supercode_harness/

skills_control.rs

//! Controlled-tier skills (Domain 11, concept 15) — `install` and `remove`,
//! each through the door the harness itself publishes.
//!
//! Charter (`docs/plans/orchestration-domain-11-2026-09-02.md` §0.4):
//! supercode never runs a skill registry, never resolves a slug, never
//! unpacks an archive. Every mutation is the harness's own door:
//!
//! * **Hermes** — `hermes skills install <identifier> --yes` /
//!   `hermes skills uninstall <name> --yes`, with `HERMES_HOME` in the
//!   environment. The pinned help (`parity/fixtures/hermes-help.txt`,
//!   re-checked against the installed 0.21.0) says the positional is a
//!   registry identifier or a direct HTTP(S) URL to a `SKILL.md`; hermes
//!   publishes NO local-directory install form, so a local path is refused
//!   rather than handed to a verb that cannot take it.
//! * **OpenClaw** — `openclaw skills install <skill-ref>` (`@owner/slug`,
//!   `git:<repo>`, or a local skill directory; `--global` for the shared
//!   managed directory, `--as <slug>` to name it). At the pin there is NO
//!   `openclaw skills remove`, so `remove` is refused with
//!   `UnsupportedAction` — supercode does not delete files behind the
//!   harness's back.
//! * **Claude Code, Codex, opencode, pi** — the door IS the directory. These
//!   four have no skills CLI at all; a skill is installed by placing its
//!   package at the root the harness's own loader reads
//!   (`crate::skills::writable_skill_roots`, transcribed from the same
//!   inventories ORCH-11 reads), and removed by deleting that directory.
//!   Both operations are confined to those roots: a name that would escape
//!   one, or a package the loader does not recognize, is refused.
//! * **supercode itself** — refused: it has no skills root of its own
//!   (`crate::skills::SKILL_HARNESSES` names the six harnesses it reads).
//!
//! The three ORCH-18 rules are inherited verbatim:
//!
//! 1. **The harness's answer is the answer.** After the door succeeds the row
//!    is re-read through the ORCH-11 loader ([`crate::skills::list_skills`])
//!    and returned; a `remove` that leaves the row behind is a failure. Note
//!    that `hermes skills install` exits 0 on a fetch failure, so the re-read
//!    — not the exit status — is what decides.
//! 2. **The door is narrated.** Every outcome carries `ran`: the harness
//!    command that was executed, or the directory operation in its shell
//!    spelling (`cp -R <source> <dest>`, `rm -r <dest>`).
//! 3. **A door the harness does not have is refused**
//!    ([`SkillControlError::Unsupported`] → `UnsupportedAction`), never a
//!    silent no-op and never a file supercode writes on its own authority.

use std::collections::BTreeSet;
use std::path::{Path, PathBuf};

use serde::{Deserialize, Serialize};

use crate::jobs_control::{harness_program, shell_quote, HarnessCommand, JobControlError};
use crate::skills::{
    declared_skill_name, list_skills, skill_roots, writable_skill_roots, SkillHomes, SkillRow,
    SkillScope, SkillsQuery, SKILL_HARNESSES,
};
use crate::HarnessId;

/// Harnesses whose installed skills supercode can MUTATE through a door the
/// harness publishes. Identical to [`SKILL_HARNESSES`] today: the two CLI
/// harnesses have a verb, the core four have their loader's directory.
pub const CONTROLLED_SKILL_HARNESSES: &[&str] = SKILL_HARNESSES;

/// Why supercode refuses to install a skill into itself.
pub const SUPERCODE_REFUSAL: &str =
    "supercode has no skills root of its own: its skill surface is the SIX harnesses it reads \
     (`skills.list`), so there is nothing here to install into. Name the harness whose root the \
     package belongs in";

/// Why `remove` is refused on OpenClaw at the pinned version.
pub const OPENCLAW_REMOVE_REFUSAL: &str =
    "openclaw 2026.7.1-2 publishes no `skills remove` verb (`openclaw skills` has \
     search|install|update|verify|curator|workshop|list|info|check). supercode refuses rather \
     than deleting files out of the harness's managed directory behind its back";

/// One uniform mutating verb.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum SkillVerb {
    /// Place a skill package where the harness's loader reads it.
    Install,
    /// Take a skill package back out.
    Remove,
}

impl SkillVerb {
    /// Uniform spelling used in the RPC method and in outcomes.
    pub const fn as_str(self) -> &'static str {
        match self {
            Self::Install => "install",
            Self::Remove => "remove",
        }
    }
}

