feat(skill-awareness): T1→T5 — manifeste de skills + outil MCP idea_skill_read

Surface les skills assignés à un agent « à la MCP » : description sur l'entité
Skill (+ effective_description fallback), section « # Skills disponibles » haute
altitude dans le convention-file (mode MCP), outil read-only idea_skill_read
(résolution projet→global), use case ReadSkill (port SkillStore existant), et
câblage au composition root. Dump legacy du corps complet conservé en mode
sans-MCP (zéro régression). Rétro-compat index.json (serde default).

Tests : domain+application+infrastructure 1212 passed / 0 failed (23 ajoutés).
Reste : T6 (champ description front) + T7 (e2e après rebuild AppImage).

NB topologie : commit réalisé par l'orchestrateur car l'agent Git était
injoignable (bug de livraison cold-start) ; à faire relire/rebaser par Git.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/app-tauri/src/commands.rs

@@ -2118,6 +2118,10 @@ pub async fn create_skill(
         .create_skill
         .execute(CreateSkillInput {
             name: request.name,
+            // Description is set via the dedicated frontend field (T6); the create
+            // path stays None for now so the affordance falls back to the body's
+            // first line (see `Skill::effective_description`).
+            description: None,
             content: request.content,
             scope: request.scope,
             project_root: project.root,

crates/app-tauri/src/state.rs

@@ -25,9 +25,9 @@ use application::{
     ListResumableAgents, ListSkills, ListTemplates, LiveAgentRegistry, LiveSessions, LoadLayout,
     McpRuntime, MoveTabToNewWindow, MutateLayout, OnnxModelView, OpenProject, OpenTerminal,
     OrchestratorService, PermissionProjectorRegistry, ProposeContext, ReadAgentContext,
-    ReadContext, ReadMemory, ReadMemoryIndex, ReadProjectContext, RecallMemory, ReconcileLayouts,
-    RecordTurn, RecordTurnProvider, ReferenceProfiles, RenameLayout, ResizeTerminal,
-    ResolveAgentPermissions, ResolveMemoryLinks, SaveEmbedderProfile, SaveProfile,
+    ReadContext, ReadMemory, ReadMemoryIndex, ReadProjectContext, ReadSkill, RecallMemory,
+    ReconcileLayouts, RecordTurn, RecordTurnProvider, ReferenceProfiles, RenameLayout,
+    ResizeTerminal, ResolveAgentPermissions, ResolveMemoryLinks, SaveEmbedderProfile, SaveProfile,
     SessionLimitService, SetActiveLayout, SnapshotRunningAgents, StopLiveAgent, StructuredSessions,
     SuggestedThisSession, SyncAgentWithTemplate, TerminalSessions, UnassignSkillFromAgent,
     UpdateAgentContext, UpdateAgentPermissions, UpdateMemory, UpdateProjectContext,
@@ -965,6 +965,10 @@ impl AppState {
         let update_skill = Arc::new(UpdateSkill::new(Arc::clone(&skill_store_port)));
         let list_skills = Arc::new(ListSkills::new(Arc::clone(&skill_store_port)));
         let delete_skill = Arc::new(DeleteSkill::new(Arc::clone(&skill_store_port)));
+        // Lecture d'un skill par nom pour l'outil MCP `idea_skill_read` (feature
+        // « skills à la MCP ») — compose le SkillStore existant, câblé plus bas sur
+        // l'OrchestratorService via le builder additif `.with_read_skill(...)`.
+        let read_skill = Arc::new(ReadSkill::new(Arc::clone(&skill_store_port)));
         let assign_skill = Arc::new(AssignSkillToAgent::new(
             Arc::clone(&contexts_port),
             Arc::clone(&events_port),
@@ -1189,7 +1193,10 @@ impl AppState {
             .with_memory_harvest(Arc::new(HarvestMemoryFromTurn::new(
                 Arc::clone(&memory_store_port),
                 Arc::clone(&events_port),
-            ))),
+            )))
+            // Outil MCP `idea_skill_read` (feature « skills à la MCP ») : sans ça,
+            // `skill.read` renverrait « not configured ». Compose le SkillStore existant.
+            .with_read_skill(Arc::clone(&read_skill)),
             // NB (régression corrigée) : on ne câble PAS `.with_structured(...)` ici.
             // Décision produit lot B-2 (« Option 1 Terminal + MCP », cf. construction
             // de `LaunchAgent` plus haut) : la fabrique structurée est décâblée, donc

crates/application/src/agent/lifecycle.rs

@@ -2542,16 +2542,25 @@ fn append_block(input: &str, block: &str) -> String {
 /// `# Skills` section (ARCHITECTURE §14.2).
 ///
 /// A short skill-awareness paragraph is always injected in the orchestration
-/// block: it explains that assigned skills are operational workflow context, not
-/// magic commands or provider subagents, and points reusable workflow creation to
-/// the active IdeA orchestration surface (`idea_create_skill` for MCP profiles,
-/// `skill.create` for the file protocol). This awareness deliberately does not
-/// inject unassigned skill bodies; assignment remains the context boundary.
+/// block (followed by the auto-memory harvest directive, Lot E1): it explains that
+/// assigned skills are operational workflow context, not magic commands or provider
+/// subagents, and points reusable workflow creation to the active IdeA orchestration
+/// surface (`idea_create_skill` for MCP profiles, `skill.create` for the file
+/// protocol). This awareness deliberately does not inject unassigned skill bodies;
+/// assignment remains the context boundary.
 ///
-/// Skills are emitted in the order given (the caller passes them in manifest
-/// order, making the output deterministic); each is introduced by a `##` header
-/// carrying its name. When `skills` is empty the section is omitted entirely, so
-/// an agent with no skills gets exactly the previous document.
+/// On top of that awareness, the assigned skills surface in one of two ways
+/// depending on the agent's **surface** (feature « skills à la MCP »), always in
+/// the given (manifest) order — making the output deterministic:
+/// - **MCP mode** (`mcp_enabled`): a high-altitude `# Skills disponibles` section,
+///   right after the orchestration block, listing each as
+///   `**<name>** — <effective description>` (affordances only, *no body*), with
+///   prose pointing to `idea_skill_read` to load a body on demand. Respects the
+///   altitude: the capability is exposed, never the skill content.
+/// - **Non-MCP mode**: the legacy `# Skills` section dumping each body in full
+///   under a `##` header carrying its name (unchanged — zero regression).
+/// When `skills` is empty both sections are omitted entirely, so an agent with no
+/// skills gets exactly the previous document.
 ///
 /// The project's `memory` recall (index/hooks, ARCHITECTURE §14.5.4) is appended as
 /// a `# Mémoire projet` section — one `- [Title](slug.md) — hook (type)` line per
@@ -2627,6 +2636,29 @@ pub(crate) fn compose_convention_file(
     out.push_str(memory_awareness());
     out.push_str("---\n\n");
 
