contract.json is the shared list of SDK recorder names, instrument types, units and tag keys for PHP, Python and Rust. It captures the inspected Python recorder surface. Implementation, installed acceptance and exporter-guide delivery remain separate from publishing this list.

Rust's recorder and optional Prometheus adapter have an installed-package receipt and exporter guides in all eight locales. Python's recorder correction and Prometheus adapter have a normal registry-installed receipt and a published metrics and exporter reference. PHP implementation, emitted worker-task controls, installed acceptance and exporter guidance stay open in #233. One SDK's delivery does not establish another SDK's adoption.

Consumers should pin the contract's Git commit. SDK tests load that one list and compare observations from their actual client and worker recorder hooks. Offline tests may vendor its exact JSON bytes with the upstream commit and SHA-256 recorded and verified. Update that copy from the shared contract, without a second hand-maintained language-specific vocabulary. The reference commit identifies the inspected implementation, not a required package version or release qualification.

The client and worker accept a recorder with increment(name, value, tags) and record(name, value, tags) operations. Language-specific method spelling may differ. The default recorder discards observations. The worker uses its explicit recorder, otherwise its client's recorder, otherwise the no-op.

Each observed operation increments its counter by one and records one nonnegative monotonic duration in seconds with the same tag map. Unit 1 is a count, and s is seconds. Tags are strings and tag ordering is immaterial. Only the listed tag keys belong to each core metric. Exporters may add resource labels separately. Recorders should be fast and must handle their own exporter failures without throwing into the client or worker.

These counters describe process observations. They are not durable execution counts, exactly-once receipts, billing units or schedule-to-start latency. Missing observations are not zero or healthy. Abrupt process loss can prevent the final observation.

Client metrics have method, route, plane, status_code and outcome:

• method is the uppercase HTTP method. route uses reviewed path templates without the /api prefix or query string. For example, /workflows/{workflow_id}/signal/{name} and /schedules/{schedule_id} preserve the Python reference's placeholders.
• plane is control or worker, according to the credential plane used by the request. Discovery using a worker credential uses worker.
• status_code is the response's decimal status string, or none when no response status was recorded.
• outcome includes ok, http_error and bridge_rejected. Other caught failures use language-specific exception or error categories. The pinned Python reference can also retain pending when cancellation bypasses its ordinary exception handler. These values are not an exhaustive portable error taxonomy. Dashboards should not assume those categories match between languages.

Worker metrics have task_kind, task_queue and outcome:

• task_kind identifies workflow, activity, query or supported update_validation work. Unsupported task kinds do not create new SDK capabilities merely because they appear here.
• task_queue is the configured queue name. Applications should use bounded queue naming rather than a new queue per run.
• Poll outcomes include task, empty, backpressure and error. Task outcomes describe processing, such as completed, failed, expired or approved, and can differ by task kind. Keep a task's outcome separate from its workflow's eventual terminal state.

Core tags must not contain workflow, run, task, worker or session IDs, payloads, credentials, exception messages or raw URLs. Use placeholders for variable path segments, and a bounded unknown route value for an unrecognized operation. Queue names remain application-controlled. Exporter resource labels need their own cardinality and privacy review.

The pinned Python reference predates normalization of update-validation task and worker-session routes and retains literal IDs there. Those values are not approved tag shapes. The correction has separate published-package and normal registry-installed acceptance. Use that receipt and the installed package's guide when qualifying consumers. The JSON retains its original reference and records the inspected metric names, instruments and tag keys. It does not certify bounded values or cross-SDK adoption. Additional operations need explicit normalization and outcome review.

The names in the JSON file are recorder names. A Prometheus counter exporter can append _total, and a histogram exporter produces its normal bucket, sum and count series. Those exporter conventions do not rename the recorder contract. OpenTelemetry adapters use the listed instrument type and unit. Histogram buckets, exporter resource labels and transport configuration are application choices.

Treat adopted names, types, units, tag keys and their meanings as stable SDK API. Renaming/removing a metric or tag key, changing an instrument or unit, or changing an existing metric's required tag set needs an SDK major release and migration guidance. Announce additional metrics and new or changed tag values in the SDK changelog. An incompatible contract uses a new schema identity. Compatible additions increment revision and preserve existing entries. Python's current exception-type outcomes remain language-specific.

Each SDK must exercise its actual recorder on successful and failed requests, transport retry, normalized routes, empty/delivered/error/backpressure polls, and supported task success/failure paths. Check the names, recorder operations, tag keys and string values against the pinned contract. Require a counter increment of one and a matching nonnegative duration observation for each completed observed operation. Compare deterministic outcomes between SDKs, while keeping language-specific exceptions explicit. Exercise default no-op, client-to-worker inheritance and an explicit worker override.

Include variable-ID route pairs for workflow/run/task/worker/session operations, queries containing synthetic secrets and unknown paths. Changing an ID or query must not create a new route series or expose its value. Never replace this check with an assertion that the tag key is merely named route.

Use installed-package checks for the published adapters and examples. Record each SDK's package and guide results on #233, preserving the completed Rust and Python receipts and PHP's remaining work. Source inspection and this contract's tests do not provide that runtime evidence.