perspt-sdk 0.6.6

//! Capability-constrained admissibility kernel (PSP-8 System 7).
//!
//! Stochastic components emit proposals, never unmediated effects. Every effect
//! passes through an admissibility kernel before execution. This module is the
//! domain-neutral reference kernel and contract; `perspt-policy` is the
//! deterministic trusted base that adopts it. Generated code, prompts, domain
//! packages, and subagents are outside that trusted base.
//!
//! Authority is an explicit, attenuable value: delegation may only *shrink*
//! effect scope, call budget, expiry, and delegability (the attenuation
//! preorder `c' ⪯ c`). Payload data, model text, or generated code cannot mint
//! authority (PSP-8 R4).

use ed25519_dalek::{Signature, Signer, SigningKey, Verifier, VerifyingKey};
use serde::{Deserialize, Serialize};

use crate::command::{classify_tier, CommandInvocation, CommandTier};
use crate::error::SdkError;

/// An actor that can hold capabilities and emit proposals.
#[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize, Deserialize)]
pub struct ActorId(pub String);

impl ActorId {
    pub fn new(id: impl Into<String>) -> Self {
        Self(id.into())
    }
}

/// Effect classes (PSP-8 System 7).
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum EffectKind {
    ReadFile,
    /// Read-only operating-system and toolchain facts.
    SystemProbe,
    /// Read-only, bounded queries over explicitly selected data sources.
    DataRead,
    ToolSearch,
    ToolProgram,
    Search,
    List,
    LspQuery,
    WriteArtifact,
    ApplyPatch,
    MoveFile,
    DeleteFile,
    RunVerifier,
    RunFormatter,
    RunTest,
    RunBuild,
    MutateDependencies,
    RunRepoScript,
    RunShell,
    GitRead,
    GitWrite,
    NetworkFetch,
    AskUser,
    SpawnAgent,
    UpdateGraph,
    UpdatePolicy,
}

impl EffectKind {
    /// Read-only effects allowed in workspace scope by default.
    pub fn is_read_only(self) -> bool {
        matches!(
            self,
            EffectKind::ReadFile
                | EffectKind::SystemProbe
                | EffectKind::DataRead
                | EffectKind::ToolSearch
                | EffectKind::ToolProgram
                | EffectKind::Search
                | EffectKind::List
                | EffectKind::LspQuery
                | EffectKind::GitRead
        )
    }

    /// Privileged effects that self-modifying agents must never grant themselves.
    pub fn is_privileged(self) -> bool {
        matches!(self, EffectKind::UpdateGraph | EffectKind::UpdatePolicy)
    }
}

/// Risk classification for a proposed effect.
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum RiskClass {
    None,
    Low,
    Medium,
    High,
    Critical,
}

pub use crate::scope::{CommandPattern, NetworkPattern, PathPattern};

/// A recorded risk budget (PSP-8 System 7).
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct RiskBudget {
    pub name: String,
    /// Total budget `ρ_c`.
    pub limit: f64,
    /// Amount already spent `spent(x)`.
    pub spent: f64,
}

impl RiskBudget {
    pub fn new(name: impl Into<String>, limit: f64) -> Self {
        Self {
            name: name.into(),
            limit,
            spent: 0.0,
        }
    }

    /// Whether `spent + cost <= limit`.
    pub fn admits(&self, cost: f64) -> bool {
        self.spent + cost <= self.limit
    }
}

/// Approval policy for an effect.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum ApprovalPolicy {
    /// Allowed without explicit approval (within scope).
    Auto,
    /// Requires user approval.
    Ask,
    /// Allowed because an approved session policy covers it.
    SessionApproved,
    /// Never allowed.
    Deny,
}

/// Role-scoped authority template. Role is part of attenuation and cannot be
/// changed by proposal payload data.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum CapabilityRole {
    Session,
    /// Interactive chat external tools. Kept distinct from coding workers so
    /// chat eligibility cannot widen agent authority.
    ChatTool,
    Explorer,
    Worker,
    Reviewer,
}

/// Durable authorization intent. A resume re-mints a fresh live capability
/// from this policy and current workspace facts; the capability itself is
/// deliberately not serializable.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct GrantPolicy {
    pub policy_id: String,
    pub workspace_root: String,
    pub effect_ceiling: Vec<EffectKind>,
    pub path_ceiling: Vec<PathPattern>,
    pub command_ceiling: Vec<CommandPattern>,
    pub network_ceiling: Vec<NetworkPattern>,
    pub approval_ceiling: ApprovalPolicy,
    pub authority_epoch: u64,
    pub persistent: bool,
    /// Content binding recorded in the session ledger. Persistent policies
    /// require a separate cryptographic signature before cross-session use.
    pub integrity_binding: String,
}

/// Scope intersection for `GrantPolicy::mint`. An empty ceiling means
/// unbounded for allow-when-empty scopes (paths, commands) and *no authority*
/// for deny-when-empty scopes (network). A `*` on either side defers to the
/// other side's bound.
fn intersect_scope(
    requested: Vec<String>,
    ceiling: &[String],
    deny_when_empty_ceiling: bool,
) -> Vec<String> {
    if ceiling.is_empty() {
        return if deny_when_empty_ceiling {
            Vec::new()
        } else {
            requested
        };
    }
    if ceiling.iter().any(|pattern| pattern == "*") {
        return requested;
    }
    if requested.is_empty() || requested.iter().any(|pattern| pattern == "*") {
        return ceiling.to_vec();
    }
    requested
        .into_iter()
        .filter(|pattern| ceiling.iter().any(|allowed| allowed == pattern))
        .collect()
}

