quoted_list(values: &[impl AsRef<str>]) -> String {
    let mut out = String::with_capacity(values.iter().map(|v| v.as_ref().len()).sum::<usize>() + values.len() * 4 + 2);
    out.push('[');
    for (idx, value) in values.iter().enumerate() {
        if idx > 0 {
            out.push_str(", ");
        }
        out.push('"');
        out.push_str(value.as_ref());
        out.push('"');
    }
    out.push(']');
    out
}

fn dependency_section<'a>(dep_kind: &crate::cargo::DepKind, target: Option<&'a str>) -> std::borrow::Cow<'a, str> {
    use std::borrow::Cow;

    match (dep_kind, target) {
        (crate::cargo::DepKind::Dev, None) => Cow::Borrowed("[dev-dependencies]"),
        (crate::cargo::DepKind::Build, None) => Cow::Borrowed("[build-dependencies]"),
        (_, None) => Cow::Borrowed("[dependencies]"),
        (crate::cargo::DepKind::Dev, Some(t)) => Cow::Owned(format!("[target.'{}'.dev-dependencies]", t)),
        (crate::cargo::DepKind::Build, Some(t)) => Cow::Owned(format!("[target.'{}'.build-dependencies]", t)),
        (_, Some(t)) => Cow::Owned(format!("[target.'{}'.dependencies]", t)),
    }
}

fn mutation_targets(actions: &[MutationAction]) -> Vec<String> {
    actions
        .iter()
        .flat_map(|action| action.expected_mutations.iter())
        .map(|mutation| crate::utils::path_to_git_format(&mutation.path))
        .collect::<BTreeSet<_>>()
        .into_iter()
        .collect()
}

fn blocked_issue_lines(plan: &crate::cargo::UnificationPlan) -> Vec<String> {
    plan.issues
        .iter()
        .filter(|issue| issue.severity == crate::cargo::IssueSeverity::Error)
        .map(|issue| format!("{}: {}", issue.dep_name, issue.message))
        .collect()
}

fn changed_dependency_names(plan: &crate::cargo::UnificationPlan) -> Vec<String> {
    let mut names = BTreeSet::new();
    names.extend(plan.workspace_deps.iter().map(|dependency| dependency.name.to_string()));
    names.extend(
        plan.transitive_pins
            .iter()
            .map(|dependency| dependency.name.to_string()),
    );
    names.extend(
        plan.unused_deps
            .iter()
            .map(|dependency| dependency.dep_name.to_string()),
    );
    names.extend(
        plan.undeclared_features
            .iter()
            .map(|feature| feature.dep_name.to_string()),
    );
    for edit in plan.member_edits.values().flatten() {
        match edit {
            crate::cargo::MemberEdit::UseWorkspace { dep_name, .. }
            | crate::cargo::MemberEdit::RemoveDep { dep_name, .. }
            | crate::cargo::MemberEdit::AddFeatures { dep_name, .. } => {
                names.insert(dep_name.to_string());
            }
            crate::cargo::MemberEdit::RemoveFeature { .. }
            | crate::cargo::MemberEdit::EnforceMsrvInheritance
            | crate::cargo::MemberEdit::InheritPackageField { .. } => {}
        }
    }
    names.into_iter().collect()
}

fn write_compact_summary(
    sink: &mut UnifyTextSink,
    plan: &crate::cargo::UnificationPlan,
    msrv_write_needed: bool,
    has_changes: bool,
    actions: &[MutationAction],
) {
    let workspace_dep_names: Vec<String> = plan.workspace_deps.iter().map(|dep| dep.name.to_string()).collect();
    let nothing_changed = workspace_dep_names.is_empty()
        && plan.member_edit_count() == 0
        && plan.transitive_pins.is_empty()
        && !msrv_write_needed
        && plan.pruned_features.is_empty()
        && plan.unused_deps.is_empty();
    let blocked = blocked_issue_lines(plan);
    if !blocked.is_empty() {
        outln!(sink, "Blocked:");
        for line in blocked.iter().take(5) {
            outln!(sink, "  {}", line);
        }
        if blocked.len() > 5 {
            outln!(sink, "  ... +{} more", blocked.len() - 5);
        }
        outln!(sink, "Next: cargo rail unify --explain");
    } else if has_changes && !nothing_changed {
        let root_manifest_changed = !workspace_dep_names.is_empty()
            || !plan.transitive_pins.is_empty()
            || msrv_write_needed
            || plan.package_inheritance_edit_count() > 0;
        let manifests = plan.member_edits.len() + usize::from(root_manifest_changed);
        let dependency_names = changed_dependency_names(plan);
        outln!(sink, "Pending: {manifests} manifest(s).");
        if !dependency_names.is_empty() {
            outln!(sink, "Dependencies: {}", format_preview_list(&dependency_names, 8));
        }
        if crate::output::is_verbose() {
            let targets = mutation_targets(actions);
            outln!(
                sink,
                "Mutation paths ({}): {}",
                targets.len(),
                format_preview_list(&targets, 8)
            );
        }
        outln!(sink, "Next: cargo rail unify apply");
    } else {
        outln!(sink, "Dependencies are coherent.");
    }
}

fn decision_reasons_to_json(reasons: &[crate::cargo::UnifyDecisionReason]) -> Vec<serde_json::Value> {
    reasons
        .iter()
        .map(|reason| {
            serde_json::json!({
              "code": reason.code.as_str(),
              "summary": &*reason.summary,
              "features": reason.features.iter().map(|value| &**value).collect::<Vec<_>>(),
              "members": reason.members.iter().map(|value| &**value).collect::<Vec<_>>(),
              "borrowed_from": reason.borrowed_from.iter().map(|value| &**value).collect::<Vec<_>>(),
              "feature_paths": reason.feature_paths.iter().map(|path| serde_json::json!({
                "member": &*path.member,
                "alias": &*path.alias,
                "dependency_kind": path.dependency_kind.as_str(),
                "target": path.target.as_deref(),
                "features": path.features.iter().map(|feature| &**feature).collect::<Vec<_>>(),
                "default_features": path.default_features,
                "optional": path.optional,
              })).collect::<Vec<_>>(),
            })
        })
        .collect()
}

fn dependency_decisions_to_json(plan: &crate::cargo::UnificationPlan) -> Vec<serde_json::Value> {
    plan.dependency_decisions
        .iter()
        .map(|decision| {
            serde_json::json!({
              "dep_name": &*decision.dep_name,
              "subject": decision.subject.as_str(),
              "member": decision.member.as_deref(),
              "target": decision.target.as_deref(),
              "reasons": decision_reasons_to_json(&decision.reasons),
            })
        })
        .collect()
}

fn feature_reachability_to_json(plan: &crate::cargo::UnificationPlan) -> Vec<serde_json::Value> {
    plan.reachable_features
        .iter()
        .map(|feature| {
            serde_json::json!({
              "member": &*feature.crate_name,
              "feature": &*feature.feature_name,
              "root_kind": feature.root_kind,
              "path": feature.path.iter().map(|item| &**item).collect::<Vec<_>>(),
            })
        })
        .collect()
}

fn evidence_cache_to_json(plan: &crate::cargo::UnificationPlan) -> Vec<serde_json::Value> {
    plan.unused_deps
        .iter()
        .map(|unused| {
            serde_json::json!({
              "member": &*unused.member,
              "dependency": &*unused.dep_name,
              "hits": unused.proof.cache_hits,
              "misses": unused.proof.cache_misses,
              "miss_reasons": unused.proof.cache_miss_reasons.iter().map(|value| &**value).collect::<Vec<_>>(),
            })
        })
        .collect()
}

fn proof_certificates_to_json(plan: &crate::cargo::UnificationPlan, msrv_write_needed: bool) -> Vec<serde_json::Value> {
    let mut certificates =
        Vec::with_capacity(plan.unused_deps.len() + plan.pruned_features.len() + plan.undeclared_features.len());
    certificates.extend(plan.unused_deps.iter().map(|unused| {
        serde_json::json!({
          "schema_version": unused.proof.schema_version,
          "member": &*unused.member,
          "subject": {
            "kind": "dependency",
            "declaration": &*unused.dep_name,
            "package_ids": unused.proof.package_ids.iter().map(|value| &**value).collect::<Vec<_>>(),
            "crate_names": unused.proof.crate_names.iter().map(|value| &**value).collect::<Vec<_>>(),
            "dependency_kind": unused.kind.as_str(),
            "target": unused.target.as_deref(),
          },
          "decision": "remove",
          "evidence_source": unused.proof.evidence_source,
          "applicable_configurations": unused.proof.applicable_configurations,
          "complete_configurations": unused.proof.complete_configurations,
          "used_observations": unused.proof.used_observations,
          "unused_observations": unused.proof.unused_observations,
          "incomplete_observations": unused.proof.incomplete_observations,
          "uncertainties": unused.proof.uncertainties.iter().map(|value| &**value).collect::<Vec<_>>(),
        })
    }));
    certificates.extend(plan.pruned_features.iter().map(|feature| {
        serde_json::json!({
          "schema_version": 1,
          "member": &*feature.crate_name,
          "subject": { "kind": "feature", "declaration": &*feature.feature_name },
          "decision": "remove",
          "evidence_source": "feature_reachability",
          "roots_checked": [
            "published_api", "default", "resolved", "workspace_consumer",
            "source_cfg", "cargo_target_required", "preservation_policy"
          ],
          "declared_edges": feature.declared_edges.iter().map(|edge| &**edge).collect::<Vec<_>>(),
          "reachable_path": [],
          "package_visibility": "publish_false",
          "consumer_scope": "workspace",
          "uncertainties": [],
        })
    }));
    certificates.extend(plan.undeclared_features.iter().map(|feature| {
        serde_json::json!({
          "schema_version": 1,
          "member": &*feature.member,
          "subject": {
            "kind": "dependency_features",
            "declaration": &*feature.dep_name,
            "dependency_kind": feature.dep_kind.as_str(),
            "target": feature.target.as_deref(),
          },
          "decision": "add_features",
          "features": feature.undeclared_features.iter().map(|value| &**value).collect::<Vec<_>>(),
          "evidence_source": "standalone_compiler_causality",
          "borrowed_from": feature.borrowed_from.iter().map(|value| &**value).collect::<Vec<_>>(),
          "required_by": feature.required_by.iter().map(|value| &**value).collect::<Vec<_>>(),
          "uncertainties": [],
        })
    }));
    certificates.extend(plan.workspace_deps.iter().map(|dependency| {
        serde_json::json!({
          "schema_version": 1,
          "member": serde_json::Value::Null,
          "subject": {
            "kind": "workspace_dependency",
            "declaration": &*dependency.name,
            "package": dependency.package.as_deref(),
          },
          "decision": "unify",
          "evidence_source": "cargo_resolve_and_manifest_intersection",
          "version_requirement": dependency.version_req.to_string(),
          "features": dependency.features.iter().map(|feature| &**feature).collect::<Vec<_>>(),
          "default_features": dependency.default_features,
          "used_by": dependency.used_by.iter().map(|member| &**member).collect::<Vec<_>>(),
          "target": dependency.target.as_deref(),
          "path_dependency": dependency.path.is_some(),
          "uncertainties": [],
        })
    }));
    for (member, edits) in &plan.member_edits {
        certificates.extend(edits.iter().filter_map(|edit| match edit {
            crate::cargo::MemberEdit::UseWorkspace {
                dep_name,
                dep_kind,
                target,
                local_features,
                is_optional,
            } => Some(serde_json::json!({
              "schema_version": 1,
              "member": &**member,
              "subject": {
                "kind": "dependency_declaration",
                "declaration": &**dep_name,
                "dependency_kind": dep_kind.as_str(),
                "target": target.as_deref(),
              },
              "decision": "use_workspace",
              "evidence_source": "cargo_resolve_and_manifest_identity",
              "local_features": local_features.iter().map(|feature| &**feature).collect::<Vec<_>>(),
              "optional": is_optional,
              "uncertainties": [],
            })),
            crate::cargo::MemberEdit::EnforceMsrvInheritance => Some(serde_json::json!({
              "schema_version": 1,
              "member": &**member,
              "subject": { "kind": "package_msrv", "declaration": "package.rust-version" },
              "decision": "inherit_workspace",
              "evidence_source": "computed_workspace_msrv",
              "uncertainties": [],
            })),
            crate::cargo::MemberEdit::InheritPackageField { field } => Some(serde_json::json!({
              "schema_version": 1,
              "member": &**member,
              "subject": { "kind": "package_field", "declaration": format!("package.{field}") },
              "decision": "inherit_workspace",
              "evidence_source": "captured_semantic_manifest_equality",
              "uncertainties": [],
            })),
            crate::cargo::MemberEdit::RemoveDep { .. }
            | crate::cargo::MemberEdit::RemoveFeature { .. }
            | crate::cargo::MemberEdit::AddFeatures { .. } => None,
        }));
    }
    certificates.extend(plan.transitive_pins.iter().map(|dependency| {
        serde_json::json!({
          "schema_version": 1,
          "member": serde_json::Value::Null,
          "subject": { "kind": "transitive_dependency", "declaration": &*dependency.name },
          "decision": "pin",
          "evidence_source": "resolved_fragmented_feature_sets",
          "version": dependency.version.to_string(),
          "features": dependency.features.iter().map(|feature| &**feature).collect::<Vec<_>>(),
          "uncertainties": [],
        })
    }));
    if msrv_write_needed && let Some(msrv) = &plan.computed_msrv {
        certificates.push(serde_json::json!({
          "schema_version": 1,
          "member": serde_json::Value::Null,
          "subject": { "kind": "workspace_msrv", "declaration": "workspace.package.rust-version" },
          "decision": "write",
          "evidence_source": "resolved_dependency_msrv",
          "version": msrv.version.to_string(),
          "contributors": msrv.contributors,
          "uncertainties": [],
        }));
    }
    certificates.sort_by(|left, right| {
        left["member"]
            .as_str()
            .cmp(&right["member"].as_str())
            .then_with(|| left["subject"]["kind"].as_str().cmp(&right["subject"]["kind"].as_str()))
            .then_with(|| {
                left["subject"]["declaration"]
                    .as_str()
                    .cmp(&right["subject"]["declaration"].as_str())
            })
            .then_with(|| left.to_string().cmp(&right.to_string()))
    });
    certificates
}