+    // Skills « à la MCP » (feature skill-awareness) : à HAUTE ALTITUDE, juste après
+    // le bloc d'orchestration. On expose les skills assignés comme des **affordances
+    // nommées+décrites** (et NON leur corps complet), à la manière des outils MCP,
+    // pour que l'agent sache qu'ils existent et charge le détail à la demande via
+    // `idea_skill_read`. Réservé au mode MCP (le mode sans MCP conserve l'ancien dump
+    // du corps complet en fin de fichier, plus bas). Omis si zéro skill.
+    if mcp_enabled && !skills.is_empty() {
+        out.push_str("# Skills disponibles\n\n");
+        out.push_str(
+            "Les skills suivants te sont assignés. Pour en exécuter un ou consulter son \
+             détail, appelle l'outil `idea_skill_read(name=…)` — n'improvise pas un \
+             workflow déjà couvert par un skill, charge-le.\n\n",
+        );
+        for skill in skills {
+            out.push_str("**");
+            out.push_str(&skill.name);
+            out.push_str("** — ");
+            out.push_str(&skill.effective_description());
+            out.push('\n');
+        }
+        out.push_str("\n---\n\n");
+    }
+
     if !project_context.trim().is_empty() {
         out.push_str("# Contexte projet\n\n");
         out.push_str(project_context.trim());
@@ -2635,7 +2667,11 @@ pub(crate) fn compose_convention_file(
 
     out.push_str(agent_md);
 
-    if !skills.is_empty() {
+    // MODE SANS MCP (exigence zéro régression, décision produit 4.2(b)) : on conserve
+    // l'ancien dump du **corps complet** des skills en fin de fichier. En mode MCP, le
+    // corps n'est PAS injecté ici (l'agent le charge à la demande via `idea_skill_read`,
+    // cf. la section « # Skills disponibles » à haute altitude plus haut).
+    if !skills.is_empty() && !mcp_enabled {
         out.push_str("\n\n---\n\n# Skills\n");
         for skill in skills {
             out.push_str("\n## ");
@@ -2944,6 +2980,65 @@ mod tests {
         );
     }
 
+    #[test]
+    fn compose_convention_file_mcp_mode_exposes_skill_affordances_not_bodies() {
+        // MCP mode (feature « skills à la MCP »): a high-altitude `# Skills disponibles`
+        // section after the Orchestration block, listing `**name** — description`
+        // affordances and pointing to `idea_skill_read`, WITHOUT dumping the bodies.
+        let s = |n: u128, name: &str, desc: Option<&str>, body: &str| {
+            Skill::new(
+                domain::SkillId::from_uuid(uuid::Uuid::from_u128(n)),
+                name,
+                MarkdownDoc::new(body),
+                domain::SkillScope::Global,
+            )
+            .unwrap()
+            .with_description(desc.map(str::to_owned))
+        };
+        let doc = compose_convention_file(
+            "/root",
+            "",
+            "# Persona",
+            &[
+                s(1, "refactor", Some("Refactors code"), "REFAC_BODY"),
+                // No explicit description ⇒ effective_description falls back to the
+                // body's first line (heading marker stripped).
+                s(2, "review", None, "# Review skill\n\nREVIEW_BODY"),
+            ],
+            &[],
+            None,
+            true, // mcp_enabled
+        );
+
+        // The affordance section is present.
+        assert!(doc.contains("# Skills disponibles"), "MCP skills section present");
+        assert!(doc.contains("idea_skill_read"), "points to the read tool");
+        // Affordance lines: `**name** — <effective description>`.
+        assert!(doc.contains("**refactor** — Refactors code"));
+        assert!(doc.contains("**review** — Review skill"));
+        // The full bodies are NOT injected in MCP mode (loaded on demand instead).
+        assert!(!doc.contains("REFAC_BODY"), "no full body in MCP mode");
+        assert!(!doc.contains("REVIEW_BODY"), "no full body in MCP mode");
+        // The legacy `## <name>` body dump headers are absent too.
+        assert!(!doc.contains("## refactor"));
+
+        // The section sits at high altitude: after the Orchestration block, before
+        // the persona.
+        let orch_at = doc.find("# Orchestration IdeA").unwrap();
+        let skills_at = doc.find("# Skills disponibles").unwrap();
+        let persona_at = doc.find("# Persona").unwrap();
+        assert!(orch_at < skills_at, "skills come after orchestration");
+        assert!(skills_at < persona_at, "skills come before the persona");
+    }
+
+    #[test]
+    fn compose_convention_file_mcp_mode_without_skills_omits_section() {
+        // MCP mode + zero skills ⇒ no `# Skills disponibles` section at all.
+        let doc = compose_convention_file("/root", "", "# Persona", &[], &[], None, true);
+        assert!(!doc.contains("# Skills disponibles"));
+        assert!(!doc.contains("idea_skill_read"));
+    }
+
     /// Builds a memory index entry for the convention-file composition tests.
     fn mem(slug_str: &str, title: &str, hook: &str, kind: MemoryType) -> MemoryIndexEntry {
         MemoryIndexEntry {