/// One mutating request, in the uniform Domain 11 vocabulary.
#[derive(Debug, Clone, Default, PartialEq, Eq, Serialize, Deserialize)]
#[serde(default)]
pub struct SkillMutation {
    /// Harness whose root the package belongs in.
    pub harness: String,
    /// Skill name. Required by `remove`; on `install` it overrides the name
    /// the package declares (`hermes --name`, `openclaw --as`, the directory
    /// name for the core four).
    pub name: Option<String>,
    /// What to install: a local skill directory, or — where the harness's own
    /// verb accepts one — its registry identifier / URL.
    pub source: Option<String>,
    /// Which root class to act in. `user` (the default) or `project`.
    pub scope: Option<SkillScope>,
    /// Working tree whose project roots are addressed. Defaults to the
    /// process working directory, exactly as `skills.list` does.
    pub cwd: Option<PathBuf>,
    /// Config homes, so an isolated home is addressed the same way the read
    /// side addresses it.
    pub homes: SkillHomes,
}

/// What one mutation did, with the harness's own row read back afterwards.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct SkillMutationOutcome {
    /// Harness that owns the root.
    pub harness: String,
    /// Uniform verb that was asked for.
    pub verb: String,
    /// The harness command, or the directory operation, that was performed.
    pub ran: String,
    /// Affected skill name.
    pub name: String,
    /// The skill as the ORCH-11 loader reports it AFTER the verb. Absent for
    /// `remove`.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub skill: Option<SkillRow>,
    /// `true` on a successful `remove`.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub removed: Option<bool>,
}

/// Why a mutation could not be performed.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum SkillControlError {
    /// The harness has no door for what was asked (refused, never faked).
    Unsupported(String),
    /// The request itself is incoherent.
    Invalid(String),
    /// The door was opened and failed; the message carries what it said.
    Failed(String),
}

impl std::fmt::Display for SkillControlError {
    fn fmt(&self, formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::Unsupported(message) | Self::Invalid(message) | Self::Failed(message) => {
                formatter.write_str(message)
            }
        }
    }
}

impl std::error::Error for SkillControlError {}

impl From<JobControlError> for SkillControlError {
    fn from(error: JobControlError) -> Self {
        match error {
            JobControlError::Unsupported(message) => Self::Unsupported(message),
            JobControlError::Invalid(message) => Self::Invalid(message),
            JobControlError::Failed(message) => Self::Failed(message),
        }
    }
}

type Result<T> = std::result::Result<T, SkillControlError>;

/// Whether `harness` has any skills door supercode can drive.
pub fn supports_skill_control(harness: &str) -> bool {
    CONTROLLED_SKILL_HARNESSES.contains(&harness)
}

fn unsupported_harness(harness: &str) -> String {
    if harness == HarnessId::SUPERCODE {
        return SUPERCODE_REFUSAL.to_string();
    }
    format!(
        "`{harness}` has no skills root Volter Harness reads; skills verbs are supported for: {}",
        CONTROLLED_SKILL_HARNESSES.join(", ")
    )
}

/// Perform one mutation through the harness's own door, then re-read the row.
pub fn mutate_skill(verb: SkillVerb, mutation: &SkillMutation) -> Result<SkillMutationOutcome> {
    if !supports_skill_control(&mutation.harness) {
        return Err(SkillControlError::Unsupported(unsupported_harness(
            &mutation.harness,
        )));
    }
    let scope = mutation.scope.unwrap_or(SkillScope::User);
    if !matches!(scope, SkillScope::User | SkillScope::Project) {
        return Err(SkillControlError::Invalid(format!(
            "`{}` is a root the harness owns, not one a client may write; use user or project",
            scope.as_str()
        )));
    }
    match mutation.harness.as_str() {
        HarnessId::HERMES => hermes(verb, mutation, scope),
        HarnessId::OPENCLAW => openclaw(verb, mutation, scope),
        _ => directory(verb, mutation, scope),
    }
}

// ---------------------------------------------------------------------------
// Shared: re-reading through the ORCH-11 loader
// ---------------------------------------------------------------------------

fn cwd_of(mutation: &SkillMutation) -> PathBuf {
    mutation
        .cwd
        .clone()
        .or_else(|| std::env::current_dir().ok())
        .unwrap_or_else(|| PathBuf::from("."))
}