impl GrantPolicy {
    /// Mint a live capability as the intersection of a requested template
    /// with this policy's ceilings (PSP-9 resolved decision 6). Fails closed:
    /// an empty effect intersection is an error, never an unlimited grant.
    ///
    /// The approval ceiling governs durable delivery. A `Worker`-role request
    /// confined to the reversible candidate overlay may keep `Auto` inside an
    /// `Ask` ceiling, because nothing it does becomes durable without the
    /// separate promotion approval; every other role is clamped to the
    /// stricter policy.
    pub fn mint(&self, mut requested: Capability) -> crate::error::Result<Capability> {
        requested
            .effects
            .retain(|effect| self.effect_ceiling.contains(effect));
        if requested.effects.is_empty() {
            return Err(SdkError::Domain(
                "grant intersection authorizes no effects".into(),
            ));
        }
        let unwrap_paths = |patterns: Vec<PathPattern>| -> Vec<String> {
            patterns.into_iter().map(|p| p.0).collect()
        };
        requested.path_scope = intersect_scope(
            unwrap_paths(requested.path_scope),
            &self
                .path_ceiling
                .iter()
                .map(|p| p.0.clone())
                .collect::<Vec<_>>(),
            false,
        )
        .into_iter()
        .map(PathPattern)
        .collect();
        requested.command_scope = intersect_scope(
            requested.command_scope.into_iter().map(|p| p.0).collect(),
            &self
                .command_ceiling
                .iter()
                .map(|p| p.0.clone())
                .collect::<Vec<_>>(),
            false,
        )
        .into_iter()
        .map(CommandPattern)
        .collect();
        requested.network_scope = intersect_scope(
            requested.network_scope.into_iter().map(|p| p.0).collect(),
            &self
                .network_ceiling
                .iter()
                .map(|p| p.0.clone())
                .collect::<Vec<_>>(),
            true,
        )
        .into_iter()
        .map(NetworkPattern)
        .collect();
        if requested.role != CapabilityRole::Worker
            && requested.approval_policy.strictness() < self.approval_ceiling.strictness()
        {
            requested.approval_policy = self.approval_ceiling;
        }
        requested.authority_epoch = self.authority_epoch;
        Ok(requested)
    }

    /// The deterministic byte encoding the grant signature commits to.
    ///
    /// serde output is not canonical (field order, float and escape formatting
    /// may change across versions), so the signature covers this fixed,
    /// length-prefixed encoding instead. Every field participates; list fields
    /// are count-prefixed so no concatenation can alias two policies.
    pub fn canonical_bytes(&self) -> Vec<u8> {
        fn field(out: &mut Vec<u8>, bytes: &[u8]) {
            out.extend_from_slice(&(bytes.len() as u64).to_be_bytes());
            out.extend_from_slice(bytes);
        }
        fn list(out: &mut Vec<u8>, entries: impl ExactSizeIterator<Item = String>) {
            out.extend_from_slice(&(entries.len() as u64).to_be_bytes());
            for entry in entries {
                field(out, entry.as_bytes());
            }
        }
        let mut out = Vec::new();
        field(&mut out, b"perspt-grant-policy-v1");
        field(&mut out, self.policy_id.as_bytes());
        field(&mut out, self.workspace_root.as_bytes());
        list(
            &mut out,
            self.effect_ceiling.iter().map(|e| format!("{e:?}")),
        );
        list(&mut out, self.path_ceiling.iter().map(|p| p.0.clone()));
        list(&mut out, self.command_ceiling.iter().map(|p| p.0.clone()));
        list(&mut out, self.network_ceiling.iter().map(|p| p.0.clone()));
        field(&mut out, format!("{:?}", self.approval_ceiling).as_bytes());
        out.extend_from_slice(&self.authority_epoch.to_be_bytes());
        out.push(u8::from(self.persistent));
        field(&mut out, self.integrity_binding.as_bytes());
        out
    }
}

/// Signed durable grant intent. Verification authenticates policy bytes only;
/// resume must still intersect the policy with the current authority epoch,
/// workspace facts, and configured ceilings before minting a new capability.
///
/// The embedded public key is *not* a trust anchor — anyone can re-sign a
/// rewritten policy with their own key. Callers MUST verify against the key
/// they trust via [`SignedGrantPolicy::verify_against`].
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct SignedGrantPolicy {
    pub policy: GrantPolicy,
    pub public_key: String,
    pub signature: String,
}

impl SignedGrantPolicy {
    pub fn sign(policy: GrantPolicy, secret_key: &[u8; 32]) -> crate::error::Result<Self> {
        let signing_key = SigningKey::from_bytes(secret_key);
        let signature = signing_key.sign(&policy.canonical_bytes());
        Ok(Self {
            policy,
            public_key: hex_encode(signing_key.verifying_key().as_bytes()),
            signature: hex_encode(&signature.to_bytes()),
        })
    }

    /// Verify the signature against a caller-supplied trusted public key.
    ///
    /// This is the only verification that authenticates the policy: it fails
    /// both on a bad signature and on a signer other than `trusted_public_key`.
    pub fn verify_against(&self, trusted_public_key: &[u8; 32]) -> crate::error::Result<()> {
        let embedded: [u8; 32] = hex_decode(&self.public_key)?
            .try_into()
            .map_err(|_| SdkError::Signature("grant public key must be 32 bytes".into()))?;
        if &embedded != trusted_public_key {
            return Err(SdkError::Signature(
                "grant signed by an untrusted key".into(),
            ));
        }
        let signature: [u8; 64] = hex_decode(&self.signature)?
            .try_into()
            .map_err(|_| SdkError::Signature("grant signature must be 64 bytes".into()))?;
        let verifying_key = VerifyingKey::from_bytes(&embedded)
            .map_err(|error| SdkError::Signature(error.to_string()))?;
        verifying_key
            .verify(
                &self.policy.canonical_bytes(),
                &Signature::from_bytes(&signature),
            )
            .map_err(|error| SdkError::Signature(error.to_string()))
    }
}

