feat(FN-1511): apply skill selection to reviewer, merger, and heartbeat sessions

packages/engine/src/agent-heartbeat.ts

@@ -905,6 +905,7 @@ export class HeartbeatMonitor {
 
         // Lazy-load createKbAgent and promptWithFallback
         const { createKbAgent, promptWithFallback } = await import("./pi.js");
+        const { buildSessionSkillContextSync } = await import("./session-skill-context.js");
 
         // Build tools with task creation tracking and run context for mutation correlation
         const heartbeatTools = this.createHeartbeatTools(agentId, taskStore, taskId, runContext, audit);
@@ -916,6 +917,9 @@ export class HeartbeatMonitor {
           agent: agent.role as AgentRole,
         });
 
+        // Build skill selection context for heartbeat session (uses waking agent's skills, no role fallback)
+        const skillContext = buildSessionSkillContextSync(agent, "heartbeat", rootDir);
+
         // Create agent session
         const { session } = await createKbAgent({
           cwd: rootDir,
@@ -939,6 +943,8 @@ export class HeartbeatMonitor {
             toolCallCount++;
             agentLogger?.onToolEnd(name, isError, result);
           },
+          // Skill selection: use waking agent's skills (heartbeat has no role fallback)
+          ...(skillContext.skillSelectionContext ? { skillSelection: skillContext.skillSelectionContext } : {}),
         });
 
         // Track for monitoring

packages/engine/src/executor.ts

@@ -2339,6 +2339,7 @@ export class TaskExecutor {
               validatorFallbackModelId: settings.validatorFallbackModelId,
               store,
               taskId,
+              task: detail,
               agentPrompts: settings.agentPrompts,
               agentStore: this.options.agentStore,
               rootDir: this.rootDir,

packages/engine/src/merger.ts

@@ -7,6 +7,7 @@ import { join } from "node:path";
 import { getTaskMergeBlocker, type TaskStore, type MergeResult, type MergeDetails, type WorkflowStep, type WorkflowStepResult, type Settings, type AgentPromptsConfig } from "@fusion/core";
 import { resolveAgentPrompt } from "@fusion/core";
 import { createKbAgent, describeModel, promptWithFallback, compactSessionContext } from "./pi.js";
+import { buildSessionSkillContext } from "./session-skill-context.js";
 import type { WorktreePool } from "./worktree-pool.js";
 import { AgentLogger } from "./agent-logger.js";
 import { mergerLog } from "./logger.js";
@@ -2018,6 +2019,22 @@ async function runAiAgentForCommit(params: AiAgentParams): Promise<{ success: bo
     mergerInstructions,
   );
 
+  // Build skill selection context (assigned agent skills take precedence over role fallback)
+  let skillContext = undefined;
+  if (options.agentStore) {
+    try {
+      const task = await store.getTask(taskId);
+      skillContext = await buildSessionSkillContext({
+        agentStore: options.agentStore,
+        task,
+        sessionPurpose: "merger",
+        projectRootDir: rootDir,
+      });
+    } catch {
+      // Graceful fallback - no skill selection
+    }
+  }
+
   const { session } = await createKbAgent({
     cwd: rootDir,
     systemPrompt: mergerSystemPrompt,
@@ -2030,6 +2047,8 @@ async function runAiAgentForCommit(params: AiAgentParams): Promise<{ success: bo
     defaultProvider: settings.defaultProvider,
     defaultModelId: settings.defaultModelId,
     defaultThinkingLevel: settings.defaultThinkingLevel,
+    // Skill selection: use assigned agent skills if available, otherwise role fallback
+    ...(skillContext?.skillSelectionContext ? { skillSelection: skillContext.skillSelectionContext } : {}),
   });
 
   options.onSession?.(session);
@@ -2472,6 +2491,22 @@ If issues are found that need attention, describe them clearly.`;
     }
     const postMergeSystemPrompt = buildSystemPromptWithInstructions(systemPrompt, postMergeInstructions);
 