/// Every skill the harness's own loader reports right now.
fn read_rows(mutation: &SkillMutation) -> Vec<SkillRow> {
    list_skills(&SkillsQuery {
        harness: Some(mutation.harness.clone()),
        scope: None,
        cwd: Some(cwd_of(mutation)),
        homes: mutation.homes.clone(),
    })
}

fn read_names(mutation: &SkillMutation) -> BTreeSet<String> {
    read_rows(mutation)
        .into_iter()
        .map(|row| row.name)
        .collect()
}

fn find_by_name(mutation: &SkillMutation, name: &str) -> Option<SkillRow> {
    read_rows(mutation).into_iter().find(|row| row.name == name)
}

fn find_at(mutation: &SkillMutation, location: &Path) -> Option<SkillRow> {
    read_rows(mutation)
        .into_iter()
        .find(|row| row.location == location)
}

fn require_source(mutation: &SkillMutation) -> Result<&str> {
    mutation
        .source
        .as_deref()
        .map(str::trim)
        .filter(|value| !value.is_empty())
        .ok_or_else(|| {
            SkillControlError::Invalid(
                "`skills.install` needs a `source`: a local skill directory, or the identifier \
                 the harness's own install verb accepts"
                    .into(),
            )
        })
}

fn require_name(mutation: &SkillMutation) -> Result<&str> {
    mutation
        .name
        .as_deref()
        .map(str::trim)
        .filter(|value| !value.is_empty())
        .ok_or_else(|| {
            SkillControlError::Invalid("`skills.remove` needs the skill `name` to remove".into())
        })
}

/// A skill name that can only ever address one directory INSIDE a root.
///
/// This is the containment gate for the directory door: the name comes from a
/// package's own frontmatter, so `../…`, an absolute path, or a separator in
/// it would otherwise write outside the root the harness reads.
fn validate_name(name: &str) -> Result<&str> {
    let trimmed = name.trim();
    let rejected = trimmed.is_empty()
        || trimmed == "."
        || trimmed == ".."
        || trimmed.starts_with('.')
        || trimmed.contains('/')
        || trimmed.contains('\\')
        || trimmed.contains('\0')
        || Path::new(trimmed).components().count() != 1;
    if rejected {
        return Err(SkillControlError::Invalid(format!(
            "`{name}` is not a skill name: a skill is one directory inside the harness's own \
             root, so a name may not be empty, hidden, or contain a path separator"
        )));
    }
    Ok(trimmed)
}

// ---------------------------------------------------------------------------
// Hermes — `hermes skills install | uninstall` over HERMES_HOME
// ---------------------------------------------------------------------------

/// Hermes's own argv for one verb, ready to run and ready to narrate.
fn hermes_command(
    verb: SkillVerb,
    mutation: &SkillMutation,
    scope: SkillScope,
) -> Result<HarnessCommand> {
    if scope != SkillScope::User {
        return Err(SkillControlError::Unsupported(
            "hermes keeps skills in one root per HERMES_HOME (`<HERMES_HOME>/skills`, and a \
             profile IS a HERMES_HOME); it has no project-scoped skills root, so supercode \
             refuses rather than inventing one"
                .into(),
        ));
    }
    let mut command = HarnessCommand::new(harness_program(HarnessId::HERMES)?);
    command.env("HERMES_HOME", mutation.homes.hermes.to_string_lossy());
    command.arg("skills");
    match verb {
        SkillVerb::Install => {
            let source = require_source(mutation)?;
            if Path::new(source).is_dir() {
                return Err(SkillControlError::Unsupported(format!(
                    "`hermes skills install` takes a registry identifier (`owner/repo/skills/x`) \
                     or a direct HTTP(S) URL to a SKILL.md — its pinned help enumerates no \
                     local-directory form, so `{source}` cannot be handed to it. Serve the \
                     package's SKILL.md over HTTP, or install it into a harness whose door is the \
                     directory"
                )));
            }
            command.args(["install", "--yes"]);
            if let Some(name) = trimmed_name(mutation) {
                command.args(["--name", name]);
            }
            command.arg(source);
        }
        SkillVerb::Remove => {
            command.args(["uninstall", require_name(mutation)?, "--yes"]);
        }
    }
    Ok(command)
}

fn hermes(
    verb: SkillVerb,
    mutation: &SkillMutation,
    scope: SkillScope,
) -> Result<SkillMutationOutcome> {
    let command = hermes_command(verb, mutation, scope)?;
    run_and_reread(verb, mutation, command)
}

