feat: Batch 7 — Landing & Observability v1 (#18)

[ghbvf]

Summary

Batch 7 (issue #18): the / Health overview (Landing) and /observe Observability v1, both owned by @gocell/observability (its README scopes it to Landing/Observe). Per the directive, backend gaps are treated as non-blocking — BR-001 (/admin/health/cells), BR-002 (/admin/system), and BR-003 (LGTM) endpoints are unbuilt, so every data path degrades gracefully to an unavailable panel rather than erroring. That degradation is deliverable T703.

Closes #18.

What shipped

• Landing (/) — polled (30s) cell-health card grid + status rollup, SystemInfoCard, intentional deploys/KPI placeholder cards, degraded banner when BR-001/002 are absent, sr-only aria-live refresh announcement. (T701)
• Observability v1 (/observe) — accessible roving-tablist with 3 live tabs (Overview / Logs / Traces) + 4 disabled Wave-2 tabs (Anomalies / What changed / Service graph / Slice health) as aria-disabled spans; each tab is store-driven (real data path) and degrades to the unavailable panel while LGTM is absent; the active panel is wrapped in ObservabilityErrorBoundary (onErrorCaptured). Active tab carried in ?tab=. (T702 + T703)
• @gocell/core i18n gains landing.* + observe.* (zh-CN + en-US; satisfies MessageSchema enforces parity).

Key decisions (confirmed with maintainer)

1. LGTM transport = @gocell/request BFF proxy paths (/api/v1/observability/{loki,tempo,prometheus}/*, BR-003 §3.4 方案 B) — not bare fetch to LGTM origins (方案 A), which would violate the package-boundary no-fetch rule. Forward-compatible with the prod gateway; degrades by default since the proxy isn't implemented.
2. Observe tabs = full v1 — real data rendering on the success path (mocked in tests) + degrade fallback, not empty shells.
3. Promote shared primitives to @gocell/core — useRovingTablist + UnavailablePanel moved from @gocell/devboard into core (business cells can't import each other); all devboard consumers repointed. No back-compat shim.
4. Landing/Observe are auth-gated only (no PDP requiredAction) — operational dashboards for any authenticated admin. / flips to requiresAuth: true (resolves the standing Batch 7 TODO).
5. observe nav stays in the Reserved group with pill: 'preview' (LGTM not deployed); no navConfig change.

AI-robust note

Closes the recalled i18n-missing-key blind spot: i18n.spec.ts now deep-compares the landing/observe leaf-key trees across locales and asserts every key the views render resolves to a non-empty string in both locales (vue-i18n is not key-typed, so a typo'd t() key otherwise passes typecheck/test/build and renders raw).

Packages touched

Package	Change
@gocell/observability (46 files)	new build-out: api (health/system/observe) + lib + stores + components + views + specs
@gocell/core (10)	i18n namespaces + spec; promote useRovingTablist + UnavailablePanel
@gocell/devboard (10)	repoint to core for the two promoted primitives; delete local copies
apps/web (5)	router rewire (/ + /observe), delete HomeView, router/guards specs, e2e/health.spec.ts

packages/contracts/ untouched — no codegen types exist for BR-001/002/003 yet; all backend shapes are local TS types annotated for codegen cutover once the schemas land.

Test plan

• pnpm -w lint — 0 issues
• pnpm -w typecheck — clean (all packages)
• pnpm -w test --run — 1714 passed / 118 files
• pnpm -F @gocell/web build — succeeds; LandingView/ObserveView chunks emitted (subpath exports resolve)
• coverage: @gocell/core 99%+ (gate 90%), @gocell/observability 99% stmts / ~90% branches (gate 80%)
• Playwright e2e/health.spec.ts (degraded/ok health overview, observe tabs, protected /→login redirect) — added + parses; not executed locally (needs server/browsers), runs in CI

Deferred (out of scope, follow-up)

• Wave-2 observe tabs (Anomalies / What changed / Service graph / Slice health) — disabled per PRD §279.
• Real LGTM data UI fidelity tightens once BR-003 lands and the proxy exists.

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