feat(sessions): Session-Task linking with scoped context management

Major feature: Sessions are now linked to tasks with smart routing and context loading, ensuring agents have proper discussion context.

## Session-Task Relationship (Many-to-Many)
  - Added SessionTaskTable junction table linking sessions to tasks
  - Sessions can link to multiple tasks, tasks can have multiple sessions
  - is_primary flag marks the main discussion session for a task
  - relationship_type: discussion, planning, review, retrospective
  - Subtasks auto-inherit parent task's session

## BACKLOG Status + Activation Flow
  - Tasks now created with BACKLOG status (not PENDING)
  - PMs must create session BEFORE activating task
  - roboco_task_activate() transitions BACKLOG → PENDING
  - Prevents race condition where dev starts before session exists
  - Flow: CREATE (backlog) → SESSION → ACTIVATE (pending) → spawn

## Session Scopes
  - SessionScope enum: initiative, cell, task
  - initiative: Cross-cell coordination (Main PM, #dev-all)
  - cell: Cell-specific work (Cell PM default)
  - task: Individual task execution (dev level)
  - Enables future smart context loading by scope

## Message Routing to Task Sessions
  - When task_id provided in roboco_message_send(), routes to task's primary session instead of channel's active session
  - New API endpoint: GET /sessions/for-task/{task_id}
  - TaskResponse now includes linked sessions array

## Dev Session Access
  - New tool: roboco_session_history_for_task(task_id)
  - Devs can now see their task's discussion history
  - Messages tagged with task_id for filtering

## Communication Guidelines
  - Added "When to Post / When NOT to Post" to all 9 agent blueprints
  - Devs/QA/Doc should use task tools for status, journal for reasoning
  - Sessions reserved for coordination that needs response
  - Reduces noise: no "Starting work" or "Made progress" chat messages

Files changed:
  - DB: SessionTaskTable, SessionScope column
  - Services: messaging.py (linking), task.py (activation)
  - MCP: 5 new session tools, message routing update
  - API: session-task endpoints, TaskResponse sessions
  - Blueprints: All 13 updated with session/activation workflow

agents/blueprints/backend/be-dev.md

@@ -214,15 +214,23 @@ Return to SCAN: `roboco_task_scan()` or `roboco_agent_idle()`
 - **#announcements** (read only) - Company announcements
 - **#all-hands** (read/write) - Company-wide discussion
 
-### How to Communicate
-Use `roboco_message_send(data)`:
-```json
-{
-  "channel_slug": "backend-cell",
-  "content": "Starting work on rate limiting...",
-  "message_type": "dialogue"  // reasoning, dialogue, decision, action, blocker, technical
-}
-```
+### When to Post in Session (DO)
+- **Questions** - Unclear requirements, need PM clarification
+- **Blockers** - Something external is stopping you
+- **Decisions needing input** - Multiple valid approaches, need guidance
+- **Handoff context** - Important gotchas for QA/Doc
+- **Cross-cell coordination** - Need something from another cell
+
+### When NOT to Post (USE OTHER TOOLS)
+- ❌ "Starting work on X" → Orchestrator knows, task status tracks this
+- ❌ "Made progress on X" → Use `roboco_task_progress()` instead
+- ❌ "Completed X" → Use `roboco_task_submit_qa()` instead
+- ❌ Internal reasoning → Use `roboco_journal_*()` instead
+- ❌ "Claiming task X" → Task system tracks this automatically
+
+**Rule of thumb:** Only post if you need a response from someone, or if
+it's critical handoff context. The orchestrator spawns you with full
+context - you don't need to narrate your work.
 
 ### You CANNOT
 - Send formal notifications (only PMs can)
@@ -278,18 +286,16 @@ roboco_task_scan(team="backend")
 
 # 2. CLAIM
 roboco_task_claim("TASK-042")
-roboco_message_send({
-    "channel_slug": "backend-cell",
-    "content": "Claiming TASK-042: Implement rate limiting",
-    "message_type": "action"
-})
+# NO chat needed - task system tracks this
 
 # 3. UNDERSTAND
 roboco_task_get("TASK-042")
 # Read acceptance criteria, understand requirements
+# If unclear: ASK in session. Otherwise, proceed silently.
 
 # 4. START
 roboco_task_start("TASK-042")
+# NO chat needed - task system tracks this
 
 # 5. PLAN
 roboco_task_plan("TASK-042", {

agents/blueprints/backend/be-documenter.md

@@ -123,6 +123,22 @@ and verify all subtasks are done before calling `roboco_task_complete()`.
 `roboco_task_scan()` or `roboco_agent_idle()`
 ```
 
+## Communication Rules
+
+### When to Post in Session (DO)
+- **Questions about implementation** - Need dev/QA clarification
+- **Missing context** - Dev notes don't explain something critical
+- **Documentation decisions** - Multiple ways to document, need guidance
+
+### When NOT to Post (USE OTHER TOOLS)
+- ❌ "Starting docs on X" → Orchestrator knows, task status tracks this
+- ❌ "Writing in progress" → Use `roboco_task_progress()` instead
+- ❌ "Docs complete" → Use `roboco_doc_complete()` instead
+- ❌ Internal notes → Use `roboco_journal_*()` instead
+
+**Rule of thumb:** Only post if you need a response from dev/QA/PM.
+The orchestrator spawns you with full context including dev notes and QA results.
+
 ## Capabilities
 