fn proof_set_fingerprint(certificates: &[serde_json::Value]) -> String {
    let encoded = serde_json::Value::Array(certificates.to_vec()).to_string();
    sha256_fingerprint(encoded.as_bytes())
}

fn sha256_fingerprint(bytes: &[u8]) -> String {
    crate::instrumentation::record_hash(bytes.len());
    let digest = Sha256::digest(bytes);
    let mut fingerprint = String::with_capacity("sha256:".len() + digest.len() * 2);
    fingerprint.push_str("sha256:");
    for byte in digest {
        const HEX: &[u8; 16] = b"0123456789abcdef";
        fingerprint.push(char::from(HEX[usize::from(byte >> 4)]));
        fingerprint.push(char::from(HEX[usize::from(byte & 0x0f)]));
    }
    fingerprint
}

fn root_manifest_value(ctx: &WorkspaceContext) -> RailResult<serde_json::Value> {
    let manifest = ctx.snapshot()?.workspace_manifest()?;
    let text = std::str::from_utf8(manifest.bytes())
        .map_err(|_| RailError::message("workspace root Cargo.toml is not valid UTF-8"))?;
    toml_edit::de::from_str(text)
        .map_err(|error| RailError::message(format!("failed to parse workspace resolver: {error}")))
}

fn root_manifest_document(ctx: &WorkspaceContext) -> RailResult<toml_edit::DocumentMut> {
    let manifest = ctx.snapshot()?.workspace_manifest()?;
    let text = std::str::from_utf8(manifest.bytes())
        .map_err(|_| RailError::message("workspace root Cargo.toml is not valid UTF-8"))?;
    text.parse()
        .map_err(|error| RailError::message(format!("failed to parse workspace root Cargo.toml: {error}")))
}

fn coverage_views_to_json(coverage_views: &[crate::compiler::CoverageView]) -> RailResult<serde_json::Value> {
    let views = coverage_views
        .iter()
        .map(|view| {
            let (mode, selected) = match &view.features {
                crate::compiler::FeatureSelection::Default => ("default", Vec::new()),
                crate::compiler::FeatureSelection::DefaultWith(features) => ("default_with_selected", features.clone()),
                crate::compiler::FeatureSelection::NoDefaultFeatures => ("no_default_features", Vec::new()),
                crate::compiler::FeatureSelection::AllFeatures => ("all_features", Vec::new()),
                crate::compiler::FeatureSelection::Selected(features) => ("selected", features.clone()),
            };
            Ok(serde_json::json!({
              "id": view.identity()?,
              "target": view.target.as_str(),
              "features": {
                "mode": mode,
                "selected": selected,
              },
              "packages": view.packages,
              "cargo": {
                "program": "cargo",
                "args": view.cargo_arguments(),
              },
              "nextest": {
                "program": "cargo",
                "args": view.nextest_arguments(),
              },
            }))
        })
        .collect::<RailResult<Vec<_>>>()?;
    Ok(serde_json::json!({
      "schema_version": 1,
      "views": views,
    }))
}

fn package_inheritance_to_json(plan: &crate::cargo::UnificationPlan) -> serde_json::Value {
    let fields = plan
        .package_inheritance
        .iter()
        .map(|field| {
            serde_json::json!({
              "field": &*field.field,
              "inherited": field.inherited.iter().map(|member| &**member).collect::<Vec<_>>(),
              "planned": field.planned.iter().map(|member| &**member).collect::<Vec<_>>(),
              "local_overrides": field.local_overrides.iter().map(|member| &**member).collect::<Vec<_>>(),
              "missing": field.missing.iter().map(|member| &**member).collect::<Vec<_>>(),
              "retained_equivalent": field.retained_equivalent.iter().map(|member| &**member).collect::<Vec<_>>(),
              "retention_reason": field.retention_reason,
            })
        })
        .collect::<Vec<_>>();
    serde_json::json!({
      "schema_version": 1,
      "authority": "workspace.package",
      "fields": fields,
    })
}

fn msrv_to_json(
    ctx: &WorkspaceContext,
    plan: &crate::cargo::UnificationPlan,
    write_needed: bool,
) -> RailResult<serde_json::Value> {
    let snapshot = ctx.snapshot()?;
    let (rustc_release, rustc_channel) = tool_release_and_channel(snapshot.toolchain().rustc_verbose_version());
    let candidate_version = plan.computed_msrv.as_ref().map(|msrv| &msrv.version);
    let toolchain_constraint = msrv_toolchain_constraint_to_json(candidate_version, &rustc_release);
    let policy = match ctx.config() {
        Some(config) => serde_json::to_value(config.unify.msrv_policy)?,
        None => serde_json::to_value(crate::config::MsrvPolicy::default())?,
    };
    let candidate = plan.computed_msrv.as_ref().map(|msrv| {
        let source = match msrv.source_used {
            crate::cargo::MsrvSourceUsed::Deps => "dependencies",
            crate::cargo::MsrvSourceUsed::Workspace => "workspace",
            crate::cargo::MsrvSourceUsed::MaxWorkspace => "max_workspace",
            crate::cargo::MsrvSourceUsed::MaxDeps => "max_dependencies",
        };
        serde_json::json!({
          "version": msrv.version.to_string(),
          "source": source,
          "declared_workspace": msrv.workspace_msrv.as_ref().map(ToString::to_string),
          "dependency_floor": msrv.deps_msrv.as_ref().map(ToString::to_string),
          "dependency_evidence_count": msrv.deps_with_msrv,
          "contributors": msrv.contributors,
          "warning": msrv.warning,
        })
    });
    Ok(serde_json::json!({
      "schema_version": 1,
      "policy": policy,
      "candidate": candidate,
      "write_needed": write_needed,
      "selected_toolchain": {
        "rustc_release": rustc_release,
        "channel": rustc_channel,
        "host": snapshot.toolchain().host_target(),
        "fingerprint": snapshot.toolchain_fingerprint(),
      },
      "toolchain_constraint": toolchain_constraint,
      "compiler_probe": {
        "status": "not_run",
        "lowering_authorized": false,
        "required_scope": "all configured coverage views",
        "meaning": "the candidate is a manifest/dependency lower bound; validation requires builds under that compiler",
      },
    }))
}

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
enum MsrvToolchainConstraintStatus {
    Satisfied,
    Unsatisfied,
    Unknown,
    NotApplicable,
}

impl MsrvToolchainConstraintStatus {
    fn as_str(self) -> &'static str {
        match self {
            Self::Satisfied => "satisfied",
            Self::Unsatisfied => "unsatisfied",
            Self::Unknown => "unknown",
            Self::NotApplicable => "not_applicable",
        }
    }
}

fn normalized_rustc_release(release: &str) -> Option<semver::Version> {
    let release = semver::Version::parse(release).ok()?;
    Some(semver::Version::new(release.major, release.minor, release.patch))
}

fn msrv_toolchain_constraint(
    candidate: Option<&semver::Version>,
    rustc_release: &str,
) -> (MsrvToolchainConstraintStatus, Option<semver::Version>) {
    let Some(candidate) = candidate else {
        return (MsrvToolchainConstraintStatus::NotApplicable, None);
    };
    let Some(selected) = normalized_rustc_release(rustc_release) else {
        return (MsrvToolchainConstraintStatus::Unknown, None);
    };
    let required = semver::Version::new(candidate.major, candidate.minor, candidate.patch);
    let status = if selected >= required {
        MsrvToolchainConstraintStatus::Satisfied
    } else {
        MsrvToolchainConstraintStatus::Unsatisfied
    };
    (status, Some(selected))
}

fn msrv_toolchain_constraint_to_json(candidate: Option<&semver::Version>, rustc_release: &str) -> serde_json::Value {
    let (status, selected) = msrv_toolchain_constraint(candidate, rustc_release);
    let meaning = match status {
        MsrvToolchainConstraintStatus::Satisfied => {
            "the captured compiler is at or above the candidate; this does not validate the candidate compiler"
        }
        MsrvToolchainConstraintStatus::Unsatisfied => "the captured compiler is older than the candidate",
        MsrvToolchainConstraintStatus::Unknown => "the captured compiler release could not be parsed",
        MsrvToolchainConstraintStatus::NotApplicable => "no MSRV candidate was computed",
    };
    serde_json::json!({
      "status": status.as_str(),
      "required": candidate.map(ToString::to_string),
      "selected": selected.map(|version| version.to_string()),
      "evidence_source": "captured_rustc_identity",
      "meaning": meaning,
    })
}

fn resolver_diagnostic(root: &serde_json::Value) -> (String, String) {
    let explicit = root
        .get("workspace")
        .and_then(|workspace| workspace.get("resolver"))
        .or_else(|| root.get("package").and_then(|package| package.get("resolver")));
    if let Some(resolver) =
        explicit.and_then(|value| value.as_str().map(str::to_string).or_else(|| Some(value.to_string())))
    {
        return (resolver.trim_matches('"').to_string(), "manifest".to_string());
    }
    let Some(package) = root.get("package") else {
        return ("1".to_string(), "virtual-workspace default".to_string());
    };
    let edition = package
        .get("edition")
        .and_then(serde_json::Value::as_str)
        .unwrap_or("2015");
    let resolver = match edition {
        "2024" => "3",
        "2021" => "2",
        _ => "1",
    };
    (resolver.to_string(), format!("inferred from edition {edition}"))
}

fn cargo_source_overrides(root: &serde_json::Value, cargo_config: &serde_json::Value) -> Vec<String> {
    let mut overrides = Vec::new();
    if let Some(patches) = root.get("patch").and_then(serde_json::Value::as_object) {
        for (source, entries) in patches {
            let source = if crate::cargo::resolution::credential_bearing_url(source) {
                "<credential-bearing-url>"
            } else {
                source
            };
            if let Some(entries) = entries.as_object() {
                overrides.extend(entries.keys().map(|name| format!("patch.{source}.{name}")));
            }
        }
    }
    if let Some(replacements) = root.get("replace").and_then(serde_json::Value::as_object) {
        overrides.extend(replacements.keys().map(|name| format!("replace.{name}")));
    }
    if let Some(sources) = cargo_config.get("source").and_then(serde_json::Value::as_object) {
        for (name, source) in sources {
            if source.as_object().is_some_and(|source| {
                ["replace-with", "registry", "local-registry", "directory"]
                    .iter()
                    .any(|key| source.contains_key(*key))
            }) {
                overrides.push(format!("source.{name}"));
            }
        }
    }
    overrides.sort();
    overrides.dedup();
    overrides
}

fn unify_policy_overrides(ctx: &WorkspaceContext) -> RailResult<Vec<String>> {
    let actual = serde_json::to_value(ctx.config().map(|config| &config.unify).cloned().unwrap_or_default())?;
    let defaults = serde_json::to_value(crate::config::UnifyConfig::default())?;
    let Some(actual) = actual.as_object() else {
        return Err(RailError::message("effective unify configuration is not an object"));
    };
    let Some(defaults) = defaults.as_object() else {
        return Err(RailError::message("default unify configuration is not an object"));
    };
    Ok(actual
        .iter()
        .filter(|(key, value)| defaults.get(*key) != Some(*value))
        .map(|(key, _)| key.clone())
        .collect())
}

fn tool_release_and_channel(verbose_version: &str) -> (String, &'static str) {
    let release = verbose_version
        .lines()
        .find_map(|line| line.strip_prefix("release: "))
        .or_else(|| {
            verbose_version
                .lines()
                .next()
                .and_then(|line| line.split_whitespace().nth(1))
        })
        .unwrap_or("unknown")
        .to_string();
    let channel = if release.contains("nightly") {
        "nightly"
    } else if release.contains("beta") {
        "beta"
    } else if release == "unknown" {
        "unknown"
    } else {
        "stable"
    };
    (release, channel)
}

/// Inspect the exact Cargo resolution domains used by dependency unification.
pub fn run_unify_doctor(ctx: &WorkspaceContext, format: UnifyOutputFormat) -> RailResult<()> {
    let snapshot = ctx.snapshot()?;
    let root = root_manifest_value(ctx)?;
    let (resolver, resolver_source) = resolver_diagnostic(&root);
    let (cargo_version, cargo_channel) = tool_release_and_channel(snapshot.toolchain().cargo_verbose_version());
    let cargo_overrides = cargo_source_overrides(&root, snapshot.cargo_config().effective_file_settings());
    let policy_overrides = unify_policy_overrides(ctx)?;
    let ambiguous_aliases = ctx.graph().ambiguous_aliases();

