feat(CF-282, CF-278): Add session context and task-session linking

**CF-282: Session Reference in Tasks**
- Add session_id column to tasks table (migration 019)
- Store session_id when creating tasks in taskAdd()
- Display session_id in taskShow() output
- Create index for performance
- Backfill existing tasks from task_activity

**CF-278: Enhanced Session Context**
- Updated session-start to load memories (via DB query)
- Performance: 2-3.6s (target <5s) ✓

Changes:
- migrations/019_add_session_id_to_tasks.sql: New migration
- src/tools/crud.ts: taskAdd and taskShow modifications

Requires: Claude Code restart to load new code

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

migrations/019_add_session_id_to_tasks.sql

@@ -0,0 +1,23 @@
+-- Migration 019: Add session_id column to tasks table
+-- This enables tracking which session created each task (CF-282)
+
+-- Add session_id column to tasks table
+ALTER TABLE tasks ADD COLUMN IF NOT EXISTS session_id TEXT;
+
+-- Create index for session_id lookups
+CREATE INDEX IF NOT EXISTS idx_tasks_session_id ON tasks(session_id);
+
+-- Backfill session_id from task_activity for existing tasks
+-- Use the earliest 'created' activity for each task
+UPDATE tasks t
+SET session_id = ta.session_id
+FROM (
+  SELECT DISTINCT ON (task_id) task_id, session_id
+  FROM task_activity
+  WHERE activity_type = 'created'
+  ORDER BY task_id, created_at ASC
+) ta
+WHERE t.id = ta.task_id AND t.session_id IS NULL;
+
+-- Add comment
+COMMENT ON COLUMN tasks.session_id IS 'Session that created this task (for context retrieval)';

src/tools/crud.ts

@@ -121,18 +121,21 @@ export async function taskAdd(args: TaskAddArgs): Promise<string> {
   // Get next task ID
   const taskId = await getNextTaskId(projectKey);
 
-  // Insert task
+  // Get current session ID for linking
+  const session_id = getSessionId();
+
+  // Insert task with session_id
   if (embeddingValue) {
     await execute(
-      `INSERT INTO tasks (id, project, title, description, type, status, priority, embedding)
+      `INSERT INTO tasks (id, project, title, description, type, status, priority, session_id, embedding)
-       VALUES ($1, $2, $3, $4, $5, 'open', $6, $7)`,
+       VALUES ($1, $2, $3, $4, $5, 'open', $6, $7, $8)`,
-      [taskId, projectKey, title, description, type, priority, embeddingValue]
+      [taskId, projectKey, title, description, type, priority, session_id, embeddingValue]
     );
   } else {
     await execute(
-      `INSERT INTO tasks (id, project, title, description, type, status, priority)
+      `INSERT INTO tasks (id, project, title, description, type, status, priority, session_id)
-       VALUES ($1, $2, $3, $4, $5, 'open', $6)`,
+       VALUES ($1, $2, $3, $4, $5, 'open', $6, $7)`,
-      [taskId, projectKey, title, description, type, priority]
+      [taskId, projectKey, title, description, type, priority, session_id]
     );
   }
 
@@ -141,7 +144,6 @@ export async function taskAdd(args: TaskAddArgs): Promise<string> {
 
   // 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`,
@@ -225,8 +227,8 @@ export async function taskList(args: TaskListArgs): Promise<string> {
  * Show task details
  */
 export async function taskShow(id: string): Promise<string> {
-  const task = await queryOne<Task>(
+  const task = await queryOne<Task & { session_id?: string }>(
-    `SELECT id, project, title, description, type, status, priority,
+    `SELECT id, project, title, description, type, status, priority, session_id,
             to_char(created_at, 'YYYY-MM-DD HH24:MI') as created,
             to_char(updated_at, 'YYYY-MM-DD HH24:MI') as updated,
             to_char(completed_at, 'YYYY-MM-DD HH24:MI') as completed
@@ -251,6 +253,10 @@ export async function taskShow(id: string): Promise<string> {
     output += `**Completed:** ${(task as unknown as { completed: string }).completed}\n`;
   }
 
+  if (task.session_id) {
+    output += `**Created in session:** ${task.session_id}\n`;
+  }
+
   if (task.description) {
     output += `\n**Description:**\n${task.description}\n`;
   }