Story 1456: FN-RIP — delete the correlation_id machinery (R7d)

Why this exists (the catastrophe it prevents). PRAMAAN ran two request-identity systems side by side: the homegrown correlation_id (cid) — a per-request UUID minted by our own middleware, threaded through a ContextVar, stamped on every log line, ridden on the x-pramaan-correlation-id header, and carried in-message on the agents rail — and the OpenTelemetry trace_id, which is what X-Ray and CloudWatch actually key on. Two id systems that half-overlap is worse than either alone: a human chasing a request has to guess which key the surface in front of them speaks, and the cid was regenerated at the WebSocket edge and ignored by the brain, so it was never continuous end-to-end anyway. The founder decision (2026-06-19, ratified in pramaan-docs ADR-124) is to retire the duplicate while it is cheap — zero customers, no SLA, no compatibility debt — and standardize on W3C trace_id as the single technical request identity. Stories #1453/#1454/#1455 already repointed the error-response field and the app/admin clients off cid; this Story (roster id R7d) is the functions-lane rip-out: the cid machinery itself is deleted so trace_id is the sole correlator.

The Fix: Pull One Whole ID System Out

The cid lived in five shapes — a module, a middleware, a contextvar, log keys, and DTO/health fields. Each is removed at its root, and every importer is cleaned up so nothing references the deleted symbols.

BEFORE                                   AFTER
correlation.py (module + ContextVar)  -> deleted
CorrelationIdMiddleware               -> ErrorTraceIdMiddleware (trace_id-only)
log line { ..., correlation_id, ... } -> log line { ... }              (key gone)
HealthResponse.correlation_id         -> removed
AgentCommand.correlation_id           -> removed   (run_id/traceparent stay)
InvokeMeta.correlation_id             -> removed   (agent_invoke.v1 meta)
WS error body { correlation_id, ... } -> { trace_id, ... }             (repointed)
x-pramaan-correlation-id header read  -> removed

• src/shared/observability/correlation.py (deleted) — the cid module: the UUIDv4 validator, the correlation_id_var ContextVar, and the get/set/reset/resolve helpers. Gone.
• src/shared/observability/middleware.py — CorrelationIdMiddleware becomes ErrorTraceIdMiddleware. The cid resolution, the contextvar set/reset, the route-span correlation_id attribute, and the x-pramaan-correlation-id response header are all removed. The Story-1453 trace-id error-body backfill (_with_error_trace_id + the catch-all 500 envelope) is kept verbatim — the framework-error surface still publishes the active span’s trace_id.
• src/shared/observability/logger.py — the log shape v1 line drops its correlation_id key (and the _log_correlation_id minting helper). trace_id/span_id enrichment from the OTel log instrumentor is unchanged.
• src/shared/dtos/health.py + the two health routes — HealthResponse.correlation_id is removed, and the response_model_exclude={"correlation_id"} guard it required disappears with it.
• src/shared/agent_commands.py, src/shared/agent_contracts/invoke.py — the optional correlation_id field is removed from the queue AgentCommand and from the agent_invoke.v1 InvokeMeta. The brain already ignored cid, so dropping the producer field is safe; traceparent/run_id carry identity forward.
• src/app_api/router_ws.py — the WS Lambda stops resolving/setting cid and stops stamping it on the envelope. The WS error body field is repointed from correlation_id to trace_id (sourced from get_current_trace_id()), matching the #1453 error surface.
• src/clerk_worker/{handler,runner}.py, src/rail_canary/handler.py, request/payload loggers, metric helpers — every remaining cid read, contextvar token, log field, and metric-metadata key is removed. The SQS traceparent extraction and manual_span trace context in the worker are left intact.
• openapi/app-api.json, openapi/admin-api.json — regenerated via make openapi; the correlation_id property is gone from both Health schemas, no other drift.

Why the Agents Rail Had To Be Swept Too

It would have been smaller to delete only correlation.py and the middleware. That fails to compile: router_ws, the clerk worker, and the rail canary all imported the cid helpers. Deleting the module forces removing every importer — which is exactly the point. The acceptance bar is grep-zero cid in src/, not “the obvious files only.” A half-removed id system leaves dangling imports and a log key that some surfaces emit and others don’t — the precise two-systems-half-coexist mess EPIC-1400 exists to end.

Acceptance Evidence