fix(fleet): report idle agents as available, reserve stuck for genuine blocks (#653)

docs/scratchpads/h2-readiness-available.md

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+# H2 — readiness semantics: available, not stuck
+
+## Objective
+
+Correct fleet readiness semantics so a healthy long-idle agent is reported as `available` (good/assignable) instead of `stuck` (fault). Reserve `stuck` in the type/JSON value space for future positive block evidence.
+
+## Scope
+
+- `packages/mosaic/src/commands/fleet.ts`
+  - replace `idle` readiness state with `available`
+  - keep `stuck` in the union but stop emitting it from idle-only heuristics
+  - remove stuck threshold helper/env handling
+  - remove IDLE/STUCK alarm flags from table rendering
+- `packages/mosaic/src/commands/fleet.spec.ts`
+  - update classifier branch/boundary tests
+  - assert very long idle maps to `available`, not `stuck`
+  - update table/JSON assertions for available with no alarm flags
+  - remove stuck threshold helper tests
+
+## Acceptance Criteria
+
+- `classifyReadiness()` remains pure/total/never-throw and maps:
+  - dead/stale/unknown unchanged
+  - busy/null/undefined/non-finite idle to `working`
+  - idle >= activity threshold to `available`
+  - idle < activity threshold to `working`
+- No idle-derived path emits `stuck`.
+- `MOSAIC_HEARTBEAT_IDLE_THRESHOLD` remains backward compatible as the working→available activity threshold.
+- `MOSAIC_HEARTBEAT_STUCK_THRESHOLD` and helper/default are removed.
+- `fleet ps` keeps the idle-seconds column header `IDLE`, renders `available` in HB label, and does not add IDLE/STUCK warning flags.
+- Local gates green: build precheck, typecheck, lint, format:check, fleet vitest.
+- PR opened against `main`; no merge by worker.
+
+## Constraints / Assumptions
+
+- Source branch: `origin/main` @ `1020cfa`.
+- `docs/TASKS.md` is orchestrator-owned; worker will not modify it.
+- Documentation impact is captured in this scratchpad and PR description; no user/admin guide behavior beyond CLI readiness label semantics.
+
+## Plan
+
+1. Install dependencies with requested PNPM environment.
+2. Inspect current H1/H1b readiness implementation and tests.
+3. Update classifier types/helpers/rendering.
+4. Update focused tests.
+5. Run build precheck + required gates.
+6. Run automated code review, remediate any findings.
+7. Queue guard, push, open PR.
+
+## Progress
+
+- 2026-06-24: Branch created from `origin/main` @ `1020cfa`.
+- 2026-06-24: Replaced idle-derived `idle`/`stuck` outputs with `available`; retained `stuck` in type union for future positive block evidence.
+- 2026-06-24: Removed stuck threshold env/helper plumbing and IDLE/STUCK alarm flags.
+- 2026-06-24: Updated classifier and table-render tests for available semantics.
+
+## Verification Evidence
+
+- `pnpm install --store-dir "$HOME/.pnpm-store"` — pass.
+- `npx turbo build --filter=@mosaicstack/mosaic^...` — pass, 12/12 tasks successful.
+- `pnpm typecheck` — pass, 41/41 tasks successful.
+- `pnpm lint` — pass, 23/23 tasks successful.
+- `pnpm format:check` — pass, all matched files use Prettier style.
+- `pnpm --filter @mosaicstack/mosaic exec vitest run src/commands/fleet.spec.ts` — pass, 177 tests.
+- `~/.config/mosaic/tools/codex/codex-code-review.sh --uncommitted` — approve, 0 findings (reviewed supplied diff; sandbox file-inspection limitation noted by tool).
+
+## Risks / Blockers
+
+- No current blocker.
+- Review tool could not inspect repo files directly due sandbox wrapper limitation, but it reviewed the supplied diff and approved with no findings.