chore(openspec): archive gate-sentry-spans and sync observability spec

Moves the completed change to openspec/changes/archive/ and creates the canonical openspec/specs/observability/spec.md. Co-authored-by: Cursor <cursoragent@cursor.com>
2026-07-16 13:07:13 -06:00
parent a5c83ee026
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+# observability Specification
+
+## Purpose
+TBD - created by archiving change gate-sentry-spans. Update Purpose after archive.
+## Requirements
+### Requirement: Error monitoring is always active
+
+The system SHALL report runtime errors to Sentry whenever `SENTRY_DSN` is configured, independent of any tracing configuration. This includes REST, WebSocket feed, and SSE errors captured via `Sentry.captureException`, plus process-level `unhandledRejection` and `uncaughtException` handlers.
+
+#### Scenario: Error captured with DSN set
+
+- **WHEN** `SENTRY_DSN` is set and a handled error occurs on the WebSocket, REST, or SSE path
+- **THEN** the error is sent to Sentry as an error event
+
+#### Scenario: No DSN configured
+
+- **WHEN** `SENTRY_DSN` is empty or unset
+- **THEN** Sentry is not initialized and no events are sent, and the application continues running normally
+
+### Requirement: Tracing spans are gated by an environment flag
+
+The system SHALL only create and export OpenTelemetry spans when the `SENTRY_TRACING` environment variable is enabled AND `SENTRY_DSN` is set. The flag SHALL default to disabled so that continuous 24/7 operation emits zero spans by default.
+
+#### Scenario: Tracing disabled by default
+
+- **WHEN** `SENTRY_TRACING` is unset or falsy (default)
+- **THEN** the tracer is a no-op, no spans are created on the hot path, and no spans are exported to Sentry
+
+#### Scenario: Tracing enabled with DSN
+
+- **WHEN** `SENTRY_TRACING` is truthy and `SENTRY_DSN` is set
+- **THEN** hot-path spans (`ws.message`, `orderbook.process`, `arbitrage.evaluate`, `sse.broadcast`) are created and exported to Sentry, and `tracesSampleRate` is applied
+
+#### Scenario: Tracing enabled without DSN
+
+- **WHEN** `SENTRY_TRACING` is truthy but `SENTRY_DSN` is empty or unset
+- **THEN** the tracer is a no-op and no spans are exported, since export requires a DSN
+
+### Requirement: Error capture is preserved when tracing is disabled
+
+The system SHALL continue to report exceptions thrown inside hot-path work wrappers to Sentry even when tracing is disabled, so disabling spans never reduces error visibility.
+
+#### Scenario: Exception in hot-path wrapper with tracing off
+
+- **WHEN** `SENTRY_TRACING` is disabled and code wrapped by the hot-path span helper throws
+- **THEN** the exception is still captured and reported to Sentry (as an error), and re-thrown to preserve existing control flow
+