/// Derive the Ed25519 public key for a grant signing key, so callers can
/// anchor [`SignedGrantPolicy::verify_against`] to the key they resolved
/// without taking their own dependency on the signature crate.
pub fn grant_public_key(secret_key: &[u8; 32]) -> [u8; 32] {
    SigningKey::from_bytes(secret_key)
        .verifying_key()
        .to_bytes()
}

/// Lowercase hex encoding, shared by grant signing and key persistence.
pub fn hex_encode(bytes: &[u8]) -> String {
    use std::fmt::Write;
    let mut output = String::with_capacity(bytes.len() * 2);
    for byte in bytes {
        let _ = write!(&mut output, "{byte:02x}");
    }
    output
}

/// Inverse of [`hex_encode`].
pub fn hex_decode(value: &str) -> crate::error::Result<Vec<u8>> {
    if value.len() & 1 != 0 {
        return Err(SdkError::Signature("hex value has odd length".into()));
    }
    (0..value.len())
        .step_by(2)
        .map(|index| {
            u8::from_str_radix(&value[index..index + 2], 16)
                .map_err(|error| SdkError::Signature(format!("invalid hex value: {error}")))
        })
        .collect()
}

impl ApprovalPolicy {
    /// Ordering for the attenuation preorder: a child's policy must be at
    /// least as strict as its parent's (PSP-9 system 12).
    pub fn strictness(self) -> u8 {
        match self {
            ApprovalPolicy::Auto | ApprovalPolicy::SessionApproved => 0,
            ApprovalPolicy::Ask => 1,
            ApprovalPolicy::Deny => 2,
        }
    }
}

/// A capability: an explicit, attenuable grant of authority (PSP-8 System 7).
#[derive(Debug, Clone, PartialEq)]
pub struct Capability {
    pub capability_id: String,
    pub holder: ActorId,
    pub effects: Vec<EffectKind>,
    pub path_scope: Vec<PathPattern>,
    /// Mutation-only path ceiling (PSP-10 system 22): the node's declared
    /// `output_targets`. Reads stay governed by `path_scope` alone; empty
    /// means unrestricted (undeclared targets).
    pub write_scope: Vec<PathPattern>,
    pub command_scope: Vec<CommandPattern>,
    pub network_scope: Vec<NetworkPattern>,
    /// Remaining call budget `q_c`. `None` means unbounded.
    pub max_calls: Option<u32>,
    /// Expiry `τ_c` as a unix timestamp. `None` means no expiry.
    pub expires_at: Option<i64>,
    /// Delegability `d_c`.
    pub may_delegate: bool,
    pub risk_budget: Option<RiskBudget>,
    pub approval_policy: ApprovalPolicy,
    pub session_id: String,
    pub authority_epoch: u64,
    pub graph_revision: String,
    pub node_generation: u32,
    pub role: CapabilityRole,
    pub parent_capability_id: Option<String>,
}

impl Capability {
    pub fn new(holder: ActorId, effects: Vec<EffectKind>) -> Self {
        Self {
            capability_id: uuid::Uuid::new_v4().to_string(),
            holder,
            effects,
            path_scope: Vec::new(),
            write_scope: Vec::new(),
            command_scope: Vec::new(),
            network_scope: Vec::new(),
            max_calls: None,
            expires_at: None,
            may_delegate: false,
            risk_budget: None,
            approval_policy: ApprovalPolicy::Auto,
            session_id: String::new(),
            authority_epoch: 0,
            graph_revision: String::new(),
            node_generation: 0,
            role: CapabilityRole::Session,
            parent_capability_id: None,
        }
    }

    pub fn with_paths(mut self, patterns: Vec<&str>) -> Self {
        self.path_scope = patterns
            .into_iter()
            .map(|p| PathPattern(p.to_string()))
            .collect();
        self
    }

    pub fn delegable(mut self) -> Self {
        self.may_delegate = true;
        self
    }

    pub fn grants(&self, effect: EffectKind) -> bool {
        self.effects.contains(&effect)
    }

