chore(workflow): sync backlog state and subagent coordination

Capture backlog task lifecycle updates, archive TASK-34, and add planning artifacts for recent config work. Update docs sweep scripts and AGENTS guidance to use sharded docs/subagents coordination metadata.

AGENTS.md

@@ -27,3 +27,46 @@ You MUST read the overview resource to understand the complete workflow. The inf
 </CRITICAL_INSTRUCTION>
 
 <!-- BACKLOG.MD MCP GUIDELINES END -->
+
+## Subagent Coordination Protocol (`docs/subagents/`)
+
+Purpose: multi-agent coordination across runs; single-agent continuity during long runs.
+
+Layout:
+- `docs/subagents/INDEX.md` (active agents table)
+- `docs/subagents/collaboration.md` (shared notes)
+- `docs/subagents/agents/<agent_id>.md` (one file per agent)
+- `docs/subagents/archive/<yyyy-mm>/` (archived histories)
+
+Required behavior (all agents):
+
+1. At run start, read in order:
+   - `docs/subagents/INDEX.md`
+   - `docs/subagents/collaboration.md`
+   - your own file: `docs/subagents/agents/<agent_id>.md`
+2. Identify self by stable `agent_id` (runner/env-provided). If missing, create own file from template.
+3. Maintain `alias` (short human-readable label) + `mission` (one-line focus).
+4. Before coding:
+   - record intent, planned files, assumptions in your own file.
+5. During run:
+   - update on phase changes (plan -> edit -> test -> handoff),
+   - heartbeat at least every `HEARTBEAT_MINUTES` (default 5),
+   - update your own row in `INDEX.md` (`status`, `last_update_utc`),
+   - append cross-agent notes in `collaboration.md` when needed.
+6. Write limits:
+   - MAY edit own file.
+   - MAY append to `collaboration.md`.
+   - MAY edit only own row in `INDEX.md`.
+   - MUST NOT edit other agent files.
+7. At run end:
+   - record files touched, key decisions, assumptions, blockers, next step for handoff.
+8. Conflict handling:
+   - if another agent touched your target files, add conflict note in `collaboration.md` before continuing.
+9. Brevity:
+   - terse bullets; factual; no long prose.
+
+Suggested env vars:
+
+- `AGENT_ID` (required)
+- `AGENT_ALIAS` (required)
+- `HEARTBEAT_MINUTES` (optional, default 20)