[agent] providers C WP-03: docs, README, self-hosting index, and the per-provider health snapshot

[tyler-dane]

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Milestone: Providers C: closeout
Tracking: #3211
Spec: docs/features/calendar-providers.md
Depends on: #3273, #3275

Goal / finish line

Docs:

• README.md:33 ("See your Outlook events") and :37 ("Outlook and iCloud stay non-goals") contradict :35; :11 and :25 still say Google only. Say Google, Outlook and iCloud.
• docs/self-hosting/README.md links the three provider guides but its mermaid diagram and prose are Google-only and say "push notifications", which is wrong for Apple (poll-only).
• docs/frontend/frontend-runtime-flow.md:199-204 names google-connect-status.util.ts; it is packages/web/src/auth/providers/connect-status.util.ts.
• docs/development/cli.md:41-43 is the only place keyVersion and key rotation are mentioned; link it from docs/self-hosting/server-guide.md next to sync.credentialEncryptionKey.
• docs/features/calendar-providers.md: refresh the Status table row for this milestone and the Named warts list.

Health snapshot (packages/sync/src/telemetry/health-snapshot.service.ts):

• Line 48 hardcodes provider: "google" for the whole fleet, and the four helpers (countConnectionsByState 76-101, summarizeJobs 103-128, summarizeSubscriptions 130-172, summarizeFreshness 174-215) aggregate with no provider filter.
• summarizeSubscriptions counts every Apple resource as missing / neverNotified because Apple is poll-only, which pollutes the counter the August proxy-outage alert relies on (packages/core/src/types/sync/health.contracts.ts:36-42).
• Emit one sync_health_snapshot per registered kind; the contract field stays a single ProviderKind (health.contracts.ts:61). Each helper takes a provider filter. Kinds whose registry capabilities omit changeNotifications report subscription counts as zero by rule (a capability check, not a name check).
• health-snapshot.service.db.test.ts:127 asserts snapshot.provider === "google"; flip it to per-provider assertions with seeded microsoft and apple connections.

Rules: keep Google byte-identical; no provider === "x" branches in domain or web code, use capabilities; no em-dashes in user-facing copy. Line numbers are from main a85f848 (2026-09-05); re-grep before editing. Keep the PR under 60 files and 4000 changed lines or the merge guard downgrades it.

Acceptance

• README and the self-hosting index describe three providers with no contradictions; the diagram shows all three hosts and marks Apple as polling.
• Health snapshot test asserts one row per provider and zero subscription counts for the poll-only kind.
• No em-dashes.

Package scope

docs, sync

Verify commands

bun run verify --strict
bun test:sync

Approval boundary

allow

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