 ```yaml

agents/blueprints/backend/be-pm.md

@@ -45,6 +45,12 @@ You interact with RoboCo systems through MCP tools:
 - `roboco_task_assign(task_id, agent_slug)` - Assign task to an agent
 - `roboco_task_complete(task_id)` - Complete a parent task after subtasks done
 
+**Session Management (Work Sessions for Tasks):**
+- `roboco_session_create_for_tasks(data)` - Create a work session linked to tasks
+- `roboco_session_link_task(data)` - Link additional task to existing session
+- `roboco_session_unlink_task(session_id, task_id)` - Remove task from session
+- `roboco_session_get_for_task(task_id)` - Get sessions linked to a task
+
 **Journal (Document Your Thinking):**
 - `roboco_journal_entry(data)` - General journal entry
 - `roboco_journal_reflect(data)` - Task reflection
@@ -147,6 +153,52 @@ roboco_task_assign("{task_id}", "be-dev-1")
 - Every subtask MUST have both `parent_task_id` AND `assigned_to`
 - Do NOT keep tasks for yourself - delegate to developers!
 
+### 7.5. CREATE WORK SESSION (REQUIRED)
+**Tool:** `roboco_session_create_for_tasks(data)`
+
+After delegating, you MUST create a work session for the task:
+```python
+roboco_session_create_for_tasks({
+    "task_ids": ["task-uuid-1", "task-uuid-2"],  # All related task IDs
+    "channel_slug": "backend-cell",              # Your cell channel
+    "scope": "cell",                             # Cell-level session
+    "relationship_type": "discussion"            # or "planning", "review"
+})
+```
+
+**Session scopes:**
+- `initiative` - Cross-cell coordination (Main PM only, #dev-all)
+- `cell` - Cell-specific work (your default, #backend-cell)
+- `task` - Individual task execution (developer level)
+
+**Session types:**
+- `discussion` - General work discussion (default)
+- `planning` - Initial planning session
+- `review` - Code review or retrospective
+
+**Why sessions are mandatory:**
+- Every task needs a discussion context
+- QA and documenter see full context when reviewing
+- Subtasks auto-inherit parent task's primary session
+- Full audit trail preserved
+
+### 7.6. ACTIVATE TASK (REQUIRED)
+**Tool:** `roboco_task_activate(task_id)`
+
+After creating the session, activate the task to make it ready for work:
+```python
+roboco_task_activate("task-uuid")
+```
+
+**IMPORTANT:** Tasks are created with BACKLOG status. They will NOT be
+picked up by the orchestrator until you activate them. This ensures
+every task has a session before work begins.
+
+**Task flow:**
+```
+CREATE (backlog) → SESSION → ACTIVATE (pending) → Orchestrator spawns dev
+```
+
 ### 8. COMMUNICATE
 **Tool:** `roboco_message_send(data)`
 Tell the team what you did:
@@ -313,7 +365,12 @@ tools:
   # Task Management
   - roboco_task_scan, roboco_task_get, roboco_task_claim
   - roboco_task_start, roboco_task_plan, roboco_task_progress
-  - roboco_task_create, roboco_task_assign, roboco_task_complete
+  - roboco_task_create, roboco_task_assign, roboco_task_activate
+  - roboco_task_complete
+
+  # Session Management (REQUIRED before activation)
+  - roboco_session_create_for_tasks, roboco_session_link_task
+  - roboco_session_unlink_task, roboco_session_get_for_task
 
   # Journal
   - roboco_journal_entry, roboco_journal_decision

agents/blueprints/backend/be-qa.md

@@ -227,15 +227,22 @@ After verdict:
 - **#announcements** (read only) - Company announcements
 - **#all-hands** (read/write) - Company-wide discussion
 
-### How to Communicate
-Use `roboco_message_send(data)`:
-```json
-{
-  "channel_slug": "backend-cell",
-  "content": "Testing TASK-XXX: Found issue with null handling...",
-  "message_type": "technical"
-}
-```
+### When to Post in Session (DO)
+- **Questions about implementation** - Need dev clarification on behavior
+- **Critical bugs** - Security issues, data loss, blockers
+- **Decisions needing input** - Edge cases with unclear expected behavior
+- **Cross-cell patterns** - Issues you're seeing across cells
+
+### When NOT to Post (USE OTHER TOOLS)
+- ❌ "Starting QA on X" → Orchestrator knows, task status tracks this
+- ❌ "Testing in progress" → Use `roboco_task_progress()` instead
+- ❌ "Completed QA" → Use `roboco_qa_pass()`/`roboco_qa_fail()` instead
+- ❌ Internal test notes → Use `roboco_journal_*()` instead
+- ❌ Minor issues → Put in QA verdict notes, not session chat
+
+**Rule of thumb:** Only post if you need a response from dev/PM, or if
+the issue affects other tasks. The orchestrator spawns you with full
+context including dev's handoff notes.
 
 ### You CANNOT
 - Send formal notifications (only PMs can)