docs: keep notices fresh at commit time instead of a new CI gate

Regenerate THIRD_PARTY_NOTICES.md from a pre-commit job whenever a
manifest, lock file, vendor manifest, or pyproject is staged, and assert
the committed bytes inside the generator spec the test lane already runs.
Drops the separate doc-sync gate: no extra CI process, and a dependency
edit no longer bounces back from CI to rerun a generator.

.agents/notes/implemented/process/2026-07-30-generated-third-party-notices.md

@@ -8,11 +8,13 @@ English | [中文](2026-07-30-generated-third-party-notices.zh.md)
 
 Open-sourcing this repository requires disclosing the third-party software it depends on, with each project's license. The disclosure has to be complete, has to stay true as dependencies change, and has to say something a reader can act on — which of these packages end up on a user's machine, and which only build and test the repository.
 
-A hand-written inventory answers none of those durably. Roughly a hundred rows of names and license strings derived from manifests drift silently the moment a package is added, removed, or relicensed, and nothing in `doc-sync` would notice.
+A hand-written inventory answers none of those durably. Roughly a hundred rows of names and license strings derived from manifests drift silently the moment a package is added, removed, or relicensed, and nothing would notice.
 
 ## Decision
 
-[`THIRD_PARTY_NOTICES.md`](../../../../THIRD_PARTY_NOTICES.md) is generated by [`scripts/gen-third-party-notices.ts`](../../../../scripts/gen-third-party-notices.ts) from the workspace manifests, `vendor/README.md`, the `pyproject.toml` files, and `pnpm-workspace.yaml`. `pnpm run verify-third-party-notices` runs the generator with `--check` as a `doc-sync` leaf gate, so a dependency change that skips regeneration fails the same way a stale catalog does. The root README pair links the file from its License section.
+[`THIRD_PARTY_NOTICES.md`](../../../../THIRD_PARTY_NOTICES.md) is generated by [`scripts/gen-third-party-notices.ts`](../../../../scripts/gen-third-party-notices.ts) from the workspace manifests, `vendor/README.md`, the `pyproject.toml` files, and `pnpm-workspace.yaml`. The root README pair links the file from its License section.
+
+**Freshness is maintained, not merely enforced.** A pre-commit job regenerates the file and stages it whenever a manifest, lock file, `vendor/README.md`, or `pyproject.toml` is staged, so an unrelated dependency edit never has to come back and rerun a generator. The committed bytes are then asserted inside [`scripts/gen-third-party-notices.spec.ts`](../../../../scripts/gen-third-party-notices.spec.ts), which the test lane already runs — the check adds no gate process, no scheduler slot, and no separate CI step. `pnpm run verify-third-party-notices` remains available for a standalone check.
 
 The file discloses **direct** dependencies only. The complete npm closure with pinned versions already lives in `pnpm-lock.yaml` (`pnpm licenses list` renders it) and the Python closure in `python/sdk/uv.lock`; re-materializing either as prose would be a second, worse copy.
 
@@ -24,12 +26,14 @@ License and repository metadata come from the installed pnpm store, so the gener
 
 ## Testing
 
-[`scripts/gen-third-party-notices.spec.ts`](../../../../scripts/gen-third-party-notices.spec.ts) pins the tiering rule against fixture manifests — including the two cases that motivate it, a `dependencies` entry of a test-support package and a plugin package no app mounts — and pins that the vendored-table parser reads the committed manifest and yields nothing when the table shape changes, which is what makes the generator fail loud rather than emit an empty section.
+The same spec that asserts freshness pins the tiering rule against fixture manifests — including the two cases that motivate it, a `dependencies` entry of a test-support package and a plugin package no app mounts — and pins that the vendored-table parser reads the committed manifest and yields nothing when the table shape changes, which is what makes the generator fail loud rather than emit an empty section.
 
 ## Alternatives considered
 
 **Keep the hand-written file and review it at release time.** Reviewing a hundred derived rows by eye is exactly the work a generator does correctly, and the file's own claim — that it lists every direct dependency — would be unverified between releases.
 
+**Verify through a dedicated `doc-sync` gate.** That is how every other generated artifact here is checked, and it was the first shape of this change. It costs a gate process and a scheduler slot in a matrix that is already long, and — worse — its only failure mode is telling a contributor, minutes after they pushed an unrelated dependency bump, to go rerun a generator. Regenerating at commit time removes the interruption, and the assertion inside a spec the test lane already runs keeps the guarantee at no additional CI cost.
+
 **Enumerate the full transitive closure.** The closure is thousands of packages, already recorded in the lock files with exact versions, and would bury the direct dependencies that a reader actually evaluates. The file points at the lock files and the `pnpm licenses list` renderer instead.
 
 **Tier by manifest section (`dependencies` vs `devDependencies`).** Mechanically simple and wrong on real data in both directions, as the tiering paragraph above records.
@@ -40,7 +44,7 @@ License and repository metadata come from the installed pnpm store, so the gener
 
 ## Consequences
 
-Adding or removing a dependency now requires running `pnpm run gen-third-party-notices` and committing the result; `doc-sync` fails otherwise. That is the intended cost — the disclosure cannot silently go stale.
+A dependency edit now carries a regenerated notices file into the same commit. Contributors pay one generator run — about a second — on commits that touch a manifest, and nothing on any other commit. Committing with hooks disabled defers the cost to a test-lane failure that names the command.
 
 The generator needs an installed tree, which makes it heavier than a pure-source generator, and a new package with unusable published metadata needs an `OVERRIDES` entry rather than silently rendering a blank license. Both failures are loud and name the remedy.