fix(firestore-bigquery-change-tracker): unmask BQ errors and stop spurious table updates

[cabljac]

Summary

Two small but high-impact fixes in firestore-bigquery-change-tracker. Both bugs were diagnosed in detail by the issue reporters with the offending lines called out.

• Fixes 🐛 [firestore-bigquery-export] handleFailedTransactions crashes on warm containers, masking real BigQuery errors #2801 - `handleFailedTransactions` crashes on warm containers, masking the original BigQuery error
• Fixes 🐛 [firestore-bigquery-