feat(FN-1022): add project memory bootstrap with agent integration

- Add project-memory module in @fusion/core with read/write/resolve helpers and upsert-on-store hook
- Bootstrap project memory during task creation (store) with structured task context
- Inject resolved project memory into executor and triage agent system prompts
- Add comprehensive tests for project-memory module, store integration, and agent prompt changes
- Document project memory architecture and usage in README

packages/engine/src/executor.test.ts

@@ -2163,27 +2163,48 @@ describe("buildExecutionPrompt", () => {
   });
 
   describe("memoryEnabled setting", () => {
-    it("accepts memoryEnabled: true without error", () => {
+    it("includes memory instructions when memoryEnabled: true", () => {
       const task = createMockTaskDetail();
       const result = buildExecutionPrompt(task, "/project", {
         memoryEnabled: true,
       } as any);
-      // Memory instructions are a placeholder until FN-810; just verify no crash
       expect(result).toContain("Execute this task.");
+      expect(result).toContain("## Project Memory");
+      expect(result).toContain(".fusion/memory.md");
     });
 
-    it("accepts memoryEnabled: false without error", () => {
+    it("excludes memory instructions when memoryEnabled: false", () => {
       const task = createMockTaskDetail();
       const result = buildExecutionPrompt(task, "/project", {
         memoryEnabled: false,
       } as any);
       expect(result).toContain("Execute this task.");
+      expect(result).not.toContain("## Project Memory");
     });
 
-    it("accepts undefined memoryEnabled (default enabled) without error", () => {
+    it("includes memory instructions when memoryEnabled is undefined (default enabled)", () => {
       const task = createMockTaskDetail();
       const result = buildExecutionPrompt(task, "/project", {} as any);
       expect(result).toContain("Execute this task.");
+      expect(result).toContain("## Project Memory");
+      expect(result).toContain(".fusion/memory.md");
+    });
+
+    it("includes append instruction for updating memory at end of execution", () => {
+      const task = createMockTaskDetail();
+      const result = buildExecutionPrompt(task, "/project", {
+        memoryEnabled: true,
+      } as any);
+      expect(result).toContain("append");
+      expect(result).toMatch(/end of execution|before calling.*task_done/i);
+    });
+
+    it("uses project-root memory path not worktree-local path", () => {
+      const task = createMockTaskDetail();
+      const result = buildExecutionPrompt(task, "/project", {
+        memoryEnabled: true,
+      } as any);
+      expect(result).toContain("`.fusion/memory.md`");
     });
   });
 });

packages/engine/src/executor.ts

@@ -3,6 +3,7 @@ import { join } from "node:path";
 import { existsSync } from "node:fs";
 import type { TaskStore, Task, TaskDetail, StepStatus, Settings, WorkflowStep, MissionStore, Slice, AgentState, AgentCapability } from "@fusion/core";
 import type { AgentStore } from "@fusion/core";
+import { buildExecutionMemoryInstructions } from "@fusion/core";
 import { findWorktreeUser } from "./merger.js";
 import { generateWorktreeName, slugify } from "./worktree-names.js";
 import { Type, type Static } from "@mariozechner/pi-ai";
@@ -3024,13 +3025,10 @@ git log --oneline
 
   // Build project memory section from settings
   // When enabled, agents consult and update .fusion/memory.md for durable project learnings.
-  // Actual memory instructions will be injected by FN-810; this placeholder establishes
-  // the conditional integration point.
   const memoryEnabled = settings?.memoryEnabled !== false;
   let memorySection = "";
   if (memoryEnabled && rootDir) {
-    // TODO(FN-810): Call buildMemoryInstructions(rootDir) to populate memory context
-    memorySection = "";
+    memorySection = "\n" + buildExecutionMemoryInstructions(rootDir);
   }
 
   // Build steering comments section (last 10 comments only to avoid context bloat)

packages/engine/src/triage.test.ts

@@ -217,7 +217,7 @@ describe("buildSpecificationPrompt", () => {
   });
 
   describe("memoryEnabled setting", () => {
-    it("accepts memoryEnabled: true without error", () => {
+    it("includes memory instructions when memoryEnabled: true", () => {
       const settings: Settings = {
         maxConcurrent: 2,
         maxWorktrees: 4,
@@ -231,11 +231,12 @@ describe("buildSpecificationPrompt", () => {
         ".fusion/tasks/KB-001/PROMPT.md",
         settings,
       );
-      // Memory instructions are a placeholder until FN-810; just verify no crash
       expect(prompt).toContain("Specify this task");
+      expect(prompt).toContain("## Project Memory");
+      expect(prompt).toContain(".fusion/memory.md");
     });
 
-    it("accepts memoryEnabled: false without error", () => {
+    it("excludes memory instructions when memoryEnabled: false", () => {
       const settings: Settings = {
         maxConcurrent: 2,
         maxWorktrees: 4,
@@ -250,15 +251,18 @@ describe("buildSpecificationPrompt", () => {
         settings,
       );
       expect(prompt).toContain("Specify this task");
+      expect(prompt).not.toContain("## Project Memory");
     });
 
-    it("accepts undefined memoryEnabled (default enabled) without error", () => {
+    it("includes memory instructions when memoryEnabled is undefined (default enabled)", () => {
       const prompt = buildSpecificationPrompt(
         baseTask,
         ".fusion/tasks/KB-001/PROMPT.md",
         undefined,
       );
       expect(prompt).toContain("Specify this task");
+      expect(prompt).toContain("## Project Memory");
+      expect(prompt).toContain(".fusion/memory.md");
     });
   });
 

packages/engine/src/triage.ts

@@ -5,6 +5,7 @@ import type {
   TaskAttachment,
   Settings,
 } from "@fusion/core";
+import { buildTriageMemoryInstructions } from "@fusion/core";
 import type { ImageContent } from "@mariozechner/pi-ai";
 import { Type, type Static } from "@mariozechner/pi-ai";
 import type {
@@ -1252,13 +1253,10 @@ export function buildSpecificationPrompt(
 
   // Build project memory section from settings.
   // When enabled, agents consult .fusion/memory.md for durable project learnings.
-  // Actual memory instructions will be injected by FN-810; this placeholder
-  // establishes the conditional integration point.
   const memoryEnabled = settings?.memoryEnabled !== false;
   let memorySection = "";
   if (memoryEnabled) {
-    // TODO(FN-810): Call buildMemoryInstructions(rootDir) to populate memory context
-    memorySection = "";
+    memorySection = "\n\n" + buildTriageMemoryInstructions("");
   }
 
   let attachmentsSection = "";