+    // Build skill selection context for post-merge session
+    let postMergeSkillContext = undefined;
+    if (mergeOptions.agentStore) {
+      try {
+        const task = await store.getTask(taskId);
+        postMergeSkillContext = await buildSessionSkillContext({
+          agentStore: mergeOptions.agentStore,
+          task,
+          sessionPurpose: "merger",
+          projectRootDir: rootDir,
+        });
+      } catch {
+        // Graceful fallback - no skill selection
+      }
+    }
+
     const { session } = await createKbAgent({
       cwd: rootDir,
       systemPrompt: postMergeSystemPrompt,
@@ -2481,6 +2516,8 @@ If issues are found that need attention, describe them clearly.`;
       fallbackProvider: settings.fallbackProvider,
       fallbackModelId: settings.fallbackModelId,
       defaultThinkingLevel: settings.defaultThinkingLevel,
+      // Skill selection: use assigned agent skills if available, otherwise role fallback
+      ...(postMergeSkillContext?.skillSelectionContext ? { skillSelection: postMergeSkillContext.skillSelectionContext } : {}),
     });
 
     mergerLog.log(`${taskId}: [post-merge] workflow step '${workflowStep.name}' using model ${describeModel(session)}${useOverride ? " (workflow step override)" : ""}`);

packages/engine/src/reviewer.ts

@@ -11,6 +11,7 @@
 import type { TaskStore, TaskComment, AgentPromptsConfig } from "@fusion/core";
 import { resolveAgentPrompt } from "@fusion/core";
 import { createKbAgent, describeModel, promptWithFallback } from "./pi.js";
+import { buildSessionSkillContext } from "./session-skill-context.js";
 import { AgentLogger } from "./agent-logger.js";
 import { reviewerLog } from "./logger.js";
 import { checkSessionError } from "./usage-limit-detector.js";
@@ -208,6 +209,8 @@ export interface ReviewOptions {
   store?: TaskStore;
   /** Task ID for agent log persistence. Required alongside `store`. */
   taskId?: string;
+  /** Task with optional assignedAgentId for skill selection. */
+  task?: { assignedAgentId?: string | null };
   /** User comments on the task (author === "user"). For spec reviews, the reviewer explicitly checks that every comment is addressed. */
   userComments?: TaskComment[];
   /** Agent prompt configuration for resolving custom reviewer prompts. */
@@ -283,6 +286,21 @@ export async function reviewStep(
     reviewerInstructions,
   );
 
+  // Build skill selection context (assigned agent skills take precedence over role fallback)
+  let skillContext = undefined;
+  if (options.agentStore && options.rootDir) {
+    try {
+      skillContext = await buildSessionSkillContext({
+        agentStore: options.agentStore,
+        task: options.task ?? {},
+        sessionPurpose: "reviewer",
+        projectRootDir: options.rootDir,
+      });
+    } catch {
+      // Graceful fallback - no skill selection
+    }
+  }
+
   // Spawn a reviewer agent with read-only tools
   const { session } = await createKbAgent({
     cwd,
@@ -297,6 +315,8 @@ export async function reviewStep(
     fallbackProvider: validatorFallbackProvider,
     fallbackModelId: validatorFallbackModelId,
     defaultThinkingLevel: options.defaultThinkingLevel,
+    // Skill selection: use assigned agent skills if available, otherwise role fallback
+    ...(skillContext?.skillSelectionContext ? { skillSelection: skillContext.skillSelectionContext } : {}),
   });
 
   reviewerLog.log(`${taskId}: reviewer using model ${describeModel(session)}`);

packages/engine/src/triage.ts

@@ -1203,6 +1203,7 @@ export class TriageProcessor {
               defaultThinkingLevel: currentSettings.defaultThinkingLevel,
               store,
               taskId,
+              task: currentDetail,
               userComments: currentUserComments.length > 0 ? currentUserComments : undefined,
               agentStore: this.options.agentStore,
               rootDir,