    /// The attenuation preorder `c' ⪯ c`: a delegated capability may only shrink
    /// effect scope, call budget, expiry, and delegability (PSP-8 System 7).
    pub fn attenuates(&self, source: &Capability) -> bool {
        // Effects subset.
        if !self.effects.iter().all(|e| source.effects.contains(e)) {
            return false;
        }
        // Path/command/network scope subset (each pattern must be covered).
        // All three scopes are part of Perspt's effective `E_c` and MUST
        // participate in the Def. 4.1 preorder (PSP-9 system 12, Gate L).
        // Empty child scope means unbounded only when the parent is also
        // unbounded; it must never widen a bounded parent.
        fn scope_attenuates<T: PartialEq>(
            child: &[T],
            parent: &[T],
            parent_has_wildcard: bool,
        ) -> bool {
            if parent.is_empty() {
                return true; // unbounded parent admits any child scope
            }
            if child.is_empty() {
                return false; // bounded parent, unbounded child: widening
            }
            child
                .iter()
                .all(|c| parent_has_wildcard || parent.contains(c))
        }
        let path_wild = source.path_scope.iter().any(|sp| sp.0 == "*");
        if !scope_attenuates(&self.path_scope, &source.path_scope, path_wild) {
            return false;
        }
        let write_wild = source.write_scope.iter().any(|sp| sp.0 == "*");
        if !scope_attenuates(&self.write_scope, &source.write_scope, write_wild) {
            return false;
        }
        let cmd_wild = source.command_scope.iter().any(|sp| sp.0 == "*");
        if !scope_attenuates(&self.command_scope, &source.command_scope, cmd_wild) {
            return false;
        }
        // Network scope is deny-by-default at admissibility time (an empty
        // scope grants no network authority), so its preorder must invert:
        // an empty parent scope bounds the child to empty, and a non-empty
        // child must be covered by the parent. Reusing the allow-by-default
        // rule here would let a no-network parent delegate `*` (widening).
        if source.network_scope.is_empty() {
            if !self.network_scope.is_empty() {
                return false;
            }
        } else {
            let net_wild = source.network_scope.iter().any(|sp| sp.0 == "*");
            if !self
                .network_scope
                .iter()
                .all(|c| net_wild || source.network_scope.contains(c))
            {
                return false;
            }
        }
        // Call budget no greater.
        if let (Some(child), Some(parent)) = (self.max_calls, source.max_calls) {
            if child > parent {
                return false;
            }
        }
        if self.max_calls.is_none() && source.max_calls.is_some() {
            return false; // child unbounded but parent bounded
        }
        // Expiry no later.
        if let (Some(child), Some(parent)) = (self.expires_at, source.expires_at) {
            if child > parent {
                return false;
            }
        }
        if self.expires_at.is_none() && source.expires_at.is_some() {
            return false;
        }
        // Delegability no greater.
        if self.may_delegate && !source.may_delegate {
            return false;
        }
        // Risk budget no larger (PSP-9): a bounded parent bounds the child.
        match (&self.risk_budget, &source.risk_budget) {
            (Some(child), Some(parent))
                if child.limit - child.spent > parent.limit - parent.spent =>
            {
                return false;
            }
            (None, Some(_)) => return false, // child unbounded, parent bounded
            _ => {}
        }
        // Approval policy at least as strict.
        if self.approval_policy.strictness() < source.approval_policy.strictness() {
            return false;
        }
        if self.session_id != source.session_id
            || self.authority_epoch != source.authority_epoch
            || self.graph_revision != source.graph_revision
            || self.node_generation != source.node_generation
        {
            return false;
        }
        if self.role == CapabilityRole::Session && source.role != CapabilityRole::Session {
            return false;
        }
        if self.parent_capability_id.as_deref() != Some(source.capability_id.as_str()) {
            return false;
        }
        true
    }

    /// Attempt to delegate an attenuated child capability. Returns `None` if the
    /// source is not delegable or the child does not satisfy the preorder.
    pub fn delegate(&self, child: Capability) -> Option<Capability> {
        if !self.may_delegate {
            return None;
        }
        // The child holder may differ (the delegatee); attenuation governs scope.
        if child.attenuates(self) {
            Some(child)
        } else {
            None
        }
    }
}

/// A state witness: a content hash of a precondition that must still hold at
/// execution time (PSP-8 System 7).
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct StateWitness {
    pub resource: String,
    pub content_hash: String,
}

/// An effect proposal (PSP-8 System 7).
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct EffectProposal {
    pub proposal_id: String,
    pub actor: ActorId,
    pub node_id: String,
    pub generation: u32,
    pub effect: EffectKind,
    /// The path the effect touches, if any.
    pub path: Option<String>,
    /// Additional paths touched by a multi-path effect such as a move.
    #[serde(default)]
    pub additional_paths: Vec<String>,
    /// The command, if this is an execution effect.
    pub command: Option<CommandInvocation>,
    /// The network target, if any.
    pub network_target: Option<String>,
    pub risk: RiskClass,
    /// Cost charged against the capability risk budget `c_c`.
    pub risk_cost: f64,
    pub idempotency_key: String,
    pub preconditions: Vec<StateWitness>,
}

impl EffectProposal {
    pub fn new(actor: ActorId, node_id: impl Into<String>, effect: EffectKind) -> Self {
        Self {
            proposal_id: uuid::Uuid::new_v4().to_string(),
            actor,
            node_id: node_id.into(),
            generation: 0,
            effect,
            path: None,
            additional_paths: Vec::new(),
            command: None,
            network_target: None,
            risk: RiskClass::Low,
            risk_cost: 0.0,
            idempotency_key: uuid::Uuid::new_v4().to_string(),
            preconditions: Vec::new(),
        }
    }

    pub fn with_path(mut self, path: impl Into<String>) -> Self {
        self.path = Some(path.into());
        self
    }

    pub fn with_additional_paths(mut self, paths: Vec<String>) -> Self {
        self.additional_paths = paths;
        self
    }

    pub fn with_command(mut self, command: CommandInvocation) -> Self {
        self.command = Some(command);
        self
    }

    // --- PSP-9 system 12 builders. The certified increment `c_c` and the
    // budget debit come from the registered capability contract and
    // `BarrierWitness`, never from model arguments, so there is no
    // `with_risk_cost` builder. ---

    pub fn with_generation(mut self, generation: u32) -> Self {
        self.generation = generation;
        self
    }

    pub fn with_risk_class(mut self, risk: RiskClass) -> Self {
        self.risk = risk;
        self
    }

    pub fn with_network_target(mut self, target: impl Into<String>) -> Self {
        self.network_target = Some(target.into());
        self
    }

    pub fn with_idempotency_key(mut self, key: impl Into<String>) -> Self {
        self.idempotency_key = key.into();
        self
    }

    pub fn with_preconditions(mut self, preconditions: Vec<StateWitness>) -> Self {
        self.preconditions = preconditions;
        self
    }
}

/// The admissibility decision.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(tag = "decision", rename_all = "snake_case")]
pub enum AdmissibilityDecision {
    Allow,
    Deny { reason: DenyReason },
    NeedsApproval,
}

/// Why an effect was denied.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum DenyReason {
    NoCapability,
    EffectOutOfScope,
    PathOutOfScope,
    CommandOutOfScope,
    NetworkOutOfScope,
    CallBudgetExhausted,
    Expired,
    RiskBudgetExhausted,
    StateWitnessMismatch,
    ShellNotPermitted,
    MutationNotPermitted,
    PolicyDenied,
    PrivilegeEscalation,
}

