# Sticky implementer session (SDD token optimization)

Reuse the **same implementer subagent** across multiple tasks in one plan when tasks are tightly coupled, same `Execute as` role, and same `Working branch`. **L2 task reviewers stay fresh per task** — do not sticky reviewers.

SSOT for mode selection and host resume → this file (the main skill's dsh continuation-resume clause defers to § Host mapping here). Per-task artifacts → **`file-handoffs.md`**.

**Parallel ready tasks use fresh sessions and task-specific artifact paths inside one canonical per-plan SDD root** (`mstar-sdd` § Ready-task scheduling). Never resume the same session concurrently or share its ledger between tracks; PM alone updates shared context/progress; parallel leaves consume immutable absolute artifact paths, not shared-context helpers.

## When to use

| `SDD implementer session` | Use |
|---------------------------|-----|
| **`fresh`** (default) | Independent tasks, module boundaries, different dev tracks, or first task on a plan |
| **`sticky`** | One sequential dependency chain on one owner track; same `fullstack-dev` (or same role id), sequential tasks on one branch, strong file/context continuity (e.g. T3+T4 daemon stderr + DB reset) |

**Prefer `sticky`** only within a sequential dependency chain with strong context continuity; independent ready tasks remain fresh and concurrent.

## Assignment fields (implement dispatch)

```markdown
**Execution mode**: sdd
**SDD implementer session**: sticky | fresh
**SDD dir**: `{HARNESS_DIR}/sdd/<plan-id>/`
**Execute as**: fullstack-dev
**Working branch**: <branch>
**Covers task**: N | N–M   # single task id for this dispatch turn
```

- **Task 1** (or first task after `fresh` reset): `SDD implementer session: fresh` or `sticky` (starts sticky ledger).
- **Task 2+** with sticky: `SDD implementer session: sticky` + the host's own resume route (§ Host mapping) or the continuation prompt (fallback).

## Session ledger: `implementer-session.json`

PM writes/updates at `{SDD_DIR}/implementer-session.json` when starting or continuing sticky mode:

```json
{
  "plan_id": "<plan-id>",
  "execute_as": "fullstack-dev",
  "session_mode": "sticky",
  "host": "cursor",
  "host_agent_id": "<agent-id from first Task return — required for resume>",
  "working_branch": "feature/...",
  "started_task": 1,
  "last_task": 1,
  "started_at": "2026-07-07T00:00:00Z"
}
```

`host` names the host the ledger belongs to, and `host_agent_id` is the same field on every host: what a resume addresses. On **dsh** that is the durable teammate's `target` in Agent Teams mode, or the continuable `subagent` id on a direct-only profile (no resume token exists there — the id is the resume handle).

After each completed task review, PM sets `last_task` to N. **Do not** resume if `host_agent_id` is missing — fall back to `fresh` for that task.

## Per-task loop (sticky implementer)

Same as default SDD for artifacts and L2 review; only implementer dispatch differs:

1. `mstar sdd task-brief` → `{SDD_DIR}/task-N-brief.md`
2. Record `BASE_SHA`
3. **Implementer dispatch**
   - **First task** (`fresh` or sticky start): normal Task/subagent invoke → save `host_agent_id` to ledger
   - **Next tasks** (`sticky`): host **resume** with same `host_agent_id` + continuation prompt (`implementer-prompt.md` § Continuation)
4. On `DONE` → `mstar sdd review-package` → **fresh** task reviewer (never resume reviewer)
5. Append `progress.md`; update ledger `last_task`
6. Next task

**Still required per task:** commit, `task-N-report.md`, task-level diff, task reviewer, `progress.md` line.
Each task's commit uses the already-configured identity; missing/failing identity is Blocked, never fabricate or use per-commit identity overrides → `mstar-roles/references/_shared/leaf-executor-core.md` § Git NEVER (repo writes).

## When to reset to `fresh`

Start a **new** implementer session (`session_mode: fresh` or new ledger) when any:

- `BLOCKED` / `NEEDS_CONTEXT` not resolved in one continuation turn
- `Execute as` role changes (`fullstack-dev` → `fullstack-dev-2`)
- `Working branch` changes
- Host does not support resume (OpenCode without resume → use **micro-batch** or `fresh`)
- Context clearly degraded (implementer confuses prior tasks) — PM judgment
- Switching from another dev track mid-plan

Delete or archive `implementer-session.json` when resetting.

## Micro-batch fallback (no host resume)

When resume is unavailable, PM may dispatch **one** implementer for **2–3** tightly coupled tasks:

- Prompt lists `task-N-brief.md` … `task-M-brief.md` and matching report paths only
- Implementer completes tasks **in order** in one session
- PM still runs **per-task** `review-package` + **fresh** task reviewer after each task (or after batch if PM documents per-task SHAs in Assignment)

Max **3** tasks per micro-batch without user override. See `project-manager.md` batch sizing.

## Host mapping

| Host | Sticky implementer |
|------|-------------------|
| **Cursor** | `Task` with `resume: <host_agent_id>` — **`mstar-host/references/cursor.md`** § SDD sticky |
| **OpenCode** | Resume only if task tool supports it; else micro-batch or `fresh` per task |
| **Codex** | Thread resume only when callable multi-agent tool documents agent id; else micro-batch or `fresh` |
| **dsh** | **Agent Teams mode (default):** the durable teammate is resumed by name — `send_message` with its `target` — so the teammate, not a resume token, carries the context. **Direct-`subagent` mode:** continuation resume through the recorded continuable id (`send_message`, which takes `agent_id` there). Either way a second child is never spawned for the same work — **`mstar-host/references/dsh.md`** § Pick the delegation channel before you delegate + § Delegation channels |

## PM NEVER (sticky)

- Resume task **reviewer** sessions — reviewers stay fresh per task
- Parallel sticky implementers on the same branch
- Resume without updating `implementer-session.json` / `progress.md`
- Skip per-task review because implementer "remembers" prior tasks
- Paste full plan into continuation prompt — only new brief path + report path