Observer and Tap Contract (Diagnostics-First)
Current scope covers observer/tap behavior at contract, diagnostics, and tests level only. It does not ship a full runtime observer/tap execution engine.
Contract terms
- Checkpoint observer: subscribes to stable, persisted checkpoint outputs.
- Mid-step tap: subscribes to transient step outputs with weaker durability guarantees.
Required diagnostics
Current validator behavior fails fast with explicit diagnostics when:
- a required observer/tap policy token is not in the supported policy token set,
- a requested policy token is missing/blank (treated as unsupported),
- supported policy token configuration includes missing/blank entries (ignored by normalization).
Recommended diagnostic payload fields:
- pipeline name,
- step name,
- requested observer/tap policy,
- supported policy set,
- requested policy token and support decision.
Policy behavior in current scope
- Required observer/tap: configuration error if unsupported.
- Optional observer/tap: explicit warning and skip behavior.
- No implicit fallback that silently changes delivery guarantees.
Test scope for current implementation
- Contract-level validation and diagnostics tests.
- No merge blocker on full runtime tap fan-out execution in current scope.
Out of scope for current implementation
- Dedicated runtime delivery semantics for observer/tap streams.
- Backpressure and durability SLA guarantees beyond existing checkpoint pipelines.
- Checkpoint/non-checkpoint attachment validation.
- Unresolved-step resolution diagnostics.
- Expected-vs-actual output shape diagnostics.