/// Recovery classification for a denied or failed effect.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum RecoveryClass {
    Retryable,
    NeedsApproval,
    NeedsCapability,
    Fatal,
}

/// The witness produced by checking a proposal (PSP-8 `AdmissibilityWitness`).
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct AdmissibilityWitness {
    pub proposal_id: String,
    pub actor: ActorId,
    pub capability_id: Option<String>,
    pub authority_ok: bool,
    pub contract_ok: bool,
    pub effect_ok: bool,
    pub barrier_increment_ok: bool,
    pub risk_budget_ok: bool,
    pub decision: AdmissibilityDecision,
    pub recovery_class: Option<RecoveryClass>,
}

/// The current durable state the kernel reads when checking a proposal.
#[derive(Debug, Clone, Default)]
pub struct KernelState {
    /// Live content hashes of resources, for state-witness validation.
    pub witnesses: std::collections::HashMap<String, String>,
}

impl KernelState {
    pub fn new() -> Self {
        Self::default()
    }

    pub fn set_witness(&mut self, resource: impl Into<String>, hash: impl Into<String>) {
        self.witnesses.insert(resource.into(), hash.into());
    }
}

fn deny(
    proposal: &EffectProposal,
    cap: Option<&Capability>,
    reason: DenyReason,
    recovery: RecoveryClass,
) -> AdmissibilityWitness {
    AdmissibilityWitness {
        proposal_id: proposal.proposal_id.clone(),
        actor: proposal.actor.clone(),
        capability_id: cap.map(|c| c.capability_id.clone()),
        authority_ok: cap.is_some(),
        contract_ok: false,
        effect_ok: false,
        barrier_increment_ok: false,
        risk_budget_ok: false,
        decision: AdmissibilityDecision::Deny { reason },
        recovery_class: Some(recovery),
    }
}

/// Evaluate the admissibility predicate `Adm(x, p, x')` for a proposal against
/// the actor's capabilities and current kernel state.
///
/// Returns an [`AdmissibilityWitness`] recording each clause and the decision.
/// Every effect SHALL be mediated by such a witness before any durable effect
/// occurs (PSP-8 Gate E).
pub fn check_admissibility(
    proposal: &EffectProposal,
    capabilities: &[Capability],
    state: &KernelState,
) -> AdmissibilityWitness {
    let cap = match find_authorized_capability(proposal, capabilities) {
        Ok(cap) => cap,
        Err(witness) => return *witness,
    };
    if let Some(denied) = check_binding(proposal, cap, state) {
        return denied;
    }
    if let Some(denied) = check_lifetime(proposal, cap, state) {
        return denied;
    }
    if let Some(denied) = check_scope(proposal, cap) {
        return denied;
    }
    if let Some(denied) = check_state_witnesses(proposal, cap, state) {
        return denied;
    }
    finalize_decision(proposal, cap)
}

/// Authority clause: a capability held by the proposing actor that grants the
/// effect. Privileged effects additionally require root, user-minted authority:
/// a delegated or non-session capability cannot carry them, so a self-modifying
/// agent can never launder `UpdateGraph`/`UpdatePolicy` through a child grant.
fn find_authorized_capability<'a>(
    proposal: &EffectProposal,
    capabilities: &'a [Capability],
) -> Result<&'a Capability, Box<AdmissibilityWitness>> {
    let cap = capabilities
        .iter()
        .find(|c| c.holder == proposal.actor && c.grants(proposal.effect))
        .ok_or_else(|| {
            Box::new(deny(
                proposal,
                None,
                DenyReason::NoCapability,
                RecoveryClass::NeedsCapability,
            ))
        })?;
    if proposal.effect.is_privileged()
        && (cap.role != CapabilityRole::Session || cap.parent_capability_id.is_some())
    {
        return Err(Box::new(deny(
            proposal,
            Some(cap),
            DenyReason::PrivilegeEscalation,
            RecoveryClass::Fatal,
        )));
    }
    Ok(cap)
}

/// Binding clause: the capability is bound to the live graph revision,
/// authority epoch, and node generation it was minted for.
fn check_binding(
    proposal: &EffectProposal,
    cap: &Capability,
    state: &KernelState,
) -> Option<AdmissibilityWitness> {
    if !cap.graph_revision.is_empty()
        && state.witnesses.get("__graph_revision") != Some(&cap.graph_revision)
    {
        return Some(deny(
            proposal,
            Some(cap),
            DenyReason::StateWitnessMismatch,
            RecoveryClass::NeedsCapability,
        ));
    }
    if !cap.session_id.is_empty()
        && state
            .witnesses
            .get("__authority_epoch")
            .and_then(|value| value.parse::<u64>().ok())
            != Some(cap.authority_epoch)
    {
        return Some(deny(
            proposal,
            Some(cap),
            DenyReason::StateWitnessMismatch,
            RecoveryClass::NeedsCapability,
        ));
    }
    if proposal.generation != cap.node_generation {
        return Some(deny(
            proposal,
            Some(cap),
            DenyReason::StateWitnessMismatch,
            RecoveryClass::Retryable,
        ));
    }
    None
}

/// Lifetime clause: expiry `τ_c` and call budget `q_c`. An expiry with no
/// `__now` witness fails closed — the kernel cannot certify "not expired"
/// without a clock it trusts, and defaulting to open would make `expires_at`
/// decorative on any path that forgets to supply time.
fn check_lifetime(
    proposal: &EffectProposal,
    cap: &Capability,
    state: &KernelState,
) -> Option<AdmissibilityWitness> {
    if let Some(expiry) = cap.expires_at {
        match state
            .witnesses
            .get("__now")
            .and_then(|s| s.parse::<i64>().ok())
        {
            Some(now) if now <= expiry => {}
            _ => {
                return Some(deny(
                    proposal,
                    Some(cap),
                    DenyReason::Expired,
                    RecoveryClass::NeedsCapability,
                ));
            }
        }
    }
    if cap.max_calls == Some(0) {
        return Some(deny(
            proposal,
            Some(cap),
            DenyReason::CallBudgetExhausted,
            RecoveryClass::NeedsCapability,
        ));
    }
    None
}