crates/application/src/lib.rs

@@ -100,9 +100,9 @@ pub use project::{
 pub use remote::{ConnectRemote, ConnectRemoteInput, ConnectRemoteOutput};
 pub use skill::{
     AssignSkillToAgent, AssignSkillToAgentInput, CreateSkill, CreateSkillInput, CreateSkillOutput,
-    DeleteSkill, DeleteSkillInput, ListSkills, ListSkillsInput, ListSkillsOutput,
-    UnassignSkillFromAgent, UnassignSkillFromAgentInput, UpdateSkill, UpdateSkillInput,
-    UpdateSkillOutput,
+    DeleteSkill, DeleteSkillInput, ListSkills, ListSkillsInput, ListSkillsOutput, ReadSkill,
+    ReadSkillInput, UnassignSkillFromAgent, UnassignSkillFromAgentInput, UpdateSkill,
+    UpdateSkillInput, UpdateSkillOutput,
 };
 pub use template::{
     AgentDrift, CreateAgentFromTemplate, CreateAgentFromTemplateInput,

crates/application/src/orchestrator/service.rs

@@ -43,7 +43,7 @@ use crate::orchestrator::{
     ProposeContext, ProposeContextInput, ProposeOutcome, ReadContext, ReadContextInput, ReadMemory,
     ReadMemoryInput, WriteMemory, WriteMemoryInput,
 };
-use crate::skill::{CreateSkill, CreateSkillInput};
+use crate::skill::{CreateSkill, CreateSkillInput, ReadSkill, ReadSkillInput};
 use crate::terminal::{CloseTerminal, CloseTerminalInput, StructuredSessions, TerminalSessions};
 
 /// Default terminal geometry for an orchestrator-launched agent cell. The UI
@@ -303,6 +303,11 @@ pub struct OrchestratorService {
     /// [`Self::with_memory_harvest`] ; `None` ⇒ aucun harvest (zéro régression). Un
     /// échec de harvest ne transforme **jamais** un succès de délégation en erreur.
     memory_harvest: Option<Arc<HarvestMemoryFromTurn>>,
+    /// Use case de lecture d'un skill **par nom** (`idea_skill_read`, feature
+    /// « skills à la MCP »). Compose le port `SkillStore` existant (aucun nouveau
+    /// port). Injecté via [`Self::with_read_skill`] ; `None` ⇒ la commande
+    /// `skill.read` renvoie une erreur typée (call sites/tests legacy restent verts).
+    read_skill: Option<Arc<ReadSkill>>,
 }
 
 /// Bundle des quatre use cases C7 sous [`domain::fileguard::FileGuard`], injectés
@@ -367,9 +372,19 @@ impl OrchestratorService {
             clock: None,
             structured: None,
             memory_harvest: None,
+            read_skill: None,
         }
     }
 
+    /// Branche le use case [`ReadSkill`] (`skill.read`/`idea_skill_read`). Builder
+    /// additif (signature de [`Self::new`] inchangée) ; `None` ⇒ la commande
+    /// renvoie une erreur typée « not configured ».
+    #[must_use]
+    pub fn with_read_skill(mut self, read_skill: Arc<ReadSkill>) -> Self {
+        self.read_skill = Some(read_skill);
+        self
+    }
+
     /// Branche le registre des [`StructuredSessions`] (§17.5) pour router un `ask`
     /// vers une cible **structurée** sur sa propre session. Builder additif (signature
     /// de [`Self::new`] inchangée) ; `None` ⇒ chemin PTY/mailbox legacy uniquement.
@@ -588,6 +603,9 @@ impl OrchestratorService {
             OrchestratorCommand::ReadMemory { slug, requester } => {
                 self.read_memory(project, slug, requester).await
             }
+            OrchestratorCommand::ReadSkill { name, requester } => {
+                self.read_skill(project, name, requester).await
+            }
             OrchestratorCommand::WriteMemory {
                 slug,
                 content,
@@ -682,6 +700,31 @@ impl OrchestratorService {
         })
     }
 
+    /// `skill.read` → resolves a skill by name (project scope first, then global)
+    /// and returns its Markdown body inline in the outcome's `reply`. Read-only:
+    /// `requester` is accepted for symmetry with the other read tools but skill
+    /// reads take no [`domain::fileguard::FileGuard`] lease.
+    async fn read_skill(
+        &self,
+        project: &Project,
+        name: String,
+        _requester: ConversationParty,
+    ) -> Result<OrchestratorOutcome, AppError> {
+        let read_skill = self.read_skill.as_deref().ok_or_else(|| {
+            AppError::Invalid("the idea_skill_read tool is not configured".to_owned())
+        })?;
+        let md = read_skill
+            .execute(ReadSkillInput {
+                name: name.clone(),
+                project_root: project.root.clone(),
+            })
+            .await?;
+        Ok(OrchestratorOutcome {
+            detail: format!("read skill {name}"),
+            reply: Some(md.into_string()),
+        })
+    }
+
     /// `memory.write` → writes a note under an exclusive write-lease.
     async fn write_memory(
         &self,
@@ -1867,6 +1910,9 @@ impl OrchestratorService {
             .create_skill
             .execute(CreateSkillInput {
                 name: name.clone(),
+                // `idea_create_skill` carries no description argument; the affordance
+                // falls back to the body's first line (see `effective_description`).
+                description: None,
                 content,
                 scope,
                 project_root: project.root.clone(),

crates/application/src/skill/mod.rs

@@ -15,7 +15,7 @@ mod usecases;
 
