fix(FN-2078): adopt canonical .fusion/memory paths

- Update core and engine prompt text to reference .fusion/memory/ with MEMORY.md and daily-note guidance
- Allow worktree tool boundary access to .fusion/memory/ files while preserving legacy .fusion/memory.md compatibility
- Revise memory compaction/insight extraction messaging and related type/docs comments to use canonical memory paths
- Refresh dashboard and test expectations across core/engine/dashboard/docs for the new memory path wording

packages/engine/src/pi.ts

@@ -559,7 +559,7 @@ async function assertValidWorktreeSession(cwd: string, projectRoot: string): Pro
  * Check if a path is allowed to be accessed from a worktree session.
  * Rules:
  * - Paths inside the worktree are always allowed
- * - Project root .fusion/memory.md is allowed (for durable project learnings)
+ * - Project root .fusion/memory/ directory is allowed (MEMORY.md, YYYY-MM-DD.md, DREAMS.md)
  * - Task attachments under .fusion/tasks/N/attachments/ are allowed (for reading context files)
  * - All other paths outside the worktree are rejected
  *
@@ -580,9 +580,9 @@ function isWorktreeAllowedPath(worktreePath: string, projectRoot: string, reques
     return true; // Path is inside the worktree
   }
 
-  // Exception: project root `.fusion/memory.md` for durable project learnings
+  // Exception: project root `.fusion/memory/` directory for durable project learnings
   const relToProjectRoot = relative(projectRootResolved, requestedResolved);
-  if (relToProjectRoot === ".fusion/memory.md") {
+  if (relToProjectRoot === ".fusion/memory.md" || relToProjectRoot.startsWith(".fusion/memory/")) {
     return true;
   }
 
@@ -640,7 +640,7 @@ export function wrapToolsWithBoundary(
             ok: false,
             error: `Path "${relToProject}" is outside the worktree boundary. ` +
               `Coding agents can only modify files inside the current worktree. ` +
-              `Exception: .fusion/memory.md (project root) and .fusion/tasks/*/attachments/* are permitted for reading.`,
+              `Exception: .fusion/memory/ directory (project root) and .fusion/tasks/*/attachments/* are permitted for reading.`,
           };
         }