build(sdk): check in operation descriptors and drop build.rs

[devin-ai-integration]

Summary

• Delete crates/tracedecay-sdk/build.rs and its [build-dependencies]. src/operations.rs is checked in again, generated through the same contracts:generate path as the TypeScript SDK.
• Add a drift test, codegen::tests::checked_in_rust_operations_match_canonical_registry, and extend contracts:check so it also compares operations.rs.

Motivation

build.rs made tracedecay-contracts, -domain, -policy and -tool-catalog build dependencies. The host graph resolves different features for them than the normal graph does (for example, serde_json raw_value vs preserve_order, and schemars chrono04). As a result, Cargo compiled that spine a second time on every cold build. Pinning profiles does not fix this, because the duplicate units come from the feature differences.

This undoes part of 0f6784d, which moved the descriptors into OUT_DIR so there would be no checked-in copy that could drift. Drift is now a hard test failure instead.

A/B: cold cargo build -p tracedecay-cli --timings --locked, workspace packages cleaned, third-party crates cached, 8 cores, one run each:

	units	wall	CPU (workspace)
master (7aa7877)	846	470s	1999s
this PR	797	473s	1682s (+34s third-party rebuilt after the feature change)

The change saves about 317s of workspace CPU (about 16%) and removes 49 units. Wall time on 8 cores does not change, because the critical path goes through tracedecay, not the SDK. The saving matters on machines with fewer cores and on parallel CI jobs. tracedecay-sdk itself now starts at 94s instead of 163s.

Changes

• src/codegen.rs: write_sdk_sources writes crates/tracedecay-sdk/src/operations.rs along with the TS sources. It renders everything before writing anything. The rendered Rust file has a module doc and #![cfg_attr(rustfmt, rustfmt::skip)], so no rustfmt step is needed. Its body is byte-identical to the previous OUT_DIR output.
• src/bin/generate.rs: calls write_sdk_sources. The dead_code allow is no longer needed.
• dashboard/codegen/src/cli.ts: exportSdkSources also returns operations.rs, so contracts:generate writes it and contracts:check compares it.
• AGENTS.md: lists operations.rs among the generated files.

Test plan

• cargo fmt --all -- --check
• cargo clippy -p tracedecay-sdk --all-targets --locked -- -D warnings and cargo clippy --all-targets --locked -- -D warnings in sdks/codegen
• cargo test -p tracedecay-sdk --lib (10 passed), cargo test --locked in sdks/codegen (13 passed)
• Drift test fails as expected after hand-editing one DeadlineBehavior in operations.rs: "crates/tracedecay-sdk/src/operations.rs is stale; run pnpm --dir dashboard run contracts:generate"
• pnpm --dir dashboard run contracts:check: "contracts up to date"
• cargo tree -p tracedecay-sdk -e build shows no build dependencies

Checklist

• CHANGELOG.md updated (build-internal, no user-facing change)
• No secrets, credentials, or .env files included
• Breaking changes documented (none)

Link to Devin session: https://app.devin.ai/sessions/4b9be38fe30b4b79a456673a3ad33483
Open in Devin Desktop: https://app.devin.ai/desktop/session/4b9be38fe30b4b79a456673a3ad33483?variant=devin
Requested by: @ScriptedAlchemy

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[devin-ai-integration]

I'll fix CI failures and address comments from users with write access. I'll skip comments containing "(aside)".

• Disable automatic comment, CI, and merge conflict monitoring

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[devin-ai-integration]

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