gate: released public-surface compatibility (dts, CLI/MCP schemas, daemon RPC, persisted formats)

[thymikee]

Part of #1412 (Track E — gate integrity). From external review: #1417 protects only the .ad grammar. The other released surfaces have existence checks but no compatibility checks — src/tests/package-exports.test.ts proves exports exist and build, not that signatures remained compatible.

Deliverables

• npm declaration surface: diff the public .d.ts surface against the LAST SHIPPED TAG (api-extractor report or an equivalent dts snapshot), with an explicit intentional-break acknowledgment file for major-version changes. Baseline is the released tag, never arbitrary git history.
• CLI --json and MCP structured-output schemas: snapshot representative command envelopes (reuse provider-scenario transcripts as the source of truth) and fail on incompatible shape changes without an ack.
• Daemon RPC: the protocol version already exists (CONTEXT.md, daemon/proxy /health) but nothing enforces bumps. Hash the wire request/response type declarations; a hash change without a protocol-version bump (or an explicit compatible-change ack) fails.
• Persisted config/session formats: fixture files from released versions must load or fail with the intended migration error (same corpus idiom as test: frozen replay-compat corpus with expected verdicts #1417).

Acceptance

• An incompatible public dts change without an ack fails a PR gate naming the symbol.
• A wire-type change without an RPC version bump fails.
• The release process doc gains one paragraph: how baselines roll forward on publish.