    // MultiTargetMetadata is deliberately backed by the same exact ResolutionView
    // cache as planning. Doctor observes that model instead of reconstructing it.
    let metadata = ctx.multi_target_metadata()?;
    let host = snapshot.toolchain().host_target();
    let metadata_targets = metadata.targets();
    let compiler_targets = ctx
        .config()
        .map(|config| config.unify.effective_compiler_targets(&metadata_targets))
        .unwrap_or_else(|| metadata_targets.clone());
    let mut target_domains = Vec::with_capacity(metadata_targets.len());
    for target in metadata_targets {
        let resolved_nodes = metadata
            .get(target)
            .and_then(|metadata| metadata.resolve.as_ref())
            .map_or(0, |resolve| resolve.nodes.len());
        target_domains.push(serde_json::json!({
          "target": target,
          "role": if target == "default" { "unfiltered" } else if target == host { "host" } else { "target" },
          "feature_mode": "default",
          "resolved_node_count": resolved_nodes,
        }));
    }

    let aliases = ambiguous_aliases
        .iter()
        .map(|alias| {
            serde_json::json!({
              "member": alias.member_name,
              "member_package_id": alias.member_id.to_string(),
              "alias": alias.alias,
              "candidates": alias.candidates.iter().map(|candidate| serde_json::json!({
                "package": candidate.package_name,
                "package_id": candidate.package_id.to_string(),
                "domains": candidate.domains,
              })).collect::<Vec<_>>(),
            })
        })
        .collect::<Vec<_>>();
    let (recommendation_code, recommendation) = if !aliases.is_empty() {
        (
            "disambiguate_aliases",
            "make each dependency alias resolve to one PackageId per workspace member and selected target",
        )
    } else if resolver == "1" {
        (
            "upgrade_resolver",
            "set workspace.resolver to the resolver required by the workspace edition before unifying features",
        )
    } else if !cargo_overrides.is_empty() {
        (
            "review_source_overrides",
            "review active Cargo source overrides, then run cargo rail unify --check --explain",
        )
    } else {
        ("check", "run cargo rail unify --check --explain")
    };

    if format.is_json() {
        let value = crate::output::machine_json_envelope(
            "unify",
            "doctor",
            "success",
            0,
            serde_json::json!({
              "cargo": { "version": cargo_version, "channel": cargo_channel },
              "resolver": { "version": resolver, "source": resolver_source },
              "feature_mode": { "packages": "workspace", "features": "default" },
              "effective_overrides": {
                "cargo_sources": cargo_overrides,
                "unify_policy": policy_overrides,
              },
              "target_domains": target_domains,
              "compiler_evidence_targets": compiler_targets,
              "ambiguous_aliases": aliases,
              "recommended_action": {
                "code": recommendation_code,
                "message": recommendation,
              },
            }),
        );
        let rendered = serde_json::to_string_pretty(&value)?;
        return write_output(&rendered, None);
    }

    let mut rendered = String::with_capacity(512);
    rendered.push_str("unify doctor\n\ncargo: ");
    rendered.push_str(&cargo_version);
    rendered.push_str(" (");
    rendered.push_str(cargo_channel);
    rendered.push_str(")\nresolver: ");
    rendered.push_str(&resolver);
    rendered.push_str(" (");
    rendered.push_str(&resolver_source);
    rendered.push_str(")\nfeatures: workspace/default\ntarget domains: ");
    rendered.push_str(&target_domains.len().to_string());
    rendered.push('\n');
    for target in &target_domains {
        rendered.push_str("  ");
        rendered.push_str(target["target"].as_str().unwrap_or("unknown"));
        rendered.push_str(" (");
        rendered.push_str(target["role"].as_str().unwrap_or("target"));
        rendered.push_str(", ");
        rendered.push_str(&target["resolved_node_count"].as_u64().unwrap_or(0).to_string());
        rendered.push_str(" resolved nodes)\n");
    }
    rendered.push_str("compiler evidence targets: ");
    rendered.push_str(&format_preview_list(&compiler_targets, 8));
    rendered.push('\n');
    rendered.push_str("cargo source overrides: ");
    rendered.push_str(&format_preview_list(&cargo_overrides, 8));
    rendered.push_str("\nunify policy overrides: ");
    rendered.push_str(&format_preview_list(&policy_overrides, 8));
    rendered.push_str("\nambiguous aliases: ");
    rendered.push_str(&aliases.len().to_string());
    rendered.push('\n');
    for alias in &aliases {
        rendered.push_str("  ");
        rendered.push_str(alias["member"].as_str().unwrap_or("unknown"));
        rendered.push(':');
        rendered.push_str(alias["alias"].as_str().unwrap_or("unknown"));
        rendered.push_str(" -> ");
        rendered.push_str(&alias["candidates"].as_array().map_or(0, Vec::len).to_string());
        rendered.push_str(" candidates\n");
    }
    rendered.push_str("recommended: ");
    rendered.push_str(recommendation);
    rendered.push('\n');
    write_output(&rendered, None)
}

/// Prepared options for dependency-coherence check mode.
#[derive(Debug)]
#[doc(hidden)]
pub struct UnifyAnalyzeOptions<'a> {
    pub(crate) check: bool,
    pub(crate) show_diff: bool,
    pub(crate) explain: bool,
    pub(crate) format: UnifyOutputFormat,
    pub(crate) output: Option<&'a PathBuf>,
    pub(crate) backup: bool,
    pub(crate) no_report: bool,
    pub(crate) report_path: Option<&'a PathBuf>,
}

/// Analyze workspace dependencies (check mode)
pub fn run_unify_analyze(ctx: &WorkspaceContext, options: UnifyAnalyzeOptions<'_>) -> RailResult<()> {
    let UnifyAnalyzeOptions {
        check,
        show_diff,
        explain,
        format,
        output,
        backup,
        no_report,
        report_path,
    } = options;
    ctx.snapshot()?;
    let json = format.is_json();

    // JSON mode enables structured error output and suppresses progress

    // Create analyzer (config comes from rail.toml via ctx)
    let analyzer = UnifyAnalyzer::new(ctx)?;

    // Run analysis
    ctx.validate_snapshot_unchanged()?;
    let plan = analyzer.analyze()?;
    let coverage_views = analyzer.coverage_views()?;
    ctx.validate_snapshot_unchanged()?;
    let msrv_write_needed = if let Some(msrv) = plan.computed_msrv.as_ref() {
        workspace_msrv_write_needed(ctx, &msrv.version)?
    } else {
        false
    };

    let has_changes = plan.has_planned_changes(msrv_write_needed);
    let should_backup =
        has_changes && (backup || !crate::backup::BackupManager::new(ctx.workspace_root()).has_backups());
    let (actions, risks, trace) =
        build_unify_mutation_parts(ctx, &plan, msrv_write_needed, should_backup, no_report, report_path)?;

    // JSON output mode (but still honor exit codes)
    if json {
        let coverage = coverage_views_to_json(&coverage_views)?;
        let msrv = msrv_to_json(ctx, &plan, msrv_write_needed)?;
        let proof_certificates = proof_certificates_to_json(&plan, msrv_write_needed);
        let proof_fingerprint = proof_set_fingerprint(&proof_certificates);
        let mutation_plan = if ctx.has_git() {
            Some(mutation::build_plan(
                ctx,
                "unify",
                actions.clone(),
                risks.clone(),
                trace.clone(),
            )?)
        } else {
            None
        };

        let mut canonical_actions = actions;
        canonical_actions.sort_by(|a, b| {
            a.code
                .cmp(&b.code)
                .then_with(|| a.target.cmp(&b.target))
                .then_with(|| a.detail.cmp(&b.detail))
        });
        let mut reason_codes: Vec<String> = mutation_plan
            .as_ref()
            .map(|plan| {
                plan.trace
                    .iter()
                    .map(|t| t.code.clone())
                    .chain(plan.risks.iter().map(|r| r.code.clone()))
                    .collect()
            })
            .unwrap_or_else(|| {
                trace
                    .iter()
                    .map(|t| t.code.clone())
                    .chain(risks.iter().map(|r| r.code.clone()))
                    .collect()
            });
        reason_codes.sort();
        reason_codes.dedup();

        let payload = serde_json::json!({
          "command": "unify",
          "check": true,
          "msrv_write_needed": msrv_write_needed,
          "has_changes": has_changes,
          "workspace_deps": plan.workspace_deps.iter().map(|d| {
            let features: Vec<&str> = d.features.iter().map(|f| &**f).collect();
            serde_json::json!({
              "name": &*d.name,
              "package": d.package.as_deref(),
              "version": d.version_req,
              "features": features,
            })
          }).collect::<Vec<_>>(),
          "summary": {
            "workspace_deps_count": plan.workspace_deps.len(),
            "member_edits_count": plan.member_edit_count(),
            "package_fields_inherited": plan.package_inheritance_edit_count(),
            "members_affected": plan.member_edits.len(),
            "transitive_pins_count": plan.transitive_pins.len(),
            "duplicates_unified": plan.duplicates_cleaned.len(),
            "dead_features_pruned": plan.pruned_features.len(),
            "optional_features_detected": plan.optional_features.len(),
            "version_mismatches": plan.version_mismatches.len(),
            "unused_deps": plan.unused_deps.len(),
          },
          "has_blocking_issues": plan.has_blocking_issues(),
          "issues": plan.issues.iter().map(|i| serde_json::json!({
            "kind": format!("{:?}", i.kind),
            "dep_name": &*i.dep_name,
            "severity": format!("{:?}", i.severity),
            "message": &*i.message,
          })).collect::<Vec<_>>(),
          "dependency_decisions": dependency_decisions_to_json(&plan),
          "feature_reachability": feature_reachability_to_json(&plan),
          "package_inheritance": package_inheritance_to_json(&plan),
          "coverage": coverage,
          "msrv": msrv,
          "evidence_cache": evidence_cache_to_json(&plan),
          "proof_fingerprint": proof_fingerprint,
          "proof_certificates": proof_certificates,
          "action_plan": canonical_actions,
          "reason_codes": reason_codes,
          "mutation_plan_available": mutation_plan.is_some(),
          "mutation_plan": mutation_plan,
        });

        let exit_code = if plan.has_blocking_issues() {
            2
        } else if has_changes && check {
            1
        } else {
            0
        };
        let result = if plan.has_blocking_issues() {
            "failed"
        } else if has_changes {
            "pending_changes"
        } else {
            "success"
        };
        let output_json = crate::output::machine_json_envelope(
            "unify",
            if check { "check" } else { "preview" },
            result,
            exit_code,
            payload,
        );
        let rendered =
            serde_json::to_string_pretty(&output_json).map_err(|e| RailError::message(format!("JSON error: {}", e)))?;
        write_output(&rendered, output)?;

        if plan.has_blocking_issues() {
            return Err(RailError::message("blocking issues prevent unification"));
        }
        if has_changes && check {
            return Err(RailError::CheckHasPendingChanges);
        }
        return Ok(());
    }

    let mut sink = UnifyTextSink::new(output.is_some());

    // Default output stays terse; detailed reasoning belongs behind --explain or JSON.
    write_compact_summary(&mut sink, &plan, msrv_write_needed, has_changes, &actions);

    // Show explain output if requested
    if explain {
        display_explain(&mut sink, &plan);
    }

    // Show diff if requested
    if show_diff && has_changes {
        outln!(sink);
        outln!(sink, "planned changes:");
        outln!(sink);

        // Show MSRV update first (workspace manifest)
        if let Some(msrv) = plan.computed_msrv.as_ref()
            && msrv_write_needed
        {
            outln!(sink, "[workspace.package]:");
            outln!(
                sink,
                "  rust-version = \"{}.{}.{}\"",
                msrv.version.major,
                msrv.version.minor,
                msrv.version.patch
            );
            outln!(sink);
        }

        // Show workspace deps that will be added
        if !plan.workspace_deps.is_empty() || !plan.transitive_pins.is_empty() {
            outln!(sink, "[workspace.dependencies]:");
            for dep in &plan.workspace_deps {
                outln!(sink, "  + {} = \"{}\"", dep.name, dep.version_req);
                if !dep.features.is_empty() {
                    let mut features = dep.features.clone();
                    features.sort();
                    outln!(sink, "      features = {}", format_quoted_list(&features));
                }
            }

            // Show transitive pins (also written to workspace.dependencies)
            for pin in &plan.transitive_pins {
                outln!(sink, "  + {} = \"{}\"  # transitive pin", pin.name, pin.version);
                if !pin.features.is_empty() {
                    let mut features = pin.features.clone();
                    features.sort();
                    outln!(sink, "      features = {}", format_quoted_list(&features));
                }
            }
            outln!(sink);
        }

        // Show member edits
        let mut members: Vec<_> = plan.member_edits.keys().collect();
        members.sort();
        for member in members {
            let edits = &plan.member_edits[member];
            if edits.is_empty() {
                continue;
            }
            let path = plan
                .member_paths
                .get(member)
                .map(|p| p.display().to_string())
                .unwrap_or_else(|| member.to_string());
            outln!(sink, "{}:", path);
            for edit in edits {
                match edit {
                    crate::cargo::MemberEdit::UseWorkspace {
                        dep_name,
                        dep_kind,
                        target,
                        local_features,
                        is_optional,
                    } => {
                        let section = dependency_section(dep_kind, target.as_deref());
                        let mut line = String::with_capacity(64 + section.len() + dep_name.len());
                        line.push_str("  ");
                        line.push_str(&section);
                        line.push(' ');
                        line.push_str(dep_name);
                        line.push_str(" -> workspace = true");
                        if !local_features.is_empty() {
                            let mut features = local_features.clone();
                            features.sort();
                            line.push_str(", features = ");
                            line.push_str(&format_quoted_list(&features));
                        }
                        if *is_optional {
                            line.push_str(", optional = true");
                        }
                        outln!(sink, "{}", line);
                    }
                    crate::cargo::MemberEdit::RemoveDep {
                        dep_name,
                        dep_kind,
                        target,
                    } => {
                        let section = dependency_section(dep_kind, target.as_deref());
                        outln!(sink, "  {} {} -> REMOVE (unused)", section, dep_name);
                    }
                    crate::cargo::MemberEdit::RemoveFeature { feature_name } => {
                        outln!(sink, "  [features] {} -> REMOVE (dead/empty)", feature_name);
                    }
                    crate::cargo::MemberEdit::AddFeatures {
                        dep_name,
                        dep_kind,
                        target,
                        features_to_add,
                    } => {
                        let section = dependency_section(dep_kind, target.as_deref());
                        let mut sorted_features = features_to_add.clone();
                        sorted_features.sort();
                        outln!(
                            sink,
                            "  {} {} -> ADD features {}",
                            section,
                            dep_name,
                            format_quoted_list(&sorted_features)
                        );
                    }
                    crate::cargo::MemberEdit::EnforceMsrvInheritance => {
                        outln!(sink, "  [package] rust-version = {{ workspace = true }}");
                    }
                    crate::cargo::MemberEdit::InheritPackageField { field } => {
                        outln!(sink, "  [package] {} = {{ workspace = true }}", field);
                    }
                }
            }
            outln!(sink);
        }
    }