/// Scope clause: path, write (mutating proposals only), command, and
/// network scope of the effective `E_c`.
fn check_scope(proposal: &EffectProposal, cap: &Capability) -> Option<AdmissibilityWitness> {
    let mutating_proposal = matches!(
        proposal.effect,
        EffectKind::WriteArtifact
            | EffectKind::ApplyPatch
            | EffectKind::MoveFile
            | EffectKind::DeleteFile
            | EffectKind::MutateDependencies
    );
    for path in proposal.path.iter().chain(proposal.additional_paths.iter()) {
        let out_of_path =
            !cap.path_scope.is_empty() && !cap.path_scope.iter().any(|p| p.matches(path));
        let out_of_write = mutating_proposal
            && !cap.write_scope.is_empty()
            && !cap.write_scope.iter().any(|p| p.matches(path));
        if out_of_path || out_of_write {
            return Some(deny(
                proposal,
                Some(cap),
                DenyReason::PathOutOfScope,
                RecoveryClass::NeedsApproval,
            ));
        }
    }
    if let Some(command) = &proposal.command {
        if command.requires_shell() && !cap.grants(EffectKind::RunShell) {
            return Some(deny(
                proposal,
                Some(cap),
                DenyReason::ShellNotPermitted,
                RecoveryClass::NeedsApproval,
            ));
        }
        if classify_tier(command) == CommandTier::Mutation
            && !mutating_proposal
            && proposal.effect.is_read_only()
        {
            return Some(deny(
                proposal,
                Some(cap),
                DenyReason::MutationNotPermitted,
                RecoveryClass::NeedsApproval,
            ));
        }
        if !cap.command_scope.is_empty()
            && !cap
                .command_scope
                .iter()
                .any(|p| p.matches(command.program_name()))
        {
            return Some(deny(
                proposal,
                Some(cap),
                DenyReason::CommandOutOfScope,
                RecoveryClass::NeedsApproval,
            ));
        }
    }
    if let Some(target) = &proposal.network_target {
        if !cap.network_scope.iter().any(|p| p.matches(target)) {
            return Some(deny(
                proposal,
                Some(cap),
                DenyReason::NetworkOutOfScope,
                RecoveryClass::NeedsApproval,
            ));
        }
    }
    None
}

/// State-witness clause: every recorded precondition hash still holds.
fn check_state_witnesses(
    proposal: &EffectProposal,
    cap: &Capability,
    state: &KernelState,
) -> Option<AdmissibilityWitness> {
    for w in &proposal.preconditions {
        match state.witnesses.get(&w.resource) {
            Some(current) if current == &w.content_hash => {}
            _ => {
                return Some(deny(
                    proposal,
                    Some(cap),
                    DenyReason::StateWitnessMismatch,
                    RecoveryClass::Retryable,
                ));
            }
        }
    }
    None
}

/// Risk-budget and approval clauses, then the final witness.
fn finalize_decision(proposal: &EffectProposal, cap: &Capability) -> AdmissibilityWitness {
    let risk_ok = cap
        .risk_budget
        .as_ref()
        .map(|b| b.admits(proposal.risk_cost))
        .unwrap_or(true);
    if !risk_ok {
        return deny(
            proposal,
            Some(cap),
            DenyReason::RiskBudgetExhausted,
            RecoveryClass::NeedsApproval,
        );
    }
    let decision = match cap.approval_policy {
        ApprovalPolicy::Deny => {
            return deny(
                proposal,
                Some(cap),
                DenyReason::PolicyDenied,
                RecoveryClass::Fatal,
            )
        }
        ApprovalPolicy::Ask => AdmissibilityDecision::NeedsApproval,
        ApprovalPolicy::Auto | ApprovalPolicy::SessionApproved => AdmissibilityDecision::Allow,
    };
    let recovery = match decision {
        AdmissibilityDecision::NeedsApproval => Some(RecoveryClass::NeedsApproval),
        _ => None,
    };
    AdmissibilityWitness {
        proposal_id: proposal.proposal_id.clone(),
        actor: proposal.actor.clone(),
        capability_id: Some(cap.capability_id.clone()),
        authority_ok: true,
        contract_ok: true,
        effect_ok: true,
        barrier_increment_ok: true,
        risk_budget_ok: risk_ok,
        decision,
        recovery_class: recovery,
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::command::canonicalize;

    fn actor() -> ActorId {
        ActorId::new("implementer")
    }

    #[test]
    fn read_only_actor_cannot_write() {
        let caps = vec![Capability::new(
            actor(),
            vec![EffectKind::ReadFile, EffectKind::Search],
        )];
        let proposal =
            EffectProposal::new(actor(), "n1", EffectKind::WriteArtifact).with_path("src/x.rs");
        let w = check_admissibility(&proposal, &caps, &KernelState::new());
        assert!(matches!(
            w.decision,
            AdmissibilityDecision::Deny {
                reason: DenyReason::NoCapability
            }
        ));
    }

    #[test]
    fn write_in_scope_is_allowed() {
        let caps = vec![
            Capability::new(actor(), vec![EffectKind::WriteArtifact]).with_paths(vec!["src/*"])
        ];
        let proposal =
            EffectProposal::new(actor(), "n1", EffectKind::WriteArtifact).with_path("src/x.rs");
        let w = check_admissibility(&proposal, &caps, &KernelState::new());
        assert_eq!(w.decision, AdmissibilityDecision::Allow);
    }

