docs(fleet): north star + Phase-2 observability PRD/tasks (W-FLEET)

Establish Fleet workstream doctrine under mvp-20260312: north star (incl.
fleet-as-means-of-production), Phase-2 observability PRD, workstream tasks,
and scratchpad. Collision-safe: scoped to docs/fleet/, touches none of the
MVP single-writer control-plane files.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RMoEx7hfdFGjUiCHuN1RRi

docs/scratchpads/fleet-observability-phase2.md

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+# 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).
+
+## 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`).