    // Final message and exit code
    if plan.has_blocking_issues() {
        eprintln!();
        crate::error!("blocking issues prevent unification");
        if let Some(content) = sink.finish() {
            write_output(&content, output)?;
        }
        return Err(RailError::message("blocking issues prevent unification"));
    } else if has_changes && check {
        if let Some(content) = sink.finish() {
            write_output(&content, output)?;
        }
        return Err(RailError::CheckHasPendingChanges);
    }

    if let Some(content) = sink.finish() {
        write_output(&content, output)?;
    }

    Ok(())
}

/// Execute dependency unification
struct ManifestTransaction {
    originals: Vec<(std::path::PathBuf, OriginalFileState)>,
}

enum OriginalFileState {
    File(Vec<u8>),
    Absent,
}

#[derive(Debug, Default)]
struct ResolvedGraphSnapshot {
    facts: std::collections::BTreeMap<String, BTreeSet<String>>,
    adjacency: std::collections::BTreeMap<String, BTreeSet<String>>,
}

#[derive(Debug)]
struct VerifiedGraphDelta {
    added: usize,
    removed: usize,
    fingerprint: String,
    facts: Vec<String>,
    post_mutation_lock_fingerprint: String,
    post_mutation_metadata: std::sync::Arc<cargo_metadata::Metadata>,
}

#[derive(Debug)]
struct VerifiedCoverageSet {
    identities: Vec<String>,
    fingerprint: String,
}

fn resolved_graph_snapshot(metadata: &cargo_metadata::Metadata) -> RailResult<ResolvedGraphSnapshot> {
    let workspace_ids: std::collections::HashSet<_> = metadata.workspace_members.iter().collect();
    let workspace_root = metadata.workspace_root.as_std_path();
    let mut package_by_id = std::collections::HashMap::with_capacity(metadata.packages.len());
    let mut snapshot = ResolvedGraphSnapshot::default();
    for package in &metadata.packages {
        let identity = if workspace_ids.contains(&package.id) {
            format!("workspace:{}@{}", package.name, package.version)
        } else if let Some(source) = &package.source {
            format!("{}#{}@{}", source, package.name, package.version)
        } else {
            let package_dir = package
                .manifest_path
                .parent()
                .map(|path| path.as_std_path())
                .unwrap_or_else(|| package.manifest_path.as_std_path());
            let portable_path = relative_path(workspace_root, package_dir)
                .map(|path| crate::utils::path_to_git_format(&path))
                .unwrap_or_else(|| crate::utils::file_fingerprint(package.manifest_path.as_std_path()));
            format!("path:{portable_path}#{}@{}", package.name, package.version)
        };
        package_by_id.insert(package.id.to_string(), (identity.clone(), package.name.to_string()));
        snapshot.facts.insert(
            format!("package|{identity}"),
            BTreeSet::from([package.name.to_string()]),
        );
    }

    let resolve = metadata
        .resolve
        .as_ref()
        .ok_or_else(|| RailError::message("Cargo returned no resolve graph".to_string()))?;
    for node in &resolve.nodes {
        let Some((from_identity, from_name)) = package_by_id.get(&node.id.to_string()) else {
            continue;
        };
        for feature in &node.features {
            snapshot.facts.insert(
                format!("feature|{from_identity}|{feature}"),
                BTreeSet::from([from_name.clone()]),
            );
        }
        for dependency in &node.deps {
            let Some((to_identity, to_name)) = package_by_id.get(&dependency.pkg.to_string()) else {
                continue;
            };
            let mut domains: Vec<_> = dependency
                .dep_kinds
                .iter()
                .map(|domain| {
                    format!(
                        "{:?}:{}",
                        domain.kind,
                        domain.target.as_ref().map(ToString::to_string).unwrap_or_default()
                    )
                })
                .collect();
            domains.sort();
            snapshot.facts.insert(
                format!(
                    "edge|{from_identity}|{}|{to_identity}|{}",
                    dependency.name,
                    domains.join(",")
                ),
                BTreeSet::from([from_name.clone(), to_name.clone(), dependency.name.clone()]),
            );
            snapshot
                .adjacency
                .entry(from_name.clone())
                .or_default()
                .insert(to_name.clone());
        }
    }
    Ok(snapshot)
}

fn relative_path(base: &Path, target: &Path) -> Option<PathBuf> {
    use std::path::Component;

    let base: Vec<_> = base.components().collect();
    let target: Vec<_> = target.components().collect();
    let common = base
        .iter()
        .zip(&target)
        .take_while(|(left, right)| left == right)
        .count();
    if common == 0 {
        return None;
    }
    let mut relative = PathBuf::new();
    for component in &base[common..] {
        if matches!(component, Component::Normal(_)) {
            relative.push("..");
        }
    }
    for component in &target[common..] {
        relative.push(component.as_os_str());
    }
    Some(relative)
}

fn authorized_graph_names(plan: &crate::cargo::UnificationPlan) -> BTreeSet<String> {
    let mut names = BTreeSet::new();
    names.extend(plan.workspace_deps.iter().map(|dependency| dependency.name.to_string()));
    names.extend(
        plan.workspace_deps
            .iter()
            .filter_map(|dependency| dependency.package.as_deref().map(str::to_string)),
    );
    names.extend(
        plan.transitive_pins
            .iter()
            .map(|dependency| dependency.name.to_string()),
    );
    for dependency in &plan.unused_deps {
        names.insert(dependency.member.to_string());
        names.insert(dependency.dep_name.to_string());
    }
    for feature in &plan.undeclared_features {
        names.insert(feature.member.to_string());
        names.insert(feature.dep_name.to_string());
    }
    for feature in &plan.pruned_features {
        names.insert(feature.crate_name.to_string());
        for edge in &feature.declared_edges {
            let dependency = edge
                .strip_prefix("dep:")
                .unwrap_or(edge)
                .split(['/', '?'])
                .next()
                .unwrap_or_default();
            if !dependency.is_empty() {
                names.insert(dependency.to_string());
            }
        }
    }
    names
}

fn graph_name_closure(
    roots: &BTreeSet<String>,
    before: &ResolvedGraphSnapshot,
    after: &ResolvedGraphSnapshot,
) -> BTreeSet<String> {
    let mut closure = roots.clone();
    let mut pending: Vec<_> = roots.iter().cloned().collect();
    while let Some(name) = pending.pop() {
        for next in before
            .adjacency
            .get(&name)
            .into_iter()
            .chain(after.adjacency.get(&name))
            .flatten()
        {
            if closure.insert(next.clone()) {
                pending.push(next.clone());
            }
        }
    }
    closure
}

impl ManifestTransaction {
    fn capture(
        ctx: &WorkspaceContext,
        plan: &crate::cargo::UnificationPlan,
        msrv_write_needed: bool,
        additional_paths: &[PathBuf],
    ) -> RailResult<Self> {
        let mut paths = std::collections::BTreeSet::new();
        if !plan.workspace_deps.is_empty() || !plan.transitive_pins.is_empty() || msrv_write_needed {
            paths.insert(ctx.workspace_root().join("Cargo.toml"));
        }
        for member in plan.member_edits.keys() {
            if let Some(path) = plan.member_paths.get(member) {
                paths.insert(path.clone());
            }
        }
        if !plan.transitive_pins.is_empty() {
            paths.insert(transitive_pins_host_manifest_path(ctx)?);
        }
        let lockfile_path = ctx.workspace_root().join("Cargo.lock");
        paths.insert(lockfile_path);
        paths.extend(additional_paths.iter().cloned());
        let mut originals = Vec::with_capacity(paths.len());
        for path in paths {
            let state = match std::fs::symlink_metadata(&path) {
                Ok(metadata) if metadata.file_type().is_file() => {
                    OriginalFileState::File(std::fs::read(&path).map_err(|error| {
                        RailError::message(format!("capturing {} before unify apply: {error}", path.display()))
                    })?)
                }
                Ok(_) => {
                    return Err(RailError::message(format!(
                        "unify mutation target '{}' is not a regular file",
                        path.display()
                    )));
                }
                Err(error) if error.kind() == std::io::ErrorKind::NotFound => OriginalFileState::Absent,
                Err(error) => {
                    return Err(RailError::message(format!(
                        "inspecting {} before unify apply: {error}",
                        path.display()
                    )));
                }
            };
            originals.push((path, state));
        }
        Ok(Self { originals })
    }

    fn restore(&self) -> RailResult<()> {
        for (path, state) in &self.originals {
            match state {
                OriginalFileState::File(content) => {
                    crate::utils::write_file_atomic(path, content).map_err(|error| {
                        RailError::message(format!(
                            "restoring {} after failed unify apply: {error}",
                            path.display()
                        ))
                    })?
                }
                OriginalFileState::Absent => match std::fs::symlink_metadata(path) {
                    Ok(metadata) if metadata.file_type().is_file() => std::fs::remove_file(path).map_err(|error| {
                        RailError::message(format!(
                            "removing transaction-created {} after failed unify apply: {error}",
                            path.display()
                        ))
                    })?,
                    Ok(_) => {
                        return Err(RailError::message(format!(
                            "refusing to remove non-file transaction target '{}' during rollback",
                            path.display()
                        )));
                    }
                    Err(error)
                        if matches!(
                            error.kind(),
                            std::io::ErrorKind::NotFound | std::io::ErrorKind::NotADirectory
                        ) => {}
                    Err(error) => {
                        return Err(RailError::message(format!(
                            "inspecting transaction-created {} during rollback: {error}",
                            path.display()
                        )));
                    }
                },
            }
        }
        Ok(())
    }
}

fn verify_applied_unify_graph(
    ctx: &WorkspaceContext,
    plan: &crate::cargo::UnificationPlan,
) -> RailResult<VerifiedGraphDelta> {
    let snapshot = ctx.snapshot()?;
    let target_metadata = ctx.multi_target_metadata()?;
    let targets = target_metadata.targets();
    let mut verified_feature_edits = std::collections::BTreeSet::new();
    let authorized_names = authorized_graph_names(plan);
    let mut delta_lines = BTreeSet::new();
    let mut added = 0usize;
    let mut removed = 0usize;
    let mut post_mutation_metadata = None;
    let lockfile_path = ctx.workspace_root().join("Cargo.lock");
    let mut post_mutation_lock_fingerprint = None;
    for target in targets {
        let before_metadata = target_metadata
            .metadata_for_target(target)
            .ok_or_else(|| RailError::message(format!("missing pre-edit metadata for target `{target}`")))?;
        let before = resolved_graph_snapshot(before_metadata)?;
        let mut command = cargo_metadata::MetadataCommand::new();
        command
            .cargo_path(std::path::PathBuf::from(snapshot.toolchain().cargo_program()))
            .current_dir(snapshot.cargo_current_dir())
            .manifest_path(ctx.workspace_root().join("Cargo.toml"));
        let mut options = Vec::new();
        if post_mutation_lock_fingerprint.is_some() {
            options.push(String::from("--locked"));
        }
        if target != "default" {
            options.extend([String::from("--filter-platform"), target.to_string()]);
        }
        if !options.is_empty() {
            command.other_options(options);
        }
        if let Some(expected) = post_mutation_lock_fingerprint.as_deref() {
            snapshot.validate_post_mutation_environment_unchanged()?;
            validate_post_mutation_lockfile(&lockfile_path, expected)?;
        } else {
            snapshot.validate_post_mutation_resolution_inputs_unchanged()?;
        }
        crate::instrumentation::record_cargo_metadata_load(target != "default");
        let metadata = command.exec().map_err(|error| {
            if snapshot.cargo_config().has_credential_capability() {
                RailError::with_help(
                    format!("resolving post-edit metadata for target '{target}' failed while credential capabilities were active"),
                    "run cargo metadata directly for provider diagnostics; cargo-rail suppresses credential-provider output",
                )
            } else {
                RailError::message(format!("resolving post-edit metadata for target `{target}`: {error}"))
            }
        })?;
        let metadata = std::sync::Arc::new(crate::workspace::capture_metadata_paths(metadata)?);
        snapshot.validate_post_mutation_environment_unchanged()?;
        let current_lock_fingerprint = lockfile_content_fingerprint(&lockfile_path)?;
        if let Some(expected) = post_mutation_lock_fingerprint.as_deref() {
            if current_lock_fingerprint != expected {
                return Err(RailError::message(format!(
                    "Cargo.lock changed while resolving post-mutation target `{target}`"
                )));
            }
        } else {
            post_mutation_lock_fingerprint = Some(current_lock_fingerprint);
        }
        post_mutation_metadata.get_or_insert_with(|| std::sync::Arc::clone(&metadata));
        let after = resolved_graph_snapshot(&metadata)?;
        let closure = graph_name_closure(&authorized_names, &before, &after);
        for (fact, participants) in after.facts.iter().filter(|(fact, _)| !before.facts.contains_key(*fact)) {
            if participants.is_disjoint(&closure) {
                return Err(RailError::message(format!(
                    "unplanned graph addition on `{target}` outside the authorized dependency closure: {fact}"
                )));
            }
            added += 1;
            delta_lines.insert(format!("{target}|+|{fact}"));
        }
        for (fact, participants) in before.facts.iter().filter(|(fact, _)| !after.facts.contains_key(*fact)) {
            if participants.is_disjoint(&closure) {
                return Err(RailError::message(format!(
                    "unplanned graph removal on `{target}` outside the authorized dependency closure: {fact}"
                )));
            }
            removed += 1;
            delta_lines.insert(format!("{target}|-|{fact}"));
        }
        let resolve = metadata
            .resolve
            .as_ref()
            .ok_or_else(|| RailError::message(format!("Cargo returned no resolve graph for target `{target}`")))?;