 pub use usecases::{
     AssignSkillToAgent, AssignSkillToAgentInput, CreateSkill, CreateSkillInput, CreateSkillOutput,
-    DeleteSkill, DeleteSkillInput, ListSkills, ListSkillsInput, ListSkillsOutput,
-    UnassignSkillFromAgent, UnassignSkillFromAgentInput, UpdateSkill, UpdateSkillInput,
-    UpdateSkillOutput,
+    DeleteSkill, DeleteSkillInput, ListSkills, ListSkillsInput, ListSkillsOutput, ReadSkill,
+    ReadSkillInput, UnassignSkillFromAgent, UnassignSkillFromAgentInput, UpdateSkill,
+    UpdateSkillInput, UpdateSkillOutput,
 };

crates/application/src/skill/usecases.rs

@@ -25,6 +25,10 @@ use crate::error::AppError;
 pub struct CreateSkillInput {
     /// Display name (also the `.md` stem on disk).
     pub name: String,
+    /// Optional one-line affordance description (feature « skills à la MCP »).
+    /// `None`/empty ⇒ the skill falls back to the first line of its body when
+    /// surfaced (see [`domain::Skill::effective_description`]).
+    pub description: Option<String>,
     /// Initial Markdown body.
     pub content: String,
     /// Scope the skill is created in (selects its backing store).
@@ -61,7 +65,8 @@ impl CreateSkill {
     pub async fn execute(&self, input: CreateSkillInput) -> Result<CreateSkillOutput, AppError> {
         let id = SkillId::from_uuid(self.ids.new_uuid());
         let skill = Skill::new(id, input.name, MarkdownDoc::new(input.content), input.scope)
-            .map_err(|e| AppError::Invalid(e.to_string()))?;
+            .map_err(|e| AppError::Invalid(e.to_string()))?
+            .with_description(input.description);
         self.skills.save(&skill, &input.project_root).await?;
         Ok(CreateSkillOutput { skill })
     }
@@ -204,6 +209,77 @@ impl DeleteSkill {
     }
 }
 