    #[test]
    fn write_out_of_path_scope_is_denied() {
        let caps = vec![
            Capability::new(actor(), vec![EffectKind::WriteArtifact]).with_paths(vec!["src/*"])
        ];
        let proposal =
            EffectProposal::new(actor(), "n1", EffectKind::WriteArtifact).with_path("/etc/passwd");
        let w = check_admissibility(&proposal, &caps, &KernelState::new());
        assert!(matches!(
            w.decision,
            AdmissibilityDecision::Deny {
                reason: DenyReason::PathOutOfScope
            }
        ));
    }

    #[test]
    fn shell_command_denied_without_shell_capability() {
        let mut cap = Capability::new(actor(), vec![EffectKind::RunVerifier]);
        cap.command_scope = vec![CommandPattern("*".into())];
        let proposal = EffectProposal::new(actor(), "n1", EffectKind::RunVerifier)
            .with_command(canonicalize("cat x | grep y", "/r"));
        let w = check_admissibility(&proposal, &[cap], &KernelState::new());
        assert!(matches!(
            w.decision,
            AdmissibilityDecision::Deny {
                reason: DenyReason::ShellNotPermitted
            }
        ));
    }

    #[test]
    fn sed_in_place_denied_under_read_only_effect() {
        let mut cap = Capability::new(actor(), vec![EffectKind::ReadFile]);
        cap.command_scope = vec![CommandPattern("*".into())];
        let proposal = EffectProposal::new(actor(), "n1", EffectKind::ReadFile)
            .with_command(canonicalize("sed -i s/a/b/ f", "/r"));
        let w = check_admissibility(&proposal, &[cap], &KernelState::new());
        assert!(matches!(
            w.decision,
            AdmissibilityDecision::Deny {
                reason: DenyReason::MutationNotPermitted
            }
        ));
    }

    #[test]
    fn stale_state_witness_is_denied() {
        let caps =
            vec![Capability::new(actor(), vec![EffectKind::ApplyPatch]).with_paths(vec!["*"])];
        let mut proposal =
            EffectProposal::new(actor(), "n1", EffectKind::ApplyPatch).with_path("src/x.rs");
        proposal.preconditions = vec![StateWitness {
            resource: "src/x.rs".into(),
            content_hash: "old".into(),
        }];
        let mut state = KernelState::new();
        state.set_witness("src/x.rs", "new"); // changed since proposal
        let w = check_admissibility(&proposal, &caps, &state);
        assert!(matches!(
            w.decision,
            AdmissibilityDecision::Deny {
                reason: DenyReason::StateWitnessMismatch
            }
        ));
    }

    #[test]
    fn risk_budget_exhaustion_is_denied() {
        let mut cap = Capability::new(actor(), vec![EffectKind::ApplyPatch]).with_paths(vec!["*"]);
        cap.risk_budget = Some(RiskBudget {
            name: "session".into(),
            limit: 1.0,
            spent: 0.8,
        });
        let mut proposal =
            EffectProposal::new(actor(), "n1", EffectKind::ApplyPatch).with_path("x");
        proposal.risk_cost = 0.5;
        let w = check_admissibility(&proposal, &[cap], &KernelState::new());
        assert!(matches!(
            w.decision,
            AdmissibilityDecision::Deny {
                reason: DenyReason::RiskBudgetExhausted
            }
        ));
    }

    #[test]
    fn ask_policy_needs_approval() {
        let mut cap = Capability::new(actor(), vec![EffectKind::RunShell]).with_paths(vec!["*"]);
        cap.approval_policy = ApprovalPolicy::Ask;
        cap.command_scope = vec![CommandPattern("*".into())];
        let proposal = EffectProposal::new(actor(), "n1", EffectKind::RunShell)
            .with_command(canonicalize("echo hi | tee x", "/r"));
        let w = check_admissibility(&proposal, &[cap], &KernelState::new());
        assert_eq!(w.decision, AdmissibilityDecision::NeedsApproval);
    }

    #[test]
    fn attenuation_only_shrinks_authority() {
        let parent = Capability::new(
            actor(),
            vec![EffectKind::ReadFile, EffectKind::WriteArtifact],
        )
        .with_paths(vec!["*"])
        .delegable();
        // Valid child: fewer effects, bounded calls.
        let mut child = Capability::new(ActorId::new("sub"), vec![EffectKind::ReadFile])
            .with_paths(vec!["src/*"]);
        child.max_calls = Some(3);
        child.parent_capability_id = Some(parent.capability_id.clone());
        assert!(child.attenuates(&parent));
        assert!(parent.delegate(child).is_some());

        // Invalid child: tries to add an effect the parent lacks.
        let mut bad = Capability::new(ActorId::new("sub"), vec![EffectKind::UpdatePolicy]);
        bad.parent_capability_id = Some(parent.capability_id.clone());
        assert!(!bad.attenuates(&parent));
        assert!(parent.delegate(bad).is_none());
    }

    #[test]
    fn non_delegable_capability_cannot_delegate() {
        let parent = Capability::new(actor(), vec![EffectKind::ReadFile]); // may_delegate = false
        let child = Capability::new(ActorId::new("sub"), vec![EffectKind::ReadFile]);
        assert!(parent.delegate(child).is_none());
    }

    #[test]
    fn payload_cannot_mint_authority() {
        // An actor with no capability at all cannot perform any effect, no matter
        // what the proposal claims.
        let proposal = EffectProposal::new(ActorId::new("ghost"), "n1", EffectKind::UpdatePolicy);
        let w = check_admissibility(&proposal, &[], &KernelState::new());
        assert!(matches!(
            w.decision,
            AdmissibilityDecision::Deny {
                reason: DenyReason::NoCapability
            }
        ));
    }

