[Stephen Belanger (Qard)]

Stage extraction and completion-preserving messages establish the contracts for the recoverable pipeline. Delivery<T> retains its completion obligation through mapping and forwarding; terminal extraction confirms event checkpoint persistence. Plugin outcomes describe results without naming successor stages.

Braintrust sinks enable checked delivery and own a queue per routing branch, preventing a rejected sibling batch from poisoning another route's flush. Rejected flushes invalidate the actor's contiguous checkpoint boundary so consumed failed batches remain eligible for journal replay. Deferred delivery and checkpoint-write failures can still complete later. This layer preserves event replay; automatic recovery comes in subsequent layers.

The SDK pin uses the merged braintrust-sdk-rust#106 commit f2216fa0ceee132e02f1392c0e5af89ae762e9c8, with the matching Cargo.lock revision. Unused channel-port traits are deferred to the next layer; dead-code allowances cover only individual methods and a field.

Stacked on #194, which isolates doctor tests from installed settings, and main at 98051a5, including production unwrap/expect bans, security dependency updates, and all-span provenance. Main's expanded provenance coverage replaces the former root-only sink test.

Pipeline layer 1 of 9; base: #194.

Validation at 3514528: all 513 tests pass in the locked all-feature Rust suite without exclusions or environment overrides; five live-agent tests remain normally ignored. Strict all-target/all-feature Clippy, formatting, and diff checks pass. Restacked on #194 at b2c24be; fresh remote CI is pending.

SDK dependency update at 2c4e7be: strict Clippy, formatting, and diff checks pass. The local full-suite attempt stopped at stalled_initialize_keeps_cursor_tool_observation_fail_open; further validation is delegated to CI as requested.

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-13T16:15:23.558614Z	b6119ce	Draft marked ready

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Reviewed commit: b6119ce0c3

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[Abhijeet Prasad (AbhiPrasad)]

we should make sure we bump rust sdk dep before merging in all these prs