/// Run one CLI door, then let the ORCH-11 loader answer for what it did.
///
/// `hermes skills install` prints a failed fetch and still exits 0, so the
/// harness's own root — never the exit status alone — decides.
fn run_and_reread(
    verb: SkillVerb,
    mutation: &SkillMutation,
    command: HarnessCommand,
) -> Result<SkillMutationOutcome> {
    let ran = command.narrate();
    match verb {
        SkillVerb::Install => {
            let before = read_names(mutation);
            command.run().map_err(SkillControlError::Failed)?;
            let name = installed_name(mutation, &before, trimmed_name(mutation), &ran)?;
            let skill = find_by_name(mutation, &name).ok_or_else(|| {
                SkillControlError::Failed(format!(
                    "`{ran}` exited 0 but {}'s skills roots hold no `{name}` afterwards",
                    mutation.harness
                ))
            })?;
            Ok(SkillMutationOutcome {
                harness: mutation.harness.clone(),
                verb: verb.as_str().to_string(),
                ran,
                name,
                skill: Some(skill),
                removed: None,
            })
        }
        SkillVerb::Remove => {
            let name = require_name(mutation)?.to_string();
            command.run().map_err(SkillControlError::Failed)?;
            refuse_if_still_present(mutation, &name, &ran)?;
            Ok(SkillMutationOutcome {
                harness: mutation.harness.clone(),
                verb: verb.as_str().to_string(),
                ran,
                name,
                skill: None,
                removed: Some(true),
            })
        }
    }
}

fn trimmed_name(mutation: &SkillMutation) -> Option<&str> {
    mutation
        .name
        .as_deref()
        .map(str::trim)
        .filter(|name| !name.is_empty())
}

/// Which skill a CLI install verb actually landed: the name the harness's own
/// root GAINED. A caller-supplied name decides between several.
fn installed_name(
    mutation: &SkillMutation,
    before: &BTreeSet<String>,
    requested: Option<&str>,
    ran: &str,
) -> Result<String> {
    let after = read_names(mutation);
    let mut fresh: Vec<String> = after.difference(before).cloned().collect();
    if fresh.len() == 1 {
        return Ok(fresh.remove(0));
    }
    if let Some(name) = requested {
        if after.contains(name) {
            return Ok(name.to_string());
        }
    }
    Err(SkillControlError::Failed(format!(
        "`{ran}` exited 0 but {}'s skills root gained {} skill(s), so the installed skill cannot \
         be identified — pass `name` to say which one it should be",
        mutation.harness,
        fresh.len()
    )))
}

fn refuse_if_still_present(mutation: &SkillMutation, name: &str, ran: &str) -> Result<()> {
    match find_by_name(mutation, name) {
        Some(row) => Err(SkillControlError::Failed(format!(
            "`{ran}` reported success but `{name}` is still installed at {}",
            row.location.display()
        ))),
        None => Ok(()),
    }
}

// ---------------------------------------------------------------------------
// OpenClaw — `openclaw skills install`; no remove verb at the pin
// ---------------------------------------------------------------------------

/// OpenClaw's own argv. `remove` never reaches the runner: the pin has no verb.
fn openclaw_command(
    verb: SkillVerb,
    mutation: &SkillMutation,
    scope: SkillScope,
) -> Result<HarnessCommand> {
    if matches!(verb, SkillVerb::Remove) {
        return Err(SkillControlError::Unsupported(
            OPENCLAW_REMOVE_REFUSAL.to_string(),
        ));
    }
    let source = require_source(mutation)?;
    let mut command = HarnessCommand::new(harness_program(HarnessId::OPENCLAW)?);
    // The same environment contract the read side and `jobs_control` use:
    // `OPENCLAW_STATE_DIR` names the state dir, `OPENCLAW_CONFIG_PATH` the
    // config file inside it, so an isolated home stays isolated.
    command.env(
        "OPENCLAW_STATE_DIR",
        mutation.homes.openclaw.to_string_lossy(),
    );
    command.env(
        "OPENCLAW_CONFIG_PATH",
        mutation
            .homes
            .openclaw
            .join("openclaw.json")
            .to_string_lossy(),
    );
    command.args(["skills", "install", source]);
    // OpenClaw's own two destinations: the shared managed directory, or the
    // agent workspace. `user` is the shared one; `project` is the workspace
    // the CLI infers, which is also where the ORCH-11 loader reads it from.
    if scope == SkillScope::User {
        command.arg("--global");
    }
    if let Some(name) = trimmed_name(mutation) {
        command.args(["--as", name]);
    }
    Ok(command)
}

fn openclaw(
    verb: SkillVerb,
    mutation: &SkillMutation,
    scope: SkillScope,
) -> Result<SkillMutationOutcome> {
    let command = openclaw_command(verb, mutation, scope)?;
    run_and_reread(verb, mutation, command)
}

