feat(fleet): Phase-2 observability — fleet ps + watch + send verify (#579)

docs/scratchpads/fleet-observability-phase2.md

@@ -0,0 +1,75 @@
+# Scratchpad — Fleet Phase 2: Observability (W-FLEET)
+
+> Append-only. Mission `mvp-20260312` / workstream W-FLEET.
+> Lead: Jarvis (Claude) at `W-jarvis:mos-claude-18`. Coordinating with `jwoltje@dragon-lin:coder0-0`.
+
+## Mission prompt (2026-06-20)
+
+Establish the north star for the Mosaic Fleet feature and prepare Phase-2 observability
+for delivery. The USC tmux PoC is the proven base. Jason granted lead authority:
+"The fleet is a great way to actually build the MVP — we are building the system that
+builds the system." Dogfood actual agent construction + ad-hoc deployment; coordinate
+with a second agent on `dragon-lin`.
+
+## Decisions of record (with Jason, 2026-06-20)
+
+- Agent model: config defines, session runs (gateway = definition/identity/auth; tmux = runtime).
+- Tenancy: multi-tenant from the start; isolation = per-tenant Linux uid.
+- Health: heartbeat required; dogfood stub implements protocol now.
+- Lifecycle: hybrid (core always-on + ephemeral workers).
+- Observation: read-only default, opt-in takeover.
+- Multi-host: designed-for day one; control plane rides federation (W1), not a bespoke broker.
+- Delivery: CLI-first, dogfood on the live stub fleet; webUI deferred to Phase 5.
+- Fleet is dual-role: product AND means of production (bootstrapping the MVP).
+- Code review = **dual-engine**: Claude **and** gpt-5.5/Codex, run together (Jason: the
+  combination produces the best results). Launch reviewers via `mosaic yolo pi` / `codex`
+  (proven path) or `~/.config/mosaic/tools/codex/codex-code-review.sh`. Applies to all
+  code-review gates incl. FLEET-OBS-008. Per Jason 2026-06-20.
+- Worktree discipline: do fleet work in `~/src/mosaicstack-stack-worktrees/<branch>`, NOT
+  the shared main checkout — concurrent processes mutate `main` there (learned 2026-06-20).
+
+## Environment facts (verified 2026-06-20)
+
+- Fleet is live on `W-jarvis` (uid 1000, `jarvis`, `Linger=yes`) on tmux socket
+  `mosaic-factory`: `_holder`, `canary-pi`, `dogfood-coder`, `dogfood-orchestrator`,
+  `dogfood-reviewer`. All panes run `~/.config/mosaic/fleet/dogfood-agent.py` (stub),
+  including `canary-pi` (roster says runtime=pi → **drift**).
+- Holder + `mosaic-agent@*` units are `active (exited)` but `UnitFileState=disabled`
+  (reboot loses fleet → boot-enable gap to surface).
+- Observation blocked by: isolated socket (hidden from default `tmux ls`), `capture-pane`
+  blank for TUIs, `attach` being read-write + resizing.
+- Second agent: `jwoltje@dragon-lin`, session `coder0-0` (group `coder0`), running `node`,
+  default socket. ssh forward reach confirmed.
+
+## Governance / collision-safety
+
+- `mosaicstack-stack` has active mission `mvp-20260312` with single-writer locks on
+  `docs/MISSION-MANIFEST.md`, `docs/TASKS.md`, `docs/scratchpads/mvp-20260312.md`.
+- This workstream touches NONE of those. All Fleet docs scoped under `docs/fleet/` +
+  this scratchpad. Rollup row proposed, not written.
+
+## Session log
+
+- 2026-06-20: Researched AI guide + fleet code + live state. Established north star with
+  Jason (8 forks decided). Branched `feat/fleet-observability`. Persisted
+  `docs/fleet/{north-star.md,PRD.md,TASKS.md}` + this scratchpad. Next: establish comms
+  with dragon-lin coder, commit docs, begin Phase-2 delivery (heartbeat + `fleet ps`).
+- 2026-06-20 (session 2): Built Phase-2 CLI via worker (commit ab47831): `fleet ps`,
+  `agent watch`, `agent send --verify`, 62 tests. LIVE-verified `fleet ps` on
+  mosaic-factory — correctly flagged canary-pi DRIFT + BOOT-ENABLE, tenant_id+host in JSON.
+  Heartbeat responder added to dogfood-agent.py (FLEET-OBS-002) — `fleet ps` HB now
+  `healthy` for all 4 agents.
+- Coordination: dual-engine-reviewed (Claude+Codex) and merged framework PRs #572
+  (sanitization gate) + #575 (CONSTITUTION extraction) as Lead. Codex caught an Alpine
+  blocker on #572 (refuted by CI); Claude caught a CI-breaking format failure on #575.
+- **FINDINGS (north-star / Phase-3 blockers):**
+  1. Ad-hoc `mosaic yolo {codex,pi}` via `start-agent-session.sh` DIE immediately in a
+     detached tmux pane (codex: "stdin is not a terminal"; pi: same). Only the python stub
+     survives. => Real runtimes have NEVER run durably in the fleet. Launch path (PATH/TTY
+     in the detached shell) must be fixed before Phase-3 real-runtime swap. `fleet ps`
+     caught both dead panes instantly (tool validated).
+  2. `MOSAIC_AGENT_NAME` (set in systemd EnvironmentFile) is NOT propagated into tmux's
+     global env, so agents defaulted to `unknown`. Worked around in dogfood-agent.py via
+     tmux session-name fallback; the systemd/tmux env handoff needs a real fix.
+- Next: rebase on merged main, open Phase-2 PR, dual-engine review, merge, close
+  `fleet-observability-1`. Defer launch-path + env-propagation fixes to Phase 3.