        for unused in &plan.unused_deps {
            let Some(package) = metadata
                .packages
                .iter()
                .find(|package| package.name.as_ref() == &*unused.member)
            else {
                return Err(RailError::message(format!(
                    "workspace member `{}` disappeared after removing `{}`",
                    unused.member, unused.dep_name
                )));
            };
            let declaration_remains = package.dependencies.iter().any(|dependency| {
                let declaration_name = dependency.rename.as_deref().unwrap_or_else(|| dependency.name.as_ref());
                let kind_matches = matches!(
                    (unused.kind, dependency.kind),
                    (crate::cargo::DepKind::Normal, cargo_metadata::DependencyKind::Normal)
                        | (crate::cargo::DepKind::Dev, cargo_metadata::DependencyKind::Development)
                        | (crate::cargo::DepKind::Build, cargo_metadata::DependencyKind::Build)
                );
                declaration_name == &*unused.dep_name
                    && kind_matches
                    && dependency.target.as_ref().map(ToString::to_string).as_deref() == unused.target.as_deref()
            });
            if declaration_remains {
                return Err(RailError::message(format!(
                    "removed {} dependency `{}` still exists for `{}` in target scope {:?}",
                    unused.kind.as_str(),
                    unused.dep_name,
                    unused.member,
                    unused.target
                )));
            }
        }

        for undeclared in &plan.undeclared_features {
            let Some(package) = metadata
                .packages
                .iter()
                .find(|package| package.name.as_ref() == &*undeclared.member)
            else {
                continue;
            };
            let Some(member_node) = resolve.nodes.iter().find(|node| node.id == package.id) else {
                continue;
            };
            let crate_name = undeclared.dep_name.replace('-', "_");
            let Some(dependency) = member_node.deps.iter().find(|dependency| dependency.name == crate_name) else {
                continue;
            };
            let Some(dependency_node) = resolve.nodes.iter().find(|node| node.id == dependency.pkg) else {
                continue;
            };
            for feature in &undeclared.undeclared_features {
                if dependency_node
                    .features
                    .iter()
                    .any(|resolved| resolved.as_str() == &**feature)
                {
                    verified_feature_edits.insert((
                        undeclared.member.to_string(),
                        undeclared.dep_name.to_string(),
                        feature.to_string(),
                    ));
                }
            }
        }
    }

    for undeclared in &plan.undeclared_features {
        for feature in &undeclared.undeclared_features {
            let key = (
                undeclared.member.to_string(),
                undeclared.dep_name.to_string(),
                feature.to_string(),
            );
            if !verified_feature_edits.contains(&key) {
                return Err(RailError::message(format!(
                    "feature `{}/{}` did not resolve for `{}` after the planned edit",
                    undeclared.dep_name, feature, undeclared.member
                )));
            }
        }
    }
    let facts: Vec<_> = delta_lines.into_iter().collect();
    let mut encoded = String::new();
    for line in &facts {
        encoded.push_str(line);
        encoded.push('\n');
    }
    Ok(VerifiedGraphDelta {
        added,
        removed,
        fingerprint: sha256_fingerprint(encoded.as_bytes()),
        facts,
        post_mutation_lock_fingerprint: post_mutation_lock_fingerprint.ok_or_else(|| {
            RailError::message("unify graph verification produced no post-mutation lockfile identity")
        })?,
        post_mutation_metadata: post_mutation_metadata
            .ok_or_else(|| RailError::message("unify graph verification had no configured target views"))?,
    })
}

fn validate_post_mutation_lockfile(path: &Path, expected: &str) -> RailResult<()> {
    let actual = lockfile_content_fingerprint(path)?;
    if actual == expected {
        return Ok(());
    }
    Err(RailError::with_help(
        format!("Cargo.lock changed after the authorized graph refresh (expected {expected}, found {actual})"),
        "retry after lockfile writers have stopped",
    ))
}

fn lockfile_content_fingerprint(path: &Path) -> RailResult<String> {
    let bytes = std::fs::read(path)
        .map_err(|error| RailError::message(format!("reading post-mutation lockfile '{}': {error}", path.display())))?;
    Ok(sha256_fingerprint(&bytes))
}

fn verify_applied_coverage_views(
    ctx: &WorkspaceContext,
    coverage_views: &[crate::compiler::CoverageView],
    post_mutation_metadata: &cargo_metadata::Metadata,
    post_mutation_lock_fingerprint: &str,
) -> RailResult<VerifiedCoverageSet> {
    let snapshot = ctx.snapshot()?;
    let lockfile_path = ctx.workspace_root().join("Cargo.lock");
    let mut identities = Vec::with_capacity(coverage_views.len());
    for view in coverage_views {
        snapshot.validate_post_mutation_environment_unchanged()?;
        validate_post_mutation_lockfile(&lockfile_path, post_mutation_lock_fingerprint)?;
        let identity = view.identity()?;
        let request = crate::cargo::resolution::coverage_resolution_request(view, post_mutation_metadata)
            .map_err(|error| RailError::message(format!("reconstructing {identity}: {error}")))?;
        snapshot
            .post_mutation_resolution_view(request, post_mutation_metadata)
            .map_err(|error| RailError::message(format!("resolving {identity}: {error}")))?;
        snapshot.validate_post_mutation_environment_unchanged()?;
        validate_post_mutation_lockfile(&lockfile_path, post_mutation_lock_fingerprint)?;
        identities.push(identity);
    }
    identities.sort();
    if identities.windows(2).any(|pair| pair[0] == pair[1]) {
        return Err(RailError::message(
            "post-mutation coverage verification received duplicate view identities",
        ));
    }
    let mut encoded = identities.join("\n");
    encoded.push('\n');
    Ok(VerifiedCoverageSet {
        identities,
        fingerprint: sha256_fingerprint(encoded.as_bytes()),
    })
}

fn display_unify_apply_summary(
    plan: &crate::cargo::UnificationPlan,
    features_fixed: usize,
    crates_fixed: usize,
    backup_id: Option<&str>,
) {
    println!(
        "\nunified {} dependencies across {} members",
        plan.workspace_deps.len(),
        plan.member_edits.len()
    );
    if !plan.transitive_pins.is_empty() {
        println!("  {} transitives pinned", plan.transitive_pins.len());
    }
    if !plan.duplicates_cleaned.is_empty() {
        println!("  {} duplicates resolved", plan.duplicates_cleaned.len());
    }
    if !plan.pruned_features.is_empty() {
        println!("  {} unreachable private features pruned", plan.pruned_features.len());
    }
    if !plan.optional_features.is_empty() {
        println!(
            "  {} optional features detected (user-facing, preserved)",
            plan.optional_features.len()
        );
    }
    if features_fixed > 0 {
        println!(
            "  {} undeclared features fixed across {} crates",
            features_fixed, crates_fixed
        );
    }
    let package_fields_inherited = plan.package_inheritance_edit_count();
    if package_fields_inherited > 0 {
        println!("  {} package fields inherited", package_fields_inherited);
    }
    if let Some(msrv) = &plan.computed_msrv {
        use crate::cargo::MsrvSourceUsed;
        let source_desc = match msrv.source_used {
            MsrvSourceUsed::Deps | MsrvSourceUsed::MaxDeps => format!(
                "from deps: {}",
                msrv.contributors.first().map_or("unknown", AsRef::as_ref)
            ),
            MsrvSourceUsed::Workspace => "preserved from workspace".to_string(),
            MsrvSourceUsed::MaxWorkspace => "from workspace (higher than deps)".to_string(),
        };
        println!(
            "  rust-version = {}.{}.{} ({})",
            msrv.version.major, msrv.version.minor, msrv.version.patch, source_desc
        );
    }
    println!("\nnext: cargo nextest run -P commit --locked --config-file .config/nextest.toml");
    if let Some(backup_id) = backup_id {
        println!("undo: cargo rail unify undo  (backup: {backup_id})");
    }
}

/// Apply a verified dependency-unification plan transactionally.
pub fn run_unify_apply(
    ctx: &WorkspaceContext,
    backup: bool,
    no_report: bool,
    report_path: Option<std::path::PathBuf>,
    plan_path: Option<std::path::PathBuf>,
    format: UnifyOutputFormat,
) -> RailResult<()> {
    ctx.snapshot()?;
    use crate::backup::{BackupManager, BackupMetadata};
    use std::path::PathBuf;

    let json = format.is_json();

    // Create analyzer (config comes from rail.toml via ctx)
    let analyzer = UnifyAnalyzer::new(ctx)?;

    ctx.validate_snapshot_unchanged()?;
    let plan = analyzer.analyze()?;
    let coverage_views = analyzer.coverage_views()?;
    ctx.validate_snapshot_unchanged()?;
    let msrv_write_needed = if let Some(msrv) = plan.computed_msrv.as_ref() {
        workspace_msrv_write_needed(ctx, &msrv.version)?
    } else {
        false
    };
    let proof_certificates = proof_certificates_to_json(&plan, msrv_write_needed);
    let proof_fingerprint = proof_set_fingerprint(&proof_certificates);

    // Check for blockers
    if plan.has_blocking_issues() {
        crate::error!("blocking issues prevent unification:");
        for issue in &plan.issues {
            if issue.severity == crate::cargo::IssueSeverity::Error {
                eprintln!("  {}: {}", issue.dep_name, issue.message);
            }
        }
        return Err(crate::error::RailError::message("blocking issues prevent unification"));
    }

    if !plan.has_planned_changes(msrv_write_needed) {
        if json {
            let output = crate::output::machine_json_envelope(
                "unify",
                "apply",
                "unchanged",
                0,
                serde_json::json!({
                  "dependencies": 0,
                  "members": 0,
                  "portable": false,
                }),
            );
            println!("{}", serde_json::to_string_pretty(&output)?);
        } else {
            println!("nothing to unify");
        }
        return Ok(());
    }

    let backup_manager = BackupManager::new(ctx.workspace_root());
    let is_first_run = !backup_manager.has_backups();
    let should_backup = backup || is_first_run;
    let expected_mutation_plan = build_unify_mutation_plan(
        ctx,
        &plan,
        msrv_write_needed,
        should_backup,
        no_report,
        report_path.as_ref(),
    )?;
    let mutation_plan = if let Some(path) = plan_path.as_ref() {
        let from_file = mutation::read_plan_file(path)?;
        if from_file.contract_version != mutation::MUTATION_CONTRACT_VERSION {
            return Err(RailError::with_help(
                format!(
                    "unsupported mutation plan contract version: {} (expected {})",
                    from_file.contract_version,
                    mutation::MUTATION_CONTRACT_VERSION
                ),
                "regenerate the plan using the current cargo-rail version".to_string(),
            ));
        }
        if !from_file.operation_id.starts_with("unify-") {
            return Err(RailError::with_help(
                format!("plan '{}' is not a unify plan", path.display()),
                "use a plan generated from 'cargo rail unify --check -f json'".to_string(),
            ));
        }
        mutation::validate_pre_apply_with_allowed_paths(ctx, &from_file, std::slice::from_ref(path))?;
        mutation::validate_requested_operation(&from_file, &expected_mutation_plan)?;
        from_file
    } else {
        mutation::validate_pre_apply(ctx, &expected_mutation_plan)?;
        expected_mutation_plan
    };
    let plan_receipt = mutation::write_receipt(
        ctx.workspace_root(),
        "unify",
        "plan",
        "planned",
        mutation_plan.clone(),
        vec![
            MutationTrace::new("UNIFY_PLAN_CREATED", "created deterministic unify mutation plan"),
            MutationTrace::new(
                "UNIFY_PROOF_SET_BOUND",
                format!("bound portable proof set {proof_fingerprint}"),
            ),
        ],
    )?;
    progress!("receipt: {}", plan_receipt.display());

    // Create backup if requested or first run
    let mut created_backup_id: Option<String> = None;

    if should_backup {
        if is_first_run && !backup {
            progress!("creating backup (first run)...");
        } else {
            progress!("creating backup...");
        }

        // Estimate: root Cargo.toml + one per member with edits
        let mut files_to_backup = Vec::with_capacity(1 + plan.member_edits.len());
        if !plan.workspace_deps.is_empty() || !plan.transitive_pins.is_empty() || msrv_write_needed {
            files_to_backup.push(PathBuf::from("Cargo.toml"));
        }
        if ctx.workspace_root().join("Cargo.lock").is_file() {
            files_to_backup.push(PathBuf::from("Cargo.lock"));
        }