+// ---------------------------------------------------------------------------
+// ReadSkill
+// ---------------------------------------------------------------------------
+
+/// Input for [`ReadSkill::execute`].
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct ReadSkillInput {
+    /// Skill display name to resolve (case-insensitive).
+    pub name: String,
+    /// Active project root (used for the [`SkillScope::Project`] lookup).
+    pub project_root: ProjectPath,
+}
+
+/// Reads a skill's Markdown body **by name** — the application side of the MCP
+/// `idea_skill_read` tool (feature « skills à la MCP »).
+///
+/// Resolution follows the affordance contract: **project scope first, then
+/// global** (a project skill shadows a global one of the same name). It composes
+/// the **existing** [`SkillStore`] port only — no new port. Read-only.
+pub struct ReadSkill {
+    skills: Arc<dyn SkillStore>,
+}
+
+impl ReadSkill {
+    /// Builds the use case from the existing skill store port.
+    #[must_use]
+    pub fn new(skills: Arc<dyn SkillStore>) -> Self {
+        Self { skills }
+    }
+
+    /// Resolves `name` in `scope`, returning the single match.
+    ///
+    /// `Ok(None)` ⇒ no skill by that name in this scope; `Err(Invalid)` ⇒ the
+    /// name is **ambiguous** (more than one skill shares it in this scope).
+    async fn resolve_in(
+        &self,
+        scope: SkillScope,
+        input: &ReadSkillInput,
+    ) -> Result<Option<Skill>, AppError> {
+        let all = self.skills.list(scope, &input.project_root).await?;
+        let mut matches = all
+            .into_iter()
+            .filter(|s| s.name.eq_ignore_ascii_case(&input.name));
+        match (matches.next(), matches.next()) {
+            (None, _) => Ok(None),
+            (Some(skill), None) => Ok(Some(skill)),
+            (Some(_), Some(_)) => Err(AppError::Invalid(format!(
+                "skill name `{}` is ambiguous in {scope:?} scope (several skills share it)",
+                input.name
+            ))),
+        }
+    }
+
+    /// Resolves the skill by name and returns its Markdown body.
+    ///
+    /// # Errors
+    /// - [`AppError::Invalid`] if the name is ambiguous within a scope,
+    /// - [`AppError::NotFound`] if no skill carries that name in either scope,
+    /// - [`AppError::Store`] on a store failure.
+    pub async fn execute(&self, input: ReadSkillInput) -> Result<MarkdownDoc, AppError> {
+        // Project scope shadows global: try it first, then fall back to global.
+        if let Some(skill) = self.resolve_in(SkillScope::Project, &input).await? {
+            return Ok(skill.content_md);
+        }
+        if let Some(skill) = self.resolve_in(SkillScope::Global, &input).await? {
+            return Ok(skill.content_md);
+        }
+        Err(AppError::NotFound(format!("skill `{}`", input.name)))
+    }
+}
+
 // ---------------------------------------------------------------------------
 // AssignSkillToAgent / UnassignSkillFromAgent
 // ---------------------------------------------------------------------------
@@ -349,3 +425,185 @@ impl UnassignSkillFromAgent {
         Ok(())
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::sync::Mutex;
+
+    use async_trait::async_trait;
+    use domain::ports::{SkillStore, StoreError};
+
+    /// In-memory [`SkillStore`] fake: skills are bucketed by scope, ignoring the
+    /// project root (the [`ReadSkill`] resolution logic is root-agnostic — it only
+    /// switches scope). Enough to exercise project-first resolution, shadowing,
+    /// ambiguity and absence without touching disk.
+    #[derive(Default)]
+    struct FakeSkillStore {
+        global: Mutex<Vec<Skill>>,
+        project: Mutex<Vec<Skill>>,
+    }
+
+    impl FakeSkillStore {
+        fn bucket(&self, scope: SkillScope) -> &Mutex<Vec<Skill>> {
+            match scope {
+                SkillScope::Global => &self.global,
+                SkillScope::Project => &self.project,
+            }
+        }
+
+        fn push(&self, skill: Skill) {
+            self.bucket(skill.scope).lock().unwrap().push(skill);
+        }
+    }
+
+    #[async_trait]
+    impl SkillStore for FakeSkillStore {
+        async fn list(
+            &self,
+            scope: SkillScope,
+            _root: &ProjectPath,
+        ) -> Result<Vec<Skill>, StoreError> {
+            Ok(self.bucket(scope).lock().unwrap().clone())
+        }
+        async fn get(
+            &self,
+            scope: SkillScope,
+            _root: &ProjectPath,
+            id: SkillId,
+        ) -> Result<Skill, StoreError> {
+            self.bucket(scope)
+                .lock()
+                .unwrap()
+                .iter()
+                .find(|s| s.id == id)
+                .cloned()
+                .ok_or(StoreError::NotFound)
+        }
+        async fn save(&self, skill: &Skill, _root: &ProjectPath) -> Result<(), StoreError> {
+            self.push(skill.clone());
+            Ok(())
+        }
+        async fn delete(
+            &self,
+            _scope: SkillScope,
+            _root: &ProjectPath,
+            _id: SkillId,
+        ) -> Result<(), StoreError> {
+            Ok(())
+        }
+    }
+
+    fn root() -> ProjectPath {
+        ProjectPath::new("/proj").unwrap()
+    }
+
+    fn skill(id: u128, name: &str, body: &str, scope: SkillScope) -> Skill {
+        Skill::new(
+            SkillId::from_uuid(uuid::Uuid::from_u128(id)),
+            name,
+            MarkdownDoc::new(body),
+            scope,
+        )
+        .unwrap()
+    }
+
+    fn read_skill_uc(store: Arc<FakeSkillStore>) -> ReadSkill {
+        ReadSkill::new(store)
+    }
+
+    #[tokio::test]
+    async fn read_skill_resolves_project_scope() {
+        // (a) skill present in the project scope ⇒ its body is returned.
+        let store = Arc::new(FakeSkillStore::default());
+        store.push(skill(1, "deploy", "PROJECT_BODY", SkillScope::Project));
+
+        let body = read_skill_uc(store)
+            .execute(ReadSkillInput {
+                name: "deploy".to_owned(),
+                project_root: root(),
+            })
+            .await
+            .unwrap();
+        assert_eq!(body.as_str(), "PROJECT_BODY");
+    }
+
+    #[tokio::test]
+    async fn read_skill_falls_back_to_global_scope() {
+        // (b) absent from project but present globally ⇒ resolved via global.
+        let store = Arc::new(FakeSkillStore::default());
+        store.push(skill(1, "deploy", "GLOBAL_BODY", SkillScope::Global));
+
+        let body = read_skill_uc(store)
+            .execute(ReadSkillInput {
+                name: "deploy".to_owned(),
+                project_root: root(),
+            })
+            .await
+            .unwrap();
+        assert_eq!(body.as_str(), "GLOBAL_BODY");
+    }
+
+    #[tokio::test]
+    async fn read_skill_project_shadows_global() {
+        // (c) same name in both scopes ⇒ project wins.
+        let store = Arc::new(FakeSkillStore::default());
+        store.push(skill(1, "deploy", "GLOBAL_BODY", SkillScope::Global));
+        store.push(skill(2, "deploy", "PROJECT_BODY", SkillScope::Project));
+
+        let body = read_skill_uc(store)
+            .execute(ReadSkillInput {
+                name: "deploy".to_owned(),
+                project_root: root(),
+            })
+            .await
+            .unwrap();
+        assert_eq!(body.as_str(), "PROJECT_BODY");
+    }
+
+    #[tokio::test]
+    async fn read_skill_is_case_insensitive() {
+        let store = Arc::new(FakeSkillStore::default());
+        store.push(skill(1, "Deploy", "BODY", SkillScope::Project));
+
+        let body = read_skill_uc(store)
+            .execute(ReadSkillInput {
+                name: "deploy".to_owned(),
+                project_root: root(),
+            })
+            .await
+            .unwrap();
+        assert_eq!(body.as_str(), "BODY");
+    }
+
+    #[tokio::test]
+    async fn read_skill_unknown_is_not_found() {
+        // (d) unknown in both scopes ⇒ NotFound.
+        let store = Arc::new(FakeSkillStore::default());
+        let err = read_skill_uc(store)
+            .execute(ReadSkillInput {
+                name: "ghost".to_owned(),
+                project_root: root(),
+            })
+            .await
+            .unwrap_err();
+        assert!(matches!(err, AppError::NotFound(_)), "got {err:?}");
+    }
+
+    #[tokio::test]
+    async fn read_skill_ambiguous_name_is_invalid() {
+        // (e) two skills share a name within a scope ⇒ Invalid (ambiguous).
+        let store = Arc::new(FakeSkillStore::default());
+        store.push(skill(1, "deploy", "ONE", SkillScope::Project));
+        store.push(skill(2, "Deploy", "TWO", SkillScope::Project));
+
+        let err = read_skill_uc(store)
+            .execute(ReadSkillInput {
+                name: "deploy".to_owned(),
+                project_root: root(),
+            })
+            .await
+            .unwrap_err();
+        assert!(matches!(err, AppError::Invalid(_)), "got {err:?}");
+    }
+}

crates/application/tests/skill_usecases.rs

@@ -195,6 +195,7 @@ async fn create_skill_persists_in_its_scope() {
     let out = CreateSkill::new(Arc::new(store.clone()), Arc::new(SeqIds::new()))
         .execute(CreateSkillInput {
             name: "refactor".to_owned(),
+            description: Some("Refactors code".to_owned()),
             content: "# body".to_owned(),
             scope: SkillScope::Project,
             project_root: root(),
@@ -203,6 +204,8 @@ async fn create_skill_persists_in_its_scope() {
         .unwrap();
 
