MCP: Verify the deployed service and prepare rollout #2634

Tracking issue: #2408. Depends on #2625, #2626, #2630, #2633, #2635, #2642 and #2643, with authorization-service readiness evidenced by the full-flow qualification.

Tracking correspondence: L4 deployed verification and L6 operations. User onboarding is #2643 (L5). Shared requirement IDs remain stable across the delivery plan and #2408.

Outcome

Bring the OAuth-protected modern MCP endpoint to market with deployed qualification and rollout evidence. The replica-routing failure in #2500 is addressed by removing MCP sessions, then proving calls are independent through the actual edge. A local smoke test alone does not establish release readiness.

Deployed qualification

• Deploy the exact qualified artifact and record its digest, environment, dependency versions and client builds. Run the independent client and raw HTTP cases through the public endpoint.
• Verify reachable protected-resource metadata, correct public issuer/resource URLs, challenge visibility and forwarding of Authorization, MCP-Protocol-Version, Mcp-Method and Mcp-Name. Verify Origin/CORS and any enabled JSON/POST SSE response streams.
• Exercise successive requests across replicas and pod replacement without sticky-session dependence or initialize. Test disconnect and ambiguous completion without unsafe write replay.
• Older protocol revisions must fail. Unknown future revisions fail until qualified. Old Token/token/X-Cassandra-Token credentials and manually supplied AstraCS bearer tokens must not authenticate MCP. Test wrong issuer/audience/organization, insufficient scopes, expiry, revocation and recovery with valid OAuth.
• Verify disabled-MCP and optional-capability behavior. Operational logs must not contain payloads, access/refresh tokens, authorization codes, PKCE verifiers or registration secrets.

Operations and rollout

• Supply the operator runbook and support escalation path to MCP: Publish connection and migration instructions #2643 while deployment work is in progress. MCP: Publish connection and migration instructions #2643 owns user onboarding, migration instructions and the published client matrix.
• Record baseline latency/error metrics, numeric promotion and rollback thresholds, release owner and operational runbook. Set thresholds from measurements.
• Rollback must preserve the OAuth-only boundary and explicit modern version policy. Pause or disable MCP if the available rollback artifact would restore forbidden access or old-client behavior.

Done when

The exact release artifact passes deployed auth, modern-protocol, client, replica/pod-replacement and credential-safe logging checks. #2643 provides reviewed onboarding evidence. Record promotion/rollback approval and unresolved nonblocking follow-ups.

This ticket owns L4 deployment and L6 operations. It supplies a runbook to #2643 before promotion, so documentation does not have to wait for this ticket to close. A package bump or a successful tool call is not release completion.

Changelog traceability

• M1 Remove protocol sessions, lines 12 — Required.
• M4 Use POST subscriptions for change events, lines 18 — Conditional.
• M9 Remove stream redelivery, lines 28 — Required.
• m4 Validate standard HTTP headers, lines 35 — Required.
• m7 Validate authorization response issuer, lines 38–41 — Required auth.
• D2 Retire the old HTTP plus SSE transport, lines 82–85 — Required.

Normative detail: Streamable HTTP, authorization, caching.