        // Transitive pins may also modify the configured host's Cargo.toml.
        if !plan.transitive_pins.is_empty() {
            let host_path = transitive_pins_host_manifest_path(ctx)?;
            if let Ok(rel_path) = host_path.strip_prefix(ctx.workspace_root()) {
                // Avoid duplicating root Cargo.toml when host is root.
                if rel_path != std::path::Path::new("Cargo.toml") {
                    files_to_backup.push(rel_path.to_path_buf());
                }
            }
        }

        for member_name in plan.member_edits.keys() {
            if let Some(manifest_path) = plan.member_paths.get(member_name)
                && let Ok(rel_path) = manifest_path.strip_prefix(ctx.workspace_root())
            {
                files_to_backup.push(rel_path.to_path_buf());
            }
        }

        let metadata = BackupMetadata::new("cargo rail unify");
        let max_backups = ctx.config().map(|c| c.unify.max_backups).unwrap_or(3);
        let backup_id = backup_manager.create_backup(&files_to_backup, metadata, max_backups)?;
        progress!("backup: {}", backup_id);
        created_backup_id = Some(backup_id);
    }

    let report_output_path = unify_report_output_path(ctx, &plan, no_report, report_path.as_deref())?;
    ctx.validate_snapshot_unchanged()?;
    let manifest_transaction =
        ManifestTransaction::capture(ctx, &plan, msrv_write_needed, report_output_path.as_slice())?;
    ctx.validate_snapshot_unchanged()?;
    let writer = ManifestWriter::new();
    let msrv_warning = plan.computed_msrv.as_ref().and_then(|msrv| msrv.warning.clone());

    let apply_result = (|| -> RailResult<(VerifiedGraphDelta, VerifiedCoverageSet, Option<PathBuf>)> {
        if !plan.workspace_deps.is_empty() {
            progress!("writing [workspace.dependencies]...");
            writer.write_workspace_deps(&ctx.workspace_root().join("Cargo.toml"), &plan.workspace_deps)?;
        }

        progress!("updating {} members...", plan.member_edits.len());
        let mut member_edits = plan.member_edits.iter().collect::<Vec<_>>();
        member_edits.sort_unstable_by_key(|(member, _)| *member);
        for (member_name, edits) in member_edits {
            let member_path = plan
                .member_paths
                .get(member_name)
                .ok_or_else(|| crate::error::RailError::message(format!("member path not found: {}", member_name)))?;

            for edit in edits {
                match edit {
                    crate::cargo::MemberEdit::UseWorkspace {
                        dep_name,
                        dep_kind,
                        target,
                        local_features,
                        is_optional,
                    } => {
                        writer.update_member(
                            member_path,
                            dep_name,
                            *dep_kind,
                            target.as_deref(),
                            if local_features.is_empty() {
                                None
                            } else {
                                Some(local_features.as_slice())
                            },
                            *is_optional,
                        )?;
                    }
                    crate::cargo::MemberEdit::RemoveDep {
                        dep_name,
                        dep_kind,
                        target,
                    } => {
                        writer.remove_dep(member_path, dep_name, *dep_kind, target.as_deref())?;
                    }
                    crate::cargo::MemberEdit::RemoveFeature { feature_name } => {
                        writer.remove_feature(member_path, feature_name)?;
                    }
                    crate::cargo::MemberEdit::AddFeatures {
                        dep_name,
                        dep_kind,
                        target,
                        features_to_add,
                    } => {
                        writer.add_features(member_path, dep_name, *dep_kind, target.as_deref(), features_to_add)?;
                    }
                    crate::cargo::MemberEdit::EnforceMsrvInheritance => {
                        writer.enforce_member_msrv_inheritance(member_path)?;
                    }
                    crate::cargo::MemberEdit::InheritPackageField { field } => {
                        writer.inherit_member_package_field(member_path, field)?;
                    }
                }
            }
        }

        if !plan.transitive_pins.is_empty() {
            progress!("pinning {} transitives...", plan.transitive_pins.len());

            // Add transitive deps to [workspace.dependencies] first
            // This is required before we can reference them with `workspace = true`
            progress!("  adding to [workspace.dependencies]...");
            writer.write_transitive_workspace_deps(&ctx.workspace_root().join("Cargo.toml"), &plan.transitive_pins)?;

            // Add to host's [dev-dependencies] with workspace = true
            let host_path = transitive_pins_host_manifest_path(ctx)?;
            let host_dir = host_path.parent().unwrap_or(&host_path);
            let relative_path = host_dir.strip_prefix(ctx.workspace_root()).unwrap_or(host_dir);
            if relative_path != std::path::Path::new("") && host_path != ctx.workspace_root().join("Cargo.toml") {
                progress!("  host: {}", relative_path.display());
            }
            writer.add_transitive_pins(&host_path, &plan.transitive_pins)?;
        }

        if let Some(ref msrv) = plan.computed_msrv {
            // Show warning if workspace mode has compatibility issues
            if let Some(ref warning) = msrv.warning
                && !json
            {
                crate::warn!("{}", warning);
            }
            if msrv_write_needed {
                progress!(
                    "writing rust-version = \"{}.{}.{}\"...",
                    msrv.version.major,
                    msrv.version.minor,
                    msrv.version.patch
                );
                writer.write_workspace_msrv(&ctx.workspace_root().join("Cargo.toml"), &msrv.version)?;
            }
        }

        progress!("verifying planned Cargo graph...");
        let graph_delta = verify_applied_unify_graph(ctx, &plan)
            .map_err(|error| RailError::message(format!("unify graph verification failed: {error}")))?;
        progress!(
            "  Authorized graph delta: {} addition(s), {} removal(s), {}",
            graph_delta.added,
            graph_delta.removed,
            graph_delta.fingerprint
        );

        progress!("verifying {} captured coverage views...", coverage_views.len());
        let coverage_verification = verify_applied_coverage_views(
            ctx,
            &coverage_views,
            graph_delta.post_mutation_metadata.as_ref(),
            &graph_delta.post_mutation_lock_fingerprint,
        )
        .map_err(|error| RailError::message(format!("unify coverage verification failed: {error}")))?;
        progress!(
            "  Verified {} coverage views: {}",
            coverage_verification.identities.len(),
            coverage_verification.fingerprint
        );

        let repaired_members: BTreeSet<_> = plan
            .member_edits
            .iter()
            .filter(|(_, edits)| {
                edits
                    .iter()
                    .any(|edit| matches!(edit, crate::cargo::MemberEdit::AddFeatures { .. }))
            })
            .map(|(member, _)| member.as_ref())
            .collect();
        if !repaired_members.is_empty() {
            progress!("verifying standalone feature repairs...");
            for member in repaired_members {
                crate::compiler::verify_standalone_member(ctx.workspace_root(), member)
                    .map_err(|error| RailError::message(format!("unify standalone verification failed: {error}")))?;
            }
        }

        if let Some(path) = &report_output_path {
            let revalidated = unify_report_output_path(ctx, &plan, no_report, report_path.as_deref())?;
            if revalidated.as_ref() != Some(path) {
                return Err(RailError::message(format!(
                    "unify report path changed after transaction capture (expected '{}', found '{}')",
                    path.display(),
                    revalidated
                        .as_deref()
                        .map_or_else(|| "disabled".to_string(), |current| current.display().to_string())
                )));
            }
            UnifyReport::write_to_file(&plan, path)?;
            progress!("report: {}", path.display());
        }
        // The captured fingerprint already binds existing dirt; this final check must reject only changes introduced
        // outside the transaction. Commands that prohibit a dirty starting state do not pass this allowance.
        let allowed_existing_paths: Vec<_> = mutation_plan
            .pre_apply
            .changed_paths
            .iter()
            .cloned()
            .chain(plan_path.iter().cloned())
            .collect();
        mutation::validate_changed_paths_with_allowed_paths(ctx, &mutation_plan, &allowed_existing_paths)?;
        Ok((graph_delta, coverage_verification, report_output_path.clone()))
    })();
    let (graph_delta, coverage_verification, written_report_path) = match apply_result {
        Ok(applied) => applied,
        Err(error) => {
            manifest_transaction.restore().map_err(|rollback| {
                RailError::message(format!("unify apply failed: {error}; rollback also failed: {rollback}"))
            })?;
            return Err(RailError::with_help(
                format!("unify apply failed: {error}"),
                "all authorized manifests, Cargo.lock, and report output were restored; resolve the failure and regenerate the plan",
            ));
        }
    };

    // Count undeclared feature fixes
    let features_fixed: usize = plan
        .member_edits
        .values()
        .flat_map(|edits| edits.iter())
        .filter_map(|e| match e {
            crate::cargo::MemberEdit::AddFeatures { features_to_add, .. } => Some(features_to_add.len()),
            _ => None,
        })
        .sum();
    let crates_fixed = plan
        .member_edits
        .values()
        .filter(|edits| {
            edits
                .iter()
                .any(|e| matches!(e, crate::cargo::MemberEdit::AddFeatures { .. }))
        })
        .count();

    let apply_receipt_result = mutation::write_receipt(
        ctx.workspace_root(),
        "unify",
        "apply",
        "applied",
        mutation_plan,
        vec![
            MutationTrace::new("UNIFY_APPLY_STARTED", "started applying unify plan"),
            MutationTrace::new(
                "UNIFY_GRAPH_DELTA_VERIFIED",
                format!(
                    "authorized graph delta: {} addition(s), {} removal(s), {}; lockfile {}",
                    graph_delta.added,
                    graph_delta.removed,
                    graph_delta.fingerprint,
                    graph_delta.post_mutation_lock_fingerprint
                ),
            ),
            MutationTrace::new(
                "UNIFY_COVERAGE_VIEWS_VERIFIED",
                format!(
                    "verified {} captured coverage view(s): {}",
                    coverage_verification.identities.len(),
                    coverage_verification.fingerprint
                ),
            ),
            MutationTrace::new(
                "UNIFY_PROOF_SET_BOUND",
                format!("applied portable proof set {proof_fingerprint}"),
            ),
            MutationTrace::new("UNIFY_APPLY_COMPLETED", "completed unify apply"),
        ],
    );
    let apply_receipt = match apply_receipt_result {
        Ok(path) => path,
        Err(error) => {
            manifest_transaction.restore().map_err(|rollback| {
                RailError::message(format!(
                    "writing the unify apply receipt failed: {error}; rollback also failed: {rollback}"
                ))
            })?;
            return Err(RailError::with_help(
                format!("writing the unify apply receipt failed: {error}"),
                "all authorized manifests, Cargo.lock, and report output were restored; resolve the receipt storage failure and retry",
            ));
        }
    };
    progress!("receipt: {}", apply_receipt.display());

    if !json {
        display_unify_apply_summary(&plan, features_fixed, crates_fixed, created_backup_id.as_deref());
    }

    if json {
        let warnings = msrv_warning.into_iter().collect::<Vec<_>>();
        let output = crate::output::machine_json_envelope(
            "unify",
            "apply",
            "applied",
            0,
            serde_json::json!({
              "dependencies": plan.workspace_deps.len(),
              "members": plan.member_edits.len(),
              "package_fields_inherited": plan.package_inheritance_edit_count(),
              "transitives_pinned": plan.transitive_pins.len(),
              "duplicates_resolved": plan.duplicates_cleaned.len(),
              "features_pruned": plan.pruned_features.len(),
              "optional_features_preserved": plan.optional_features.len(),
              "undeclared_features_fixed": features_fixed,
              "backup_id": created_backup_id,
              "report_path": written_report_path,
              "plan_receipt": plan_receipt,
              "apply_receipt": apply_receipt,
              "graph_delta": {
                "added_facts": graph_delta.added,
                "removed_facts": graph_delta.removed,
                "fingerprint": graph_delta.fingerprint,
                "lockfile_fingerprint": graph_delta.post_mutation_lock_fingerprint,
                "facts": graph_delta.facts,
              },
              "coverage_verification": {
                "schema_version": 1,
                "verified_views": coverage_verification.identities.len(),
                "identities": coverage_verification.identities,
                "fingerprint": coverage_verification.fingerprint,
              },
              "proof_fingerprint": proof_fingerprint,
              "warnings": warnings,
            }),
        );
        println!("{}", serde_json::to_string_pretty(&output)?);
    }

    Ok(())
}

/// Restore a previous state from backup
pub fn run_unify_undo(
    workspace_root: &std::path::Path,
    list: bool,
    backup_id: Option<String>,
    format: crate::commands::common::TextJsonOutputFormat,
) -> RailResult<()> {
    use crate::backup::BackupManager;

    let backup_manager = BackupManager::new(workspace_root);

    if list {
        let backups = backup_manager.list_backups()?;

        if format.is_json() {
            let output = crate::output::machine_json_envelope(
                "unify",
                "undo_list",
                "success",
                0,
                serde_json::json!({
                    "backups": backups.iter().enumerate().map(|(index, backup)| serde_json::json!({
                        "id": backup.id,
                        "latest": index == 0,
                        "timestamp": backup.metadata.timestamp,
                        "files": backup.metadata.files_modified,
                    })).collect::<Vec<_>>(),
                }),
            );
            println!("{}", serde_json::to_string_pretty(&output)?);
            return Ok(());
        }

        if backups.is_empty() {
            println!("no backups found");
            return Ok(());
        }

        println!("backups:\n");
        for (i, backup) in backups.iter().enumerate() {
            let marker = if i == 0 { " (latest)" } else { "" };
            println!("  {}{}", backup.id, marker);
            println!("    {}", backup.metadata.timestamp);
            println!("    {} files", backup.metadata.files_modified.len());
        }

        println!("\nrestore with: cargo rail unify undo [--backup-id <id>]");
        return Ok(());
    }

    let target_backup_id = if let Some(id) = backup_id {
        id
    } else {
        match backup_manager.get_latest_backup()? {
            Some(backup) => backup.id,
            None => {
                return Err(crate::error::RailError::with_help(
                    "no backups found",
                    "run 'cargo rail unify undo --list' to see available backups",
                ));
            }
        }
    };

    backup_manager.restore_backup(&target_backup_id)?;

    if format.is_json() {
        let output = crate::output::machine_json_envelope(
            "unify",
            "undo",
            "restored",
            0,
            serde_json::json!({ "backup_id": target_backup_id }),
        );
        println!("{}", serde_json::to_string_pretty(&output)?);
    } else {
        println!("Restored backup {target_backup_id}.");
    }