     assert_eq!(out.skill.scope, SkillScope::Project);
+    // The one-line affordance description flows through the use case onto the skill.
+    assert_eq!(out.skill.description.as_deref(), Some("Refactors code"));
     assert_eq!(
         store
             .list(SkillScope::Project, &root())
@@ -224,6 +227,7 @@ async fn create_skill_rejects_empty_content() {
     let err = CreateSkill::new(Arc::new(store), Arc::new(SeqIds::new()))
         .execute(CreateSkillInput {
             name: "k".to_owned(),
+            description: None,
             content: String::new(),
             scope: SkillScope::Global,
             project_root: root(),

crates/domain/src/orchestrator.rs

@@ -248,6 +248,17 @@ pub enum OrchestratorCommand {
         /// The reading party (handshake identity).
         requester: ConversationParty,
     },
+    /// Read a reusable skill's Markdown body **by name** (`idea_skill_read`,
+    /// feature « skills à la MCP »). Resolution is project-scope-first then global;
+    /// the body is returned inline. Read-only — no [`crate::fileguard::FileGuard`]
+    /// lease (skills are not mutated through this path).
+    ReadSkill {
+        /// Skill display name to resolve (case-insensitive).
+        name: String,
+        /// The party that issued the read (handshake identity). Carried for
+        /// symmetry/auditing with the other read tools; skill reads need no lease.
+        requester: ConversationParty,
+    },
     /// Write a memory note under the [`crate::fileguard::FileGuard`] (cadrage C7).
     /// Memory is project-shared; written directly under a write-lease.
     WriteMemory {
@@ -345,6 +356,10 @@ impl OrchestratorRequest {
                 slug: self.optional_slug(),
                 requester: self.requester_party(),
             }),
+            "skill.read" => Ok(OrchestratorCommand::ReadSkill {
+                name: self.require_name(action)?,
+                requester: self.requester_party(),
+            }),
             "memory.write" => Ok(OrchestratorCommand::WriteMemory {
                 slug: self.require("slug", action, self.slug.as_deref())?,
                 content: self.require("content", action, self.content.as_deref())?,

crates/domain/src/skill.rs

@@ -39,6 +39,12 @@ pub struct Skill {
     pub id: SkillId,
     /// Display name (also used as the `.md` file stem on disk).
     pub name: String,
+    /// Optional one-line description surfaced as an *affordance* at high altitude
+    /// in an agent's convention file (« à la MCP »), so the agent knows the skill
+    /// exists and what it does without reading the whole body. `None`/empty ⇒
+    /// [`Skill::effective_description`] falls back to the first line of the body.
+    #[serde(default)]
+    pub description: Option<String>,
     /// Markdown body — the workflow injected into an agent's convention file.
     pub content_md: MarkdownDoc,
     /// Scope (selects the backing store).
@@ -67,18 +73,57 @@ impl Skill {
         Ok(Self {
             id,
             name,
+            description: None,
             content_md,
             scope,
         })
     }
 
+    /// Returns this skill with its one-line [`Skill::description`] set (builder).
+    ///
+    /// Kept separate from [`Skill::new`] so every existing call site is untouched
+    /// (the field is purely additive). An empty/whitespace description is treated
+    /// as absent by [`Skill::effective_description`], so no normalisation here.
+    #[must_use]
+    pub fn with_description(mut self, description: Option<String>) -> Self {
+        self.description = description;
+        self
+    }
+
+    /// The description to surface for this skill, with a deterministic fallback.
+    ///
+    /// Returns [`Skill::description`] when present and non-blank (trimmed);
+    /// otherwise the **first non-empty line** of the body, stripped of any leading
+    /// `#` (Markdown heading marker) and trimmed. When the body has no usable line
+    /// either, returns an **empty `String`** (chosen over `Option` so callers can
+    /// format it unconditionally — an empty affordance line is harmless).
+    #[must_use]
+    pub fn effective_description(&self) -> String {
+        if let Some(desc) = &self.description {
+            let trimmed = desc.trim();
+            if !trimmed.is_empty() {
+                return trimmed.to_owned();
+            }
+        }
+        self.content_md
+            .as_str()
+            .lines()
+            .map(str::trim)
+            .find(|line| !line.is_empty())
+            .map(|line| line.trim_start_matches('#').trim().to_owned())
+            .unwrap_or_default()
+    }
+
     /// Returns a copy of this skill with replaced content, re-validating the
-    /// non-empty invariant.
+    /// non-empty invariant and **preserving** the [`Skill::description`].
     ///
     /// # Errors
     /// [`DomainError::EmptyField`] if `content_md` is empty.
     pub fn with_content(&self, content_md: MarkdownDoc) -> Result<Self, DomainError> {
-        Skill::new(self.id, self.name.clone(), content_md, self.scope)
+        Ok(
+            Skill::new(self.id, self.name.clone(), content_md, self.scope)?
+                .with_description(self.description.clone()),
+        )
     }
 }
 