    #[test]
    fn persistent_grant_signature_detects_policy_tampering() {
        let policy = GrantPolicy {
            policy_id: "p1".into(),
            workspace_root: "/workspace".into(),
            effect_ceiling: vec![EffectKind::ReadFile],
            path_ceiling: vec![PathPattern("src/*".into())],
            command_ceiling: vec![],
            network_ceiling: vec![],
            approval_ceiling: ApprovalPolicy::Ask,
            authority_epoch: 3,
            persistent: true,
            integrity_binding: "ledger:abc".into(),
        };
        let mut signed = SignedGrantPolicy::sign(policy, &[7u8; 32]).unwrap();
        let trusted: [u8; 32] = hex_decode(&signed.public_key).unwrap().try_into().unwrap();
        signed.verify_against(&trusted).unwrap();
        signed.policy.authority_epoch += 1;
        assert!(signed.verify_against(&trusted).is_err());
    }

    #[test]
    fn grant_signature_rejects_an_untrusted_signer() {
        // Re-signing a rewritten policy with a different key must not verify:
        // the embedded public key is not a trust anchor.
        let policy = GrantPolicy {
            policy_id: "p1".into(),
            workspace_root: "/workspace".into(),
            effect_ceiling: vec![EffectKind::ReadFile],
            path_ceiling: vec![],
            command_ceiling: vec![],
            network_ceiling: vec![],
            approval_ceiling: ApprovalPolicy::Ask,
            authority_epoch: 0,
            persistent: true,
            integrity_binding: "ledger:abc".into(),
        };
        let trusted = SignedGrantPolicy::sign(policy.clone(), &[7u8; 32]).unwrap();
        let trusted_key: [u8; 32] = hex_decode(&trusted.public_key).unwrap().try_into().unwrap();
        let mut widened = policy;
        widened.effect_ceiling.push(EffectKind::RunShell);
        let attacker = SignedGrantPolicy::sign(widened, &[9u8; 32]).unwrap();
        assert!(attacker.verify_against(&trusted_key).is_err());
    }

    #[test]
    fn no_network_parent_cannot_delegate_network_authority() {
        let parent = Capability::new(actor(), vec![EffectKind::NetworkFetch]).delegable();
        let mut child = Capability::new(ActorId::new("child"), vec![EffectKind::NetworkFetch]);
        child.parent_capability_id = Some(parent.capability_id.clone());
        child.role = CapabilityRole::Worker;
        child.network_scope = vec![NetworkPattern("*".into())];
        assert!(parent.delegate(child).is_none());
    }

    #[test]
    fn privileged_effect_requires_root_session_authority() {
        // A delegated (child) capability carrying a privileged effect is
        // rejected even though it nominally grants it.
        let mut cap = Capability::new(actor(), vec![EffectKind::UpdatePolicy]);
        cap.role = CapabilityRole::Worker;
        cap.parent_capability_id = Some("parent".into());
        let proposal = EffectProposal::new(actor(), "n1", EffectKind::UpdatePolicy);
        let w = check_admissibility(&proposal, &[cap], &KernelState::new());
        assert!(matches!(
            w.decision,
            AdmissibilityDecision::Deny {
                reason: DenyReason::PrivilegeEscalation
            }
        ));
    }

    #[test]
    fn mint_intersects_the_grant_ceiling_and_fails_closed() {
        let policy = GrantPolicy {
            policy_id: "p1".into(),
            workspace_root: "/workspace".into(),
            effect_ceiling: vec![EffectKind::ReadFile, EffectKind::WriteArtifact],
            path_ceiling: vec![PathPattern("src/*".into())],
            command_ceiling: vec![CommandPattern("rg".into())],
            network_ceiling: vec![],
            approval_ceiling: ApprovalPolicy::Ask,
            authority_epoch: 3,
            persistent: false,
            integrity_binding: "ledger:abc".into(),
        };
        // A widening request is clamped in every dimension.
        let mut requested = Capability::new(
            ActorId::new("worker"),
            vec![EffectKind::ReadFile, EffectKind::RunShell],
        );
        requested.role = CapabilityRole::Worker;
        requested.path_scope = vec![PathPattern("*".into())];
        requested.network_scope = vec![NetworkPattern("*".into())];
        let minted = policy.mint(requested).unwrap();
        assert_eq!(minted.effects, vec![EffectKind::ReadFile]);
        assert_eq!(minted.path_scope, vec![PathPattern("src/*".into())]);
        assert!(minted.network_scope.is_empty(), "no-network ceiling holds");
        assert_eq!(minted.authority_epoch, 3);
        // Worker role keeps Auto inside an Ask ceiling (candidate-only
        // authority); a session role is clamped to the stricter policy.
        assert_eq!(minted.approval_policy, ApprovalPolicy::Auto);
        let mut session = Capability::new(ActorId::new("session"), vec![EffectKind::ReadFile]);
        session.role = CapabilityRole::Session;
        assert_eq!(
            policy.mint(session).unwrap().approval_policy,
            ApprovalPolicy::Ask
        );
        // An empty effect intersection is an error, not an unlimited grant.
        let ghost = Capability::new(ActorId::new("worker"), vec![EffectKind::RunShell]);
        assert!(policy.mint(ghost).is_err());
    }

    #[test]
    fn expiry_without_a_now_witness_fails_closed() {
        let mut cap = Capability::new(actor(), vec![EffectKind::ReadFile]);
        cap.expires_at = Some(1_700_000_000);
        let proposal = EffectProposal::new(actor(), "n1", EffectKind::ReadFile);
        let w = check_admissibility(&proposal, std::slice::from_ref(&cap), &KernelState::new());
        assert!(matches!(
            w.decision,
            AdmissibilityDecision::Deny {
                reason: DenyReason::Expired
            }
        ));
        let mut state = KernelState::new();
        state.set_witness("__now", "1699999999");
        let w = check_admissibility(&proposal, &[cap], &state);
        assert_eq!(w.decision, AdmissibilityDecision::Allow);
    }
}