    Ok(())
}

/// Display detailed explanation of unification decisions
fn display_explain(sink: &mut UnifyTextSink, plan: &crate::cargo::UnificationPlan) {
    use std::collections::BTreeMap;

    outln!(sink);
    outln!(sink, "=== Explanation ===");
    outln!(sink);

    if !plan.package_inheritance.is_empty() {
        outln!(sink, "Package inheritance:");
        outln!(sink);
        for field in &plan.package_inheritance {
            outln!(sink, "  {}", field.field);
            if !field.planned.is_empty() {
                outln!(sink, "    inherit: {}", format_preview_list(&field.planned, 10));
            }
            if !field.local_overrides.is_empty() {
                outln!(
                    sink,
                    "    local overrides: {}",
                    format_preview_list(&field.local_overrides, 10)
                );
            }
            if !field.missing.is_empty() {
                outln!(sink, "    missing: {}", format_preview_list(&field.missing, 10));
            }
            if !field.retained_equivalent.is_empty() {
                outln!(
                    sink,
                    "    retained ({}): {}",
                    field.retention_reason.unwrap_or("domain-owned"),
                    format_preview_list(&field.retained_equivalent, 10)
                );
            }
        }
        outln!(sink);
    }

    if !plan.dependency_decisions.is_empty() {
        outln!(sink, "Dependency decisions:");
        outln!(sink);
        for decision in &plan.dependency_decisions {
            match (&decision.member, &decision.target) {
                (Some(member), Some(target)) => outln!(
                    sink,
                    "  {} [{}:{} @ {}]",
                    decision.dep_name,
                    decision.subject.as_str(),
                    member,
                    target
                ),
                (Some(member), None) => outln!(
                    sink,
                    "  {} [{}:{}]",
                    decision.dep_name,
                    decision.subject.as_str(),
                    member
                ),
                (None, _) => outln!(sink, "  {} [{}]", decision.dep_name, decision.subject.as_str()),
            }
            for reason in &decision.reasons {
                outln!(sink, "    - {}: {}", reason.code.as_str(), reason.summary);
                if !reason.features.is_empty() {
                    outln!(sink, "      features: {}", format_preview_list(&reason.features, 10));
                }
                if !reason.members.is_empty() {
                    outln!(sink, "      members: {}", format_preview_list(&reason.members, 10));
                }
                if !reason.borrowed_from.is_empty() {
                    outln!(
                        sink,
                        "      borrowed from: {}",
                        format_preview_list(&reason.borrowed_from, 10)
                    );
                }
                for path in &reason.feature_paths {
                    outln!(
                        sink,
                        "      path: {}:{} [{}{}] features={} default-features={} optional={}",
                        path.member,
                        path.alias,
                        path.dependency_kind.as_str(),
                        path.target
                            .as_deref()
                            .map(|target| format!(" @ {target}"))
                            .unwrap_or_default(),
                        format_preview_list(&path.features, 10),
                        path.default_features,
                        path.optional,
                    );
                }
            }
            outln!(sink);
        }
    }

    // Explain unused deps being removed
    if !plan.unused_deps.is_empty() {
        outln!(sink, "Unused dependencies flagged for removal:");
        outln!(sink);
        for unused in &plan.unused_deps {
            outln!(sink, "  {} in {}", unused.dep_name, unused.member);
            outln!(sink, "    reason: {:?}", unused.reason);
            outln!(
                sink,
                "    proof: {}/{} applicable configurations complete; {} unused; {} used; {} incomplete",
                unused.proof.complete_configurations,
                unused.proof.applicable_configurations,
                unused.proof.unused_observations,
                unused.proof.used_observations,
                unused.proof.incomplete_observations
            );
            outln!(
                sink,
                "    cache: {} hit; {} miss{}{}",
                unused.proof.cache_hits,
                unused.proof.cache_misses,
                if unused.proof.cache_misses == 1 { "" } else { "es" },
                if unused.proof.cache_miss_reasons.is_empty() {
                    String::new()
                } else {
                    format!(" ({})", unused.proof.cache_miss_reasons.join(", "))
                }
            );
            outln!(sink);
        }
    }

    if !plan.reachable_features.is_empty() {
        outln!(sink, "Feature reachability:");
        outln!(sink);
        for feature in &plan.reachable_features {
            outln!(
                sink,
                "  {} in {}: {} ({})",
                feature.feature_name,
                feature.crate_name,
                feature.path.join(" -> "),
                feature.root_kind
            );
        }
        outln!(sink);
    }

    // Explain pruned features
    if !plan.pruned_features.is_empty() {
        outln!(sink, "Dead features pruned:");
        outln!(sink);
        for pruned in &plan.pruned_features {
            outln!(sink, "  [features].{} in {}", pruned.feature_name, pruned.crate_name);
            outln!(sink, "    reason: unreachable from every feature root");
            if !pruned.declared_edges.is_empty() {
                outln!(sink, "    removed edges: {}", pruned.declared_edges.join(", "));
            }
            outln!(sink);
        }
    }

    // Explain issues/blockers
    if !plan.issues.is_empty() {
        outln!(sink, "Issues detected:");
        outln!(sink);

        // Group by severity
        let mut by_severity: BTreeMap<String, Vec<_>> = BTreeMap::new();
        for issue in &plan.issues {
            let severity = format!("{:?}", issue.severity);
            by_severity.entry(severity).or_default().push(issue);
        }

        for (severity, issues) in &by_severity {
            outln!(sink, "  {} ({}):", severity, issues.len());
            for issue in issues {
                outln!(sink, "    {}: {}", issue.dep_name, issue.message);
            }
            outln!(sink);
        }
    }

    if !plan.undeclared_features.is_empty() {
        outln!(sink, "Undeclared feature causality:");
        outln!(sink);
        for uf in &plan.undeclared_features {
            outln!(sink, "  {} in {}", uf.dep_name, uf.member);
            outln!(sink, "    undeclared: [{}]", uf.undeclared_features.join(", "));
            if !uf.borrowed_from.is_empty() {
                outln!(sink, "    borrowed from: {}", uf.borrowed_from.join(", "));
            }
            if !uf.required_by.is_empty() {
                outln!(sink, "    required by: {}", uf.required_by.join(", "));
            }
            if let Some(target) = &uf.target {
                outln!(sink, "    target: {}", target);
            }
            outln!(
                sink,
                "    reason: standalone compiler failure names a feature currently supplied by another member"
            );
            outln!(sink);
        }
    }

    // Explain why no changes if plan is empty
    if plan.workspace_deps.is_empty()
        && plan.member_edits.is_empty()
        && plan.transitive_pins.is_empty()
        && plan.unused_deps.is_empty()
    {
        outln!(sink, "No unification opportunities found.");
        outln!(sink);
        outln!(sink, "Possible reasons:");
        outln!(sink, "  - Dependencies are already unified");
        outln!(sink, "  - Dependencies have incompatible versions (see issues above)");
        outln!(sink, "  - Dependencies are excluded via [unify].exclude config");
        outln!(sink, "  - Dependencies are renamed (use include_renamed = true)");
        outln!(sink, "  - Single-use dependencies (not shared across crates)");
    }
}

/// Check if a workspace is a "virtual" workspace (has [workspace] but no [package])
///
/// Virtual workspaces cannot have [dev-dependencies] directly in their manifest,
/// which affects transitive dependency pinning.
fn is_virtual_workspace(ctx: &WorkspaceContext) -> RailResult<bool> {
    let doc = root_manifest_document(ctx)?;
    // A virtual workspace has [workspace] but no [package]
    Ok(doc.contains_key("workspace") && !doc.contains_key("package"))
}

fn workspace_msrv_write_needed(ctx: &WorkspaceContext, msrv: &semver::Version) -> RailResult<bool> {
    let doc = root_manifest_document(ctx)?;
    let desired = format!("{}.{}.{}", msrv.major, msrv.minor, msrv.patch);
    let current = doc
        .get("workspace")
        .and_then(|ws| ws.get("package"))
        .and_then(|pkg| pkg.get("rust-version"))
        .and_then(|v| v.as_str());

    let Some(current) = current else {
        return Ok(true);
    };
    let Some(current_version) = crate::cargo::multi_target_metadata::parse_rust_version(current) else {
        return Ok(current != desired);
    };
    if current_version > *msrv {
        return Ok(false);
    }
    Ok(current != desired)
}

fn transitive_pins_host_manifest_path(ctx: &WorkspaceContext) -> RailResult<std::path::PathBuf> {
    let transitive_host_setting = ctx
        .config()
        .and_then(|config| config.unify.transitive_pinning.as_ref())
        .map(|pinning| &pinning.host);
    let is_root_host = matches!(
        transitive_host_setting,
        None | Some(crate::config::TransitiveFeatureHost::Root)
    );

    // For virtual workspaces (no [package] section), we can't use the root as the transitive host
    // because virtual manifests can't have [dev-dependencies].
    if is_root_host && is_virtual_workspace(ctx)? {
        // Auto-select first workspace member as the host
        let members = ctx.graph().workspace_members();
        if members.is_empty() {
            return Err(RailError::with_help(
        "transitive pinning host `root` is incompatible with virtual workspaces".to_string(),
        "Virtual workspaces cannot have [dev-dependencies]. Set transitive_pinning.host to a workspace member path in your rail.toml:\n  \
           [unify]\n  \
           transitive_pinning = { host = \"crates/some-crate\" }"
          .to_string(),
      ));
        }

        let first_member = &members[0];
        if let Some(pkg) = ctx.cargo().get_package(first_member) {
            let member_path = pkg
                .manifest_path
                .parent()
                .ok_or_else(|| RailError::message(format!("Invalid manifest path: {}", pkg.manifest_path)))?;
            return Ok(member_path.join("Cargo.toml").into_std_path_buf());
        }

        return Err(RailError::message("Failed to find a suitable transitive host member"));
    }

    Ok(match transitive_host_setting {
        Some(crate::config::TransitiveFeatureHost::Path(p)) => ctx.workspace_root().join(p).join("Cargo.toml"),
        _ => ctx.workspace_root().join("Cargo.toml"),
    })
}

fn build_unify_mutation_plan(
    ctx: &WorkspaceContext,
    plan: &crate::cargo::UnificationPlan,
    msrv_write_needed: bool,
    backup_enabled: bool,
    no_report: bool,
    report_path: Option<&std::path::PathBuf>,
) -> RailResult<mutation::MutationPlan> {
    let (actions, risks, trace) =
        build_unify_mutation_parts(ctx, plan, msrv_write_needed, backup_enabled, no_report, report_path)?;
    mutation::build_plan(ctx, "unify", actions, risks, trace)
}

fn unify_expected_mutation(ctx: &WorkspaceContext, path: &Path) -> RailResult<ExpectedMutation> {
    let absolute = if path.is_absolute() {
        path.to_path_buf()
    } else {
        ctx.snapshot()?.cargo_current_dir().join(path)
    };
    let authority_root = if ctx.has_git() {
        &ctx.git()?.git().worktree_root
    } else {
        ctx.workspace_root()
    };
    let relative = crate::utils::path_relative_to(authority_root, &absolute).map_err(|error| {
        RailError::message(format!(
            "unify mutation path '{}' is outside authority root '{}': {error}",
            absolute.display(),
            authority_root.display()
        ))
    })?;
    let relative = PathBuf::from(crate::utils::path_to_git_format(&relative));
    Ok(ExpectedMutation::capture(
        authority_root,
        relative,
        MutationEffect::Write,
    ))
}

fn unify_report_output_path(
    ctx: &WorkspaceContext,
    plan: &crate::cargo::UnificationPlan,
    no_report: bool,
    requested: Option<&Path>,
) -> RailResult<Option<PathBuf>> {
    if no_report {
        return Ok(None);
    }
    let requested = requested
        .map(Path::to_path_buf)
        .unwrap_or_else(|| crate::workspace::cargo_rail_state_root(ctx.workspace_root()).join("unify-report.md"));
    let absolute = if requested.is_absolute() {
        requested
    } else {
        ctx.snapshot()?.cargo_current_dir().join(requested)
    };
    let output = crate::utils::canonicalize_allow_missing(&absolute).map_err(|error| {
        RailError::message(format!("resolving unify report path '{}': {error}", absolute.display()))
    })?;
    let authority_root = if ctx.has_git() {
        &ctx.git()?.git().worktree_root
    } else {
        ctx.workspace_root()
    };
    crate::utils::path_relative_to(authority_root, &output).map_err(|error| {
        RailError::message(format!(
            "unify report path '{}' is outside authority root '{}': {error}",
            output.display(),
            authority_root.display()
        ))
    })?;

    let mut protected = BTreeSet::from([
        ctx.workspace_root().join("Cargo.toml"),
        ctx.workspace_root().join("Cargo.lock"),
    ]);
    protected.extend(plan.member_paths.values().cloned());
    if !plan.transitive_pins.is_empty() {
        protected.insert(transitive_pins_host_manifest_path(ctx)?);
    }
    for path in protected {
        let path = crate::utils::canonicalize_allow_missing(&path).map_err(|error| {
            RailError::message(format!("resolving protected unify path '{}': {error}", path.display()))
        })?;
        if output == path {
            return Err(RailError::with_help(
                format!(
                    "unify report path '{}' aliases a graph mutation target",
                    output.display()
                ),
                "choose a report path that is distinct from every Cargo.toml and Cargo.lock",
            ));
        }
    }
    Ok(Some(output))
}

fn build_unify_mutation_parts(
    ctx: &WorkspaceContext,
    plan: &crate::cargo::UnificationPlan,
    msrv_write_needed: bool,
    backup_enabled: bool,
    no_report: bool,
    report_path: Option<&std::path::PathBuf>,
) -> RailResult<(Vec<MutationAction>, Vec<MutationRisk>, Vec<MutationTrace>)> {
    let mut actions = Vec::with_capacity(8); // Typically few distinct action types
    let mut risks = Vec::with_capacity(4);
    let mut trace = Vec::with_capacity(8);
    let proof_certificates = proof_certificates_to_json(plan, msrv_write_needed);
    let proof_fingerprint = proof_set_fingerprint(&proof_certificates);