// ---------------------------------------------------------------------------
// Claude Code, Codex, opencode, pi — the door IS the directory
// ---------------------------------------------------------------------------

fn directory(
    verb: SkillVerb,
    mutation: &SkillMutation,
    scope: SkillScope,
) -> Result<SkillMutationOutcome> {
    let cwd = cwd_of(mutation);
    let roots = writable_skill_roots(&mutation.harness, scope, &mutation.homes, &cwd);
    if roots.is_empty() {
        return Err(SkillControlError::Unsupported(format!(
            "`{}` has no {} skills root Volter Harness may write; its inventory names none",
            mutation.harness,
            scope.as_str()
        )));
    }
    match verb {
        SkillVerb::Install => directory_install(mutation, scope, &roots),
        SkillVerb::Remove => directory_remove(mutation, scope, &roots, &cwd),
    }
}

fn directory_install(
    mutation: &SkillMutation,
    scope: SkillScope,
    roots: &[PathBuf],
) -> Result<SkillMutationOutcome> {
    let source = PathBuf::from(require_source(mutation)?);
    if !source.is_dir() {
        return Err(SkillControlError::Invalid(format!(
            "`{}` is not a directory: `{}`'s skills door is its loader's own root, so the source \
             must be the skill PACKAGE — a directory holding SKILL.md",
            source.display(),
            mutation.harness
        )));
    }
    let declared = declared_skill_name(&source).ok_or_else(|| {
        SkillControlError::Invalid(format!(
            "`{}` holds no SKILL.md, so it is not a skill package the harness's loader would \
             read",
            source.display()
        ))
    })?;
    let requested = mutation
        .name
        .as_deref()
        .map(str::trim)
        .filter(|name| !name.is_empty())
        .unwrap_or(declared.as_str());
    let name = validate_name(requested)?.to_string();
    let root = &roots[0];
    let destination = root.join(&name);
    if destination.exists() {
        return Err(SkillControlError::Invalid(format!(
            "`{name}` is already installed at {}; remove it first",
            destination.display()
        )));
    }
    std::fs::create_dir_all(root).map_err(|error| {
        SkillControlError::Failed(format!(
            "{}'s {} skills root {} could not be created: {error}",
            mutation.harness,
            scope.as_str(),
            root.display()
        ))
    })?;
    contained_in(&destination, std::slice::from_ref(root))?;
    let ran = format!(
        "cp -R {} {}",
        shell_quote(&source.to_string_lossy()),
        shell_quote(&destination.to_string_lossy())
    );
    if let Err(error) = copy_package(&source, &destination) {
        // Never leave half a package where the loader would read it.
        let _ = std::fs::remove_dir_all(&destination);
        return Err(error);
    }
    let skill = find_at(mutation, &destination).ok_or_else(|| {
        SkillControlError::Failed(format!(
            "`{ran}` succeeded but {}'s loader does not report a skill at {}",
            mutation.harness,
            destination.display()
        ))
    })?;
    Ok(SkillMutationOutcome {
        harness: mutation.harness.clone(),
        verb: SkillVerb::Install.as_str().to_string(),
        ran,
        name: skill.name.clone(),
        skill: Some(skill),
        removed: None,
    })
}

