[finding] check-drift-comment.mjs has no fixture that reaches the SDK-bridge line, so that bullet's rendered bytes — the cause split included — are pinned only by source grep #12148

Observed while implementing #11867 (PR #12146). Filed unassigned for grading. ⛔ Not a claim on anyone's time.

The reading

scripts/docs-audit/check-drift-comment.mjs is the repo's end-to-end pin on what the docs-drift comment actually says: it runs real fixture diffs through the real affected-docs.mjs and the real github-script block, then asserts on the posted bytes. Its own header states why that shape was chosen — a source grep "would pass on text that is never REACHED".

None of its five fixtures reach the SDK-bridge line. That is deliberate and documented:

// `MAX_WIDGETS` is the anchorable symbol on purpose — an ALL-CAPS name is excluded from
// the sdk route bridge, so these repos (which declare no route ledger) do not trip the
// bridge's broken-scan verdicts and the fixture stays about the headline.

The consequence is narrow and worth recording: the bridge bullet in the fold — now the longest single line the comment renders, carrying reachable / clientRows / unreachable and, since PR #12146, the three-way cause split — has its existence pinned by source grep in affected-docs.mjs --self-test (/bridge\.causes/, /parts === bridge\.unreachable/) but its rendered bytes pinned by nothing. Every other verdict that comment produces is byte-pinned by this harness; this one is not.

What that does and does not cost

• It is not unpinned: the source pins go red if the render branch, the partition guard, or the advisory ceiling is removed, each reverse-verified in PR fix(docs-audit): measure the bridge cause split on the advisory path and render it in the drift comment #12146.
• What no pin can see is a change that keeps those tokens and still renders wrong — a template-literal typo, a bucket printed under the wrong label, the guard inverted so the split renders exactly when it should be withheld. On this line specifically, the withheld and unmeasured arms were verified in PR fix(docs-audit): measure the bridge cause split on the advisory path and render it in the drift comment #12146 only by hand, against synthesised payloads, and that verification does not persist.

The shape, if taken

A sixth fixture whose repo declares a *-route-ledger.ts and a registrar file, with a non-ALL-CAPS changed symbol, so the bridge runs and the bullet renders. Cost worth pricing before committing: such a fixture must not trip brokenScan, so its ledger has to be spelled the way parseLedgerSource reads (single-quoted route: / client:), and the existing comment's reasoning for avoiding the bridge is exactly that this is fiddly. A cheaper variant that pins the arms without a ledger: drive renderComment from a synthesised affected.json rather than a git fixture — weaker, since it no longer rides the real mapper, but it would pin the three arms' bytes.

Not claimed

• No opinion on whether this is worth a fixture. The harness's cost-of-entry is real and the source pins are not nothing.
• Whether the other unpinned fold lines (crossCutting, overbroad, weak) are in the same position was not checked — this was noticed about the bridge line only.

Refs

#11867 · PR #12146 (where the cause split reached this line) · #11357 (the harness and why it spawns fixtures) · #9433 (the half-wired-key rule)