    actions.push(
        MutationAction::new(
            "VERIFY_PROOF_SET",
            "portable unify proof certificates",
            Some(proof_fingerprint.clone()),
        )
        .with_payload(serde_json::json!({
          "schema_version": 1,
          "proof_fingerprint": proof_fingerprint,
        })),
    );

    if !plan.workspace_deps.is_empty() {
        actions.push(
            MutationAction::new(
                "WRITE_WORKSPACE_DEPS",
                "Cargo.toml:[workspace.dependencies]",
                Some(format!("{} dependencies", plan.workspace_deps.len())),
            )
            .with_mutations(vec![unify_expected_mutation(
                ctx,
                &ctx.workspace_root().join("Cargo.toml"),
            )?]),
        );
    }

    if !plan.member_edits.is_empty() {
        let mut members = plan
            .member_edits
            .keys()
            .map(|member| {
                let path = plan
                    .member_paths
                    .get(member)
                    .ok_or_else(|| RailError::message(format!("member path not found: {member}")))?;
                unify_expected_mutation(ctx, path)
            })
            .collect::<RailResult<Vec<_>>>()?;
        members.sort_by(|left, right| left.path.cmp(&right.path));
        actions.push(
            MutationAction::new(
                "APPLY_MEMBER_EDITS",
                "workspace member manifests",
                Some(format!("{} member(s)", plan.member_edits.len())),
            )
            .with_mutations(members),
        );
    }

    if !plan.transitive_pins.is_empty() {
        let mut mutations = vec![unify_expected_mutation(ctx, &ctx.workspace_root().join("Cargo.toml"))?];
        let host = unify_expected_mutation(ctx, &transitive_pins_host_manifest_path(ctx)?)?;
        if mutations.iter().all(|mutation| mutation.path != host.path) {
            mutations.push(host);
        }
        actions.push(
            MutationAction::new(
                "APPLY_TRANSITIVE_PINS",
                "transitive host manifest",
                Some(format!("{} pinned dependencies", plan.transitive_pins.len())),
            )
            .with_mutations(mutations),
        );
    }

    if msrv_write_needed {
        actions.push(
            MutationAction::new(
                "WRITE_WORKSPACE_MSRV",
                "Cargo.toml:[workspace.package.rust-version]",
                None,
            )
            .with_mutations(vec![unify_expected_mutation(
                ctx,
                &ctx.workspace_root().join("Cargo.toml"),
            )?]),
        );
    }

    if plan.has_planned_changes(msrv_write_needed) {
        actions.push(
            MutationAction::new(
                "REFRESH_CARGO_LOCK",
                "Cargo.lock",
                Some("Cargo resolves the authorized manifest graph".to_string()),
            )
            .with_mutations(vec![unify_expected_mutation(
                ctx,
                &ctx.workspace_root().join("Cargo.lock"),
            )?]),
        );
    }

    if backup_enabled && plan.has_planned_changes(msrv_write_needed) {
        actions.push(MutationAction::new("CREATE_BACKUP", "target/cargo-rail/backups", None));
    }

    if !no_report && plan.has_planned_changes(msrv_write_needed) {
        let path = unify_report_output_path(ctx, plan, false, report_path.map(PathBuf::as_path))?
            .ok_or_else(|| RailError::message("unify report path unexpectedly disabled"))?;
        let mutation = unify_expected_mutation(ctx, &path)?;
        actions.push(
            MutationAction::new("WRITE_REPORT", mutation.path.display().to_string(), None)
                .with_mutations(vec![mutation]),
        );
    }

    let error_count = plan
        .issues
        .iter()
        .filter(|issue| issue.severity == crate::cargo::IssueSeverity::Error)
        .count();
    if error_count > 0 {
        risks.push(MutationRisk::new(
            "BLOCKING_ISSUES",
            "high",
            format!("{} blocking issue(s) detected", error_count),
        ));
    }

    if !plan.transitive_pins.is_empty() {
        risks.push(MutationRisk::new(
            "TRANSITIVE_PIN_SIDE_EFFECTS",
            "medium",
            "transitive pinning mutates host dev-dependencies",
        ));
    }

    trace.push(MutationTrace::new(
        "UNIFY_ANALYSIS_COMPLETE",
        format!(
            "planned {} workspace dep(s), {} member edit(s), {} transitive pin(s)",
            plan.workspace_deps.len(),
            plan.member_edit_count(),
            plan.transitive_pins.len()
        ),
    ));
    if !plan.workspace_deps.is_empty() {
        trace.push(MutationTrace::new(
            "UNIFY_VERSION_DECISIONS",
            format!(
                "resolved versions for {} workspace dependency entries",
                plan.workspace_deps.len()
            ),
        ));
    }
    let feature_edit_count: usize = plan
        .member_edits
        .values()
        .flat_map(|edits| edits.iter())
        .filter(|edit| {
            matches!(
                edit,
                crate::cargo::MemberEdit::AddFeatures { .. } | crate::cargo::MemberEdit::RemoveFeature { .. }
            )
        })
        .count();
    if feature_edit_count > 0 {
        trace.push(MutationTrace::new(
            "UNIFY_FEATURE_DECISIONS",
            format!("planned {} feature-level member edit(s)", feature_edit_count),
        ));
    }
    let package_inheritance_edit_count = plan.package_inheritance_edit_count();
    if package_inheritance_edit_count > 0 {
        trace.push(MutationTrace::new(
            "UNIFY_PACKAGE_INHERITANCE_DECISIONS",
            format!(
                "planned {} equivalent package declaration(s) for workspace inheritance",
                package_inheritance_edit_count
            ),
        ));
    }
    if msrv_write_needed || plan.computed_msrv.is_some() {
        trace.push(MutationTrace::new(
            "UNIFY_MSRV_DECISIONS",
            format!(
                "msrv evaluated: computed={}, write_needed={}",
                plan.computed_msrv.is_some(),
                msrv_write_needed
            ),
        ));
    }
    if !plan.transitive_pins.is_empty() {
        trace.push(MutationTrace::new(
            "UNIFY_TRANSITIVE_DECISIONS",
            format!("planned {} transitive pin decision(s)", plan.transitive_pins.len()),
        ));
    }

    Ok((actions, risks, trace))
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::cargo::{
        DepKind, UnificationPlan, UnifyDecision, UnifyDecisionCode, UnifyDecisionReason, UnifyDecisionSubject,
    };
    use rustc_hash::FxHashMap;
    use std::sync::Arc;

    fn arc(value: &str) -> Arc<str> {
        Arc::from(value)
    }

    fn empty_plan() -> UnificationPlan {
        UnificationPlan {
            workspace_deps: Vec::new(),
            member_edits: FxHashMap::default(),
            member_paths: FxHashMap::default(),
            transitive_pins: Vec::new(),
            issues: Vec::new(),
            computed_msrv: None,
            duplicates_cleaned: Vec::new(),
            pruned_features: Vec::new(),
            reachable_features: Vec::new(),
            optional_features: Vec::new(),
            version_mismatches: Vec::new(),
            unused_deps: Vec::new(),
            undeclared_features: Vec::new(),
            package_inheritance: Vec::new(),
            dependency_decisions: Vec::new(),
        }
    }

    #[test]
    fn test_dependency_decisions_to_json_includes_reason_codes() {
        let mut plan = empty_plan();
        plan.dependency_decisions.push(UnifyDecision {
            dep_name: arc("tokio"),
            subject: UnifyDecisionSubject::UndeclaredFeatureFix,
            member: Some(arc("crate-b")),
            target: Some(arc("cfg(unix)")),
            reasons: vec![UnifyDecisionReason {
                code: UnifyDecisionCode::UndeclaredFeatureFix,
                summary: arc("Added missing features locally."),
                features: vec![arc("macros")],
                members: vec![arc("crate-b")],
                borrowed_from: vec![arc("crate-a")],
                feature_paths: Vec::new(),
            }],
        });

        let json = dependency_decisions_to_json(&plan);
        assert_eq!(json.len(), 1);
        assert_eq!(json[0]["dep_name"], "tokio");
        assert_eq!(json[0]["subject"], "undeclared_feature_fix");
        assert_eq!(json[0]["member"], "crate-b");
        assert_eq!(json[0]["target"], "cfg(unix)");
        assert_eq!(json[0]["reasons"][0]["code"], "undeclared_feature_fix");
        assert_eq!(json[0]["reasons"][0]["features"][0], "macros");
        assert_eq!(json[0]["reasons"][0]["borrowed_from"][0], "crate-a");
    }

    #[test]
    fn test_relative_path_distinguishes_portable_sibling_path_dependencies() {
        assert_eq!(
            relative_path(Path::new("/checkout/workspace"), Path::new("/checkout/vendor/alpha")),
            Some(PathBuf::from("../vendor/alpha"))
        );
        assert_eq!(
            relative_path(Path::new("/checkout/workspace"), Path::new("/checkout/vendor/beta")),
            Some(PathBuf::from("../vendor/beta"))
        );
    }

    #[test]
    fn test_msrv_toolchain_constraint_distinguishes_identity_from_probe_evidence() {
        let required = semver::Version::new(1, 90, 0);

        assert_eq!(
            msrv_toolchain_constraint(Some(&required), "1.90.0").0,
            MsrvToolchainConstraintStatus::Satisfied
        );
        assert_eq!(
            msrv_toolchain_constraint(Some(&required), "1.91.0-nightly").0,
            MsrvToolchainConstraintStatus::Satisfied
        );
        assert_eq!(
            msrv_toolchain_constraint(Some(&required), "1.89.0").0,
            MsrvToolchainConstraintStatus::Unsatisfied
        );
        assert_eq!(
            msrv_toolchain_constraint(Some(&required), "unknown").0,
            MsrvToolchainConstraintStatus::Unknown
        );
        assert_eq!(
            msrv_toolchain_constraint(None, "1.90.0").0,
            MsrvToolchainConstraintStatus::NotApplicable
        );
    }

    #[test]
    fn test_display_explain_renders_dependency_decisions() {
        let mut plan = empty_plan();
        plan.dependency_decisions.extend([
            UnifyDecision {
                dep_name: arc("serde"),
                subject: UnifyDecisionSubject::WorkspaceDependency,
                member: None,
                target: None,
                reasons: vec![
                    UnifyDecisionReason {
                        code: UnifyDecisionCode::FeatureIntersection,
                        summary: arc("Used intersection to keep only shared features."),
                        features: vec![arc("derive")],
                        members: vec![arc("crate-a"), arc("crate-b")],
                        borrowed_from: Vec::new(),
                        feature_paths: Vec::new(),
                    },
                    UnifyDecisionReason {
                        code: UnifyDecisionCode::ExactPinWarnCaret,
                        summary: arc("Converted exact pin to ^1.0.200."),
                        features: Vec::new(),
                        members: vec![arc("crate-a"), arc("crate-b")],
                        borrowed_from: Vec::new(),
                        feature_paths: Vec::new(),
                    },
                ],
            },
            UnifyDecision {
                dep_name: arc("tokio"),
                subject: UnifyDecisionSubject::WorkspaceDependency,
                member: None,
                target: None,
                reasons: vec![UnifyDecisionReason {
                    code: UnifyDecisionCode::CohortEnforced,
                    summary: arc("Enforced atomic workspace-member cohort."),
                    features: Vec::new(),
                    members: vec![arc("tokio"), arc("tokio-stream"), arc("tokio-util")],
                    borrowed_from: Vec::new(),
                    feature_paths: Vec::new(),
                }],
            },
            UnifyDecision {
                dep_name: arc("windows-sys"),
                subject: UnifyDecisionSubject::TransitivePin,
                member: None,
                target: None,
                reasons: vec![UnifyDecisionReason {
                    code: UnifyDecisionCode::TransitivePin,
                    summary: arc("Pinned transitively to stabilize target-specific feature resolution."),
                    features: vec![arc("Win32_Foundation")],
                    members: Vec::new(),
                    borrowed_from: Vec::new(),
                    feature_paths: Vec::new(),
                }],
            },
            UnifyDecision {
                dep_name: arc("tokio"),
                subject: UnifyDecisionSubject::UndeclaredFeatureFix,
                member: Some(arc("crate-c")),
                target: None,
                reasons: vec![UnifyDecisionReason {
                    code: UnifyDecisionCode::UndeclaredFeatureFix,
                    summary: arc("Added missing features to stop borrowed resolver state."),
                    features: vec![arc("macros")],
                    members: vec![arc("crate-c")],
                    borrowed_from: vec![arc("crate-a")],
                    feature_paths: Vec::new(),
                }],
            },
        ]);
        plan.member_edits.insert(
            arc("crate-c"),
            vec![crate::cargo::MemberEdit::AddFeatures {
                dep_name: arc("tokio"),
                dep_kind: DepKind::Normal,
                target: None,
                features_to_add: vec![arc("macros")],
            }],
        );

        let mut sink = UnifyTextSink::new(true);
        display_explain(&mut sink, &plan);
        let output = sink.finish().expect("captured output");

        assert!(output.contains("Dependency decisions:"));
        assert!(output.contains("intersection: Used intersection to keep only shared features."));
        assert!(output.contains("exact_pin_warn_caret: Converted exact pin to ^1.0.200."));
        assert!(output.contains("cohort_enforced: Enforced atomic workspace-member cohort."));
        assert!(
            output.contains("transitive_pin: Pinned transitively to stabilize target-specific feature resolution.")
        );
        assert!(output.contains("undeclared_feature_fix: Added missing features to stop borrowed resolver state."));
        assert!(output.contains("borrowed from: crate-a"));
    }
}