fn directory_remove(
    mutation: &SkillMutation,
    scope: SkillScope,
    writable: &[PathBuf],
    cwd: &Path,
) -> Result<SkillMutationOutcome> {
    let name = validate_name(require_name(mutation)?)?.to_string();
    let matches: Vec<SkillRow> = read_rows(mutation)
        .into_iter()
        .filter(|row| row.name == name && row.scope == scope)
        .collect();
    let row = match matches.len() {
        0 => {
            return Err(SkillControlError::Invalid(format!(
                "`{}` has no {} skill `{name}`",
                mutation.harness,
                scope.as_str()
            )))
        }
        1 => matches.into_iter().next().expect("one match"),
        _ => {
            return Err(SkillControlError::Invalid(format!(
                "`{}` reports {} skills named `{name}` in its {} roots ({}); supercode refuses to \
                 guess which one to delete",
                mutation.harness,
                matches.len(),
                scope.as_str(),
                matches
                    .iter()
                    .map(|row| row.location.display().to_string())
                    .collect::<Vec<_>>()
                    .join(", ")
            )))
        }
    };
    // Containment: the package must sit directly under a root this harness's
    // own loader consults, writable or already-existing.
    let mut recognized: Vec<PathBuf> = writable.to_vec();
    recognized.extend(
        skill_roots(&mutation.harness, &mutation.homes, cwd)
            .into_iter()
            .filter(|(found, _)| *found == scope)
            .map(|(_, root)| root),
    );
    contained_in(&row.location, &recognized)?;
    if !row.location.join("SKILL.md").is_file() {
        return Err(SkillControlError::Invalid(format!(
            "{} holds no SKILL.md; supercode removes skill PACKAGES, never a directory it cannot \
             identify as one",
            row.location.display()
        )));
    }
    let ran = format!("rm -r {}", shell_quote(&row.location.to_string_lossy()));
    std::fs::remove_dir_all(&row.location)
        .map_err(|error| SkillControlError::Failed(format!("`{ran}` failed: {error}")))?;
    refuse_if_still_present(mutation, &name, &ran)?;
    Ok(SkillMutationOutcome {
        harness: mutation.harness.clone(),
        verb: SkillVerb::Remove.as_str().to_string(),
        ran,
        name,
        skill: None,
        removed: Some(true),
    })
}

/// Refuse any path that is not a DIRECT child of one of `roots`.
///
/// Both sides are canonicalized as far as they exist, so a symlinked home
/// (`/tmp` → `/private/tmp` on macOS) and a `..` inside the path are compared
/// the same way the filesystem would resolve them.
fn contained_in(path: &Path, roots: &[PathBuf]) -> Result<()> {
    let resolved = resolve(path);
    for root in roots {
        let root = resolve(root);
        if resolved.parent() == Some(root.as_path()) {
            return Ok(());
        }
    }
    Err(SkillControlError::Invalid(format!(
        "{} is outside the skills roots supercode recognizes ({}); every install and removal \
         stays inside the harness's own root",
        path.display(),
        roots
            .iter()
            .map(|root| root.display().to_string())
            .collect::<Vec<_>>()
            .join(", ")
    )))
}

/// Canonicalize the longest existing prefix and re-attach the rest, so a
/// destination that does not exist yet still compares against a real root.
fn resolve(path: &Path) -> PathBuf {
    if let Ok(canonical) = path.canonicalize() {
        return canonical;
    }
    match (path.parent(), path.file_name()) {
        (Some(parent), Some(name)) => resolve(parent).join(name),
        _ => path.to_path_buf(),
    }
}

/// Copy a skill package. Regular files and directories only: a symlink could
/// point anywhere, so it is refused rather than followed or silently dropped.
fn copy_package(source: &Path, destination: &Path) -> Result<()> {
    std::fs::create_dir_all(destination).map_err(|error| {
        SkillControlError::Failed(format!(
            "{} could not be created: {error}",
            destination.display()
        ))
    })?;
    let entries = std::fs::read_dir(source).map_err(|error| {
        SkillControlError::Failed(format!("{} could not be read: {error}", source.display()))
    })?;
    for entry in entries {
        let entry = entry.map_err(|error| {
            SkillControlError::Failed(format!("{} could not be read: {error}", source.display()))
        })?;
        let from = entry.path();
        let kind = std::fs::symlink_metadata(&from).map_err(|error| {
            SkillControlError::Failed(format!("{} could not be read: {error}", from.display()))
        })?;
        let to = destination.join(entry.file_name());
        if kind.is_symlink() {
            return Err(SkillControlError::Invalid(format!(
                "{} is a symlink; supercode copies a skill package's own files only, so a link \
                 that could point outside it is refused",
                from.display()
            )));
        }
        if kind.is_dir() {
            copy_package(&from, &to)?;
        } else if kind.is_file() {
            std::fs::copy(&from, &to).map_err(|error| {
                SkillControlError::Failed(format!(
                    "{} could not be copied to {}: {error}",
                    from.display(),
                    to.display()
                ))
            })?;
        } else {
            return Err(SkillControlError::Invalid(format!(
                "{} is neither a file nor a directory; a skill package holds only its own files",
                from.display()
            )));
        }
    }
    Ok(())
}