Add session-aware task context and auto-linking (CF-166 Phase 2)

Enhancements:

1. Session Context Table
   - Migration 014: session_context table
   - Tracks current working task per session
   - Auto-updated on task status changes

2. Auto-Linking to Current Working Task
   - When task status → in_progress: sets as current_task_id
   - When task status → completed: clears current_task_id
   - New tasks auto-link to current working task with 'relates_to'
   - Shows auto-link message during task creation

3. Session ID Resolution
   - Fixed path: ~/.cache/session-memory/current_session
   - Falls back to environment variable CLAUDE_SESSION_ID
   - Generates timestamp-based ID if unavailable

Example Flow:
```
1. task update CF-123 --status in_progress
   → Sets CF-123 as current working task

2. task add --title "Related work"
   → Created: CF-124
   🔗 Auto-linked to: CF-123 (current working task)

3. task update CF-123 --status completed
   → Clears current working task
```

Files Changed:
- migrations/014_session_context.sql (new, 33 lines)
- src/tools/crud.ts (auto-linking logic, session context management)

Benefits:
- Zero manual linking for related work
- Session context preserved automatically
- Investigation workflows auto-organized
- Retroactive work tracking prevented

Note: Requires MCP server restart to take effect.

Remaining CF-166 Features (Phase 3):
- task investigate command
- Investigation workflow helper
- Task creation reminders

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

migrations/014_session_context.sql

@@ -0,0 +1,28 @@
+-- Migration 014: Session Context for Auto-linking
+-- Tracks current working task per session for automatic task relationship creation
+
+CREATE TABLE IF NOT EXISTS session_context (
+    session_id TEXT PRIMARY KEY,
+    current_task_id TEXT REFERENCES tasks(id) ON DELETE SET NULL,
+    updated_at TIMESTAMP WITH TIME ZONE DEFAULT NOW()
+);
+
+CREATE INDEX IF NOT EXISTS idx_session_context_task ON session_context(current_task_id);
+
+-- Auto-update timestamp on changes
+CREATE OR REPLACE FUNCTION update_session_context_timestamp()
+RETURNS TRIGGER AS $$
+BEGIN
+    NEW.updated_at = NOW();
+    RETURN NEW;
+END;
+$$ LANGUAGE plpgsql;
+
+CREATE TRIGGER session_context_updated
+    BEFORE UPDATE ON session_context
+    FOR EACH ROW
+    EXECUTE FUNCTION update_session_context_timestamp();
+
+-- Record migration
+INSERT INTO schema_migrations (version) VALUES ('014_session_context')
+ON CONFLICT (version) DO NOTHING;

src/tools/crud.ts

@@ -5,6 +5,7 @@ import { getEmbedding, formatEmbedding } from '../embeddings.js';
 import type { Task, ChecklistItem, TaskLink } from '../types.js';
 import { getRecentDelegations } from './delegations.js';
 import { getTaskCommits } from './commits.js';
+import { taskLink } from './relations.js';
 import * as fs from 'fs';
 import * as path from 'path';
 import * as os from 'os';
@@ -18,8 +19,8 @@ function getSessionId(): string {
     return process.env.CLAUDE_SESSION_ID;
   }
 
-  // Try to read from cache file (usage-stats format)
-  const cacheFile = path.join(os.homedir(), '.claude', 'cache', '.current_session_id');
+  // Try to read from cache file (session-memory format)
+  const cacheFile = path.join(os.homedir(), '.cache', 'session-memory', 'current_session');
   try {
     const sessionId = fs.readFileSync(cacheFile, 'utf-8').trim();
     if (sessionId) return sessionId;
@@ -138,7 +139,29 @@ export async function taskAdd(args: TaskAddArgs): Promise<string> {
   // Record activity for session tracking
   await recordActivity(taskId, 'created', undefined, 'open');
 
-  return `Created: ${taskId}\n  Title: ${title}\n  Type: ${type}\n  Priority: ${priority}\n  Project: ${projectKey}${embedding ? '\n  (embedded for semantic search)' : ''}${duplicateWarning}`;
+  // Check for session context and auto-link to current working task
+  let autoLinkMessage = '';
+  const session_id = getSessionId();
+  try {
+    const sessionContext = await queryOne<{ current_task_id: string }>(
+      `SELECT current_task_id FROM session_context WHERE session_id = $1`,
+      [session_id]
+    );
+
+    if (sessionContext?.current_task_id) {
+      // Auto-link to current working task
+      await taskLink({
+        from_id: taskId,
+        to_id: sessionContext.current_task_id,
+        link_type: 'relates_to'
+      });
+      autoLinkMessage = `\n\n🔗 Auto-linked to: ${sessionContext.current_task_id} (current working task)`;
+    }
+  } catch {
+    // Silently fail if session context unavailable
+  }
+
+  return `Created: ${taskId}\n  Title: ${title}\n  Type: ${type}\n  Priority: ${priority}\n  Project: ${projectKey}${embedding ? '\n  (embedded for semantic search)' : ''}${duplicateWarning}${autoLinkMessage}`;
 }
 
 /**
@@ -404,5 +427,30 @@ export async function taskUpdate(args: TaskUpdateArgs): Promise<string> {
     await recordActivity(id, 'updated');
   }
 
+  // Manage session context based on status changes
+  if (status) {
+    const session_id = getSessionId();
+    try {
+      if (status === 'in_progress') {
+        // Set as current working task
+        await execute(
+          `INSERT INTO session_context (session_id, current_task_id)
+           VALUES ($1, $2)
+           ON CONFLICT (session_id) DO UPDATE SET current_task_id = $2, updated_at = NOW()`,
+          [session_id, id]
+        );
+      } else if (status === 'completed') {
+        // Clear if this is the current working task
+        await execute(
+          `DELETE FROM session_context
+           WHERE session_id = $1 AND current_task_id = $2`,
+          [session_id, id]
+        );
+      }
+    } catch {
+      // Silently fail if session context unavailable
+    }
+  }
+
   return `Updated: ${id}`;
 }