@@ -109,3 +154,98 @@ impl From<&Skill> for SkillRef {
         Self::new(skill.id, skill.scope)
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::ids::SkillId;
+
+    fn skill(body: &str) -> Skill {
+        Skill::new(
+            SkillId::from_uuid(uuid::Uuid::from_u128(1)),
+            "demo",
+            MarkdownDoc::new(body),
+            SkillScope::Global,
+        )
+        .unwrap()
+    }
+
+    // -- effective_description --------------------------------------------
+
+    #[test]
+    fn effective_description_returns_explicit_description_trimmed() {
+        // (a) explicit non-empty description ⇒ returned trimmed.
+        let s = skill("# Heading\n\nbody").with_description(Some("  Refactors code  ".to_owned()));
+        assert_eq!(s.effective_description(), "Refactors code");
+    }
+
+    #[test]
+    fn effective_description_falls_back_to_first_body_line_without_hash() {
+        // (b) description None ⇒ first non-empty body line, `#` stripped & trimmed.
+        let s = skill("\n\n#   My Skill Title  \n\nrest of body");
+        assert_eq!(s.effective_description(), "My Skill Title");
+    }
+
+    #[test]
+    fn effective_description_first_line_without_heading_marker() {
+        // (b') first non-empty line that is not a heading is returned verbatim (trimmed).
+        let s = skill("  just a plain first line\nsecond");
+        assert_eq!(s.effective_description(), "just a plain first line");
+    }
+
+    #[test]
+    fn effective_description_blank_body_yields_empty_string() {
+        // (c) body that is only whitespace ⇒ empty String.
+        let s = skill("   \n\t\n   ");
+        assert_eq!(s.effective_description(), "");
+    }
+
+    #[test]
+    fn effective_description_blank_description_falls_back_to_body() {
+        // (d) description Some("") / whitespace-only ⇒ treated as absent ⇒ body fallback.
+        let empty = skill("# Body Heading").with_description(Some(String::new()));
+        assert_eq!(empty.effective_description(), "Body Heading");
+
+        let spaces = skill("# Body Heading").with_description(Some("   \t  ".to_owned()));
+        assert_eq!(spaces.effective_description(), "Body Heading");
+    }
+
+    // -- with_content preserves description -------------------------------
+
+    #[test]
+    fn with_content_preserves_description() {
+        let s = skill("old body").with_description(Some("kept".to_owned()));
+        let updated = s.with_content(MarkdownDoc::new("new body")).unwrap();
+        assert_eq!(updated.description.as_deref(), Some("kept"));
+        assert_eq!(updated.content_md.as_str(), "new body");
+    }
+
+    #[test]
+    fn with_content_rejects_empty_body() {
+        let s = skill("old body");
+        assert!(s.with_content(MarkdownDoc::new("")).is_err());
+    }
+
+    // -- serde: description is additive / defaults to None ----------------
+
+    #[test]
+    fn deserialize_legacy_skill_without_description_defaults_to_none() {
+        // A skill JSON written before `description` existed must deserialise with
+        // `description: None` thanks to `#[serde(default)]`.
+        let id = uuid::Uuid::from_u128(7);
+        let json =
+            format!(r##"{{"id":"{id}","name":"legacy","contentMd":"# body","scope":"global"}}"##);
+        let parsed: Skill = serde_json::from_str(&json).unwrap();
+        assert_eq!(parsed.description, None);
+        assert_eq!(parsed.name, "legacy");
+    }
+
+    #[test]
+    fn serde_round_trip_with_description() {
+        let original = skill("# body").with_description(Some("affordance".to_owned()));
+        let json = serde_json::to_string(&original).unwrap();
+        let back: Skill = serde_json::from_str(&json).unwrap();
+        assert_eq!(back, original);
+        assert_eq!(back.description.as_deref(), Some("affordance"));
+    }
+}

crates/infrastructure/src/orchestrator/mcp/tools.rs

@@ -51,7 +51,11 @@ pub enum ToolMapError {
 pub fn tool_returns_reply(tool: &str) -> bool {
     matches!(
         tool,
-        "idea_ask_agent" | "idea_list_agents" | "idea_context_read" | "idea_memory_read"
+        "idea_ask_agent"
+            | "idea_list_agents"
+            | "idea_context_read"
+            | "idea_memory_read"
+            | "idea_skill_read"
     )
 }
 
@@ -201,6 +205,21 @@ pub fn catalogue() -> Vec<ToolDef> {
                 "additionalProperties": false
             }),
         },
+        ToolDef {
+            name: "idea_skill_read",
+            description: "Read the full body of an IdeA skill assigned to you, by name — call this \
+                          to actually execute/follow a skill listed in your « Skills disponibles » \
+                          section. Resolves project scope first, then global. Returns the skill's \
+                          Markdown inline.",
+            input_schema: json!({
+                "type": "object",
+                "properties": {
+                    "name": { "type": "string", "description": "Skill name (as listed in your context)." }
+                },
+                "required": ["name"],
+                "additionalProperties": false
+            }),
+        },
         ToolDef {
             name: "idea_create_skill",
             description: "Create a reusable IdeA skill (Markdown) in the project or global scope.",
@@ -320,6 +339,14 @@ pub fn map_tool_call(
             content: s("content"),
             ..base()
         },
+        "idea_skill_read" => OrchestratorRequest {
+            request_type: Some("skill.read".to_owned()),
+            // The requester (handshake identity) is carried for symmetry with the
+            // other read tools; `validate` derives the requester party from it.
+            requested_by: Some(requester.to_owned()),
+            name: s("name"),
+            ..base()
+        },
         "idea_create_skill" => OrchestratorRequest {
             request_type: Some("skill.create".to_owned()),
             name: s("name"),

crates/infrastructure/src/store/skill.rs

@@ -58,6 +58,11 @@ const INDEX_VERSION: u32 = 1;
 struct IndexEntry {
     id: SkillId,
     name: String,
+    /// One-line affordance description (feature « skills à la MCP »). `#[serde(default)]`
+    /// is **mandatory** for backward-compat: legacy `index.json` written before this
+    /// field existed deserialise with `None` instead of failing.
+    #[serde(default)]
+    description: Option<String>,
     content_hash: String,
 }
 
@@ -189,6 +194,7 @@ impl FsSkillStore {
             MarkdownDoc::new(content),
             scope,
         )
+        .map(|skill| skill.with_description(entry.description.clone()))
         .map_err(|e| StoreError::Serialization(e.to_string()))
     }
 }
@@ -239,6 +245,7 @@ impl SkillStore for FsSkillStore {
         let row = IndexEntry {
             id: skill.id,
             name: skill.name.clone(),
+            description: skill.description.clone(),
             content_hash: content_hash(&skill.content_md),
         };
         if let Some(slot) = index.skills.iter_mut().find(|e| e.id == skill.id) {
@@ -266,3 +273,129 @@ impl SkillStore for FsSkillStore {
         self.write_index(scope, root, &index).await
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::collections::HashMap;
+    use std::sync::Mutex;
+
+    use domain::ports::{DirEntry, FsError};
+
+    /// In-memory [`FileSystem`] mock (same minimal shape as the memory-store tests).
+    #[derive(Default)]
+    struct MemFs {
+        files: Mutex<HashMap<String, Vec<u8>>>,
+    }
+
+    impl MemFs {
+        fn arc() -> Arc<Self> {
+            Arc::new(Self::default())
+        }
+    }
+
+    #[async_trait]
+    impl FileSystem for MemFs {
+        async fn read(&self, path: &RemotePath) -> Result<Vec<u8>, FsError> {
+            self.files
+                .lock()
+                .unwrap()
+                .get(path.as_str())
+                .cloned()
+                .ok_or_else(|| FsError::NotFound(path.as_str().to_string()))
+        }
+        async fn write(&self, path: &RemotePath, data: &[u8]) -> Result<(), FsError> {
+            self.files
+                .lock()
+                .unwrap()
+                .insert(path.as_str().to_string(), data.to_vec());
+            Ok(())
+        }
+        async fn exists(&self, path: &RemotePath) -> Result<bool, FsError> {
+            Ok(self.files.lock().unwrap().contains_key(path.as_str()))
+        }
+        async fn create_dir_all(&self, _path: &RemotePath) -> Result<(), FsError> {
+            Ok(())
+        }
+        async fn list(&self, _path: &RemotePath) -> Result<Vec<DirEntry>, FsError> {
+            Ok(Vec::new())
+        }
+        async fn symlink(&self, _src: &RemotePath, _dst: &RemotePath) -> Result<(), FsError> {
+            Ok(())
+        }
+    }
+
+    fn root() -> ProjectPath {
+        ProjectPath::new("/proj").unwrap()
+    }
+
+    fn skill(id: u128, name: &str, body: &str) -> Skill {
+        Skill::new(
+            SkillId::from_uuid(uuid::Uuid::from_u128(id)),
+            name,
+            MarkdownDoc::new(body),
+            SkillScope::Global,
+        )
+        .unwrap()
+    }
+
+    #[tokio::test]
+    async fn legacy_index_without_description_loads_with_none() {
+        // A legacy `index.json` written before the `description` field existed must
+        // deserialise (thanks to `#[serde(default)]`) and load with `description: None`.
+        let fs = MemFs::arc();
+        let id = uuid::Uuid::from_u128(42);
+        let legacy_index = format!(
+            r#"{{"version":1,"skills":[{{"id":"{id}","name":"legacy","contentHash":"abc"}}]}}"#
+        );
+        fs.write(
+            &RemotePath::new("/app/skills/index.json".to_owned()),
+            legacy_index.as_bytes(),
+        )
+        .await
+        .unwrap();
+        fs.write(
+            &RemotePath::new(format!("/app/skills/md/{id}.md")),
+            b"# legacy body",
+        )
+        .await
+        .unwrap();
+
+        let store = FsSkillStore::new(fs, "/app");
+        let listed = store.list(SkillScope::Global, &root()).await.unwrap();
+
+        assert_eq!(listed.len(), 1);
+        assert_eq!(listed[0].name, "legacy");
+        assert_eq!(listed[0].description, None);
+        assert_eq!(listed[0].content_md.as_str(), "# legacy body");
+    }
+
+    #[tokio::test]
+    async fn save_then_load_round_trips_description() {
+        let store = FsSkillStore::new(MemFs::arc(), "/app");
+        let s = skill(1, "refactor", "# Refactor\n\nbody")
+            .with_description(Some("Refactors code".to_owned()));
+
+        store.save(&s, &root()).await.unwrap();
+
+        let got = store.get(SkillScope::Global, &root(), s.id).await.unwrap();
+        assert_eq!(got.description.as_deref(), Some("Refactors code"));
+        assert_eq!(got, s);
+
+        // Also surfaces through `list`.
+        let listed = store.list(SkillScope::Global, &root()).await.unwrap();
+        assert_eq!(listed.len(), 1);
+        assert_eq!(listed[0].description.as_deref(), Some("Refactors code"));
+    }
+
+    #[tokio::test]
+    async fn save_without_description_loads_as_none() {
+        let store = FsSkillStore::new(MemFs::arc(), "/app");
+        let s = skill(2, "plain", "# Plain\n\nbody");
+
+        store.save(&s, &root()).await.unwrap();
+
+        let got = store.get(SkillScope::Global, &root(), s.id).await.unwrap();
+        assert_eq!(got.description, None);
+    }
+}

crates/infrastructure/tests/mcp_server.rs

@@ -506,6 +506,8 @@ async fn tools_list_advertises_the_seven_idea_tools_with_schemas() {
         "idea_stop_agent",
         "idea_update_context",
         "idea_create_skill",
+        // Read a skill's body by name (feature « skills à la MCP », T6).
+        "idea_skill_read",
         // FileGuard-mediated context/memory tools (cadrage C7).
         "idea_context_read",
         "idea_context_propose",
@@ -519,8 +521,8 @@ async fn tools_list_advertises_the_seven_idea_tools_with_schemas() {
     }
     assert_eq!(
         tools.len(),
-        11,
-        "exactly the eleven idea_* tools (7 base + 4 FileGuard C7); got {names:?}"
+        12,
+        "exactly the twelve idea_* tools (7 base + idea_skill_read + 4 FileGuard C7); got {names:?}"
     );
 
     // Every tool advertises an object input schema.