Make MCP campaign execution trackable and non-blocking

[Ankit6149]

Foundation slice for #35 and #36.

Implemented and verified:

• in-process MCP campaign execution registry with stable execution IDs
• queued/running/completed/failed/cancelled state truth
• start/status/cancel campaign workflow tools
• cancellation propagated into the active HTTP request
• global JSON-RPC serialization removed so ping/tools/status/cancel remain responsive during long generation
• execution-registry, workflow-tool, cancellation, failure-isolation, and real stdio concurrency regression tests

Verification:

• exact-head GitHub CI #1033: success
• Vercel correctly skipped the non-production deployment under the storage policy

Not complete:

• full MCP workflow parity ([P1][Plan 2] SF-036 — Expand MCP into a complete campaign workflow #35)
• per-campaign ordering and independent-campaign concurrency ceilings ([P1][Plan 2] SF-037 — Prevent long MCP generation from blocking unrelated requests #36)
• durable generation job state / cross-process recovery
• complete request-budget/cost controls ([P1][Plan 2] SF-017 — Add request, context, concurrency, and cost controls #34)
• full web generation progress/cancellation acceptance ([P0][Plan 2] SF-006 — Replace destination burst with bounded generation concurrency #27)

This PR intentionally does not close those issues.

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1 Skipped Deployment

Project	Deployment	Actions	Updated
signal-flow-studio	Ignored		Sep 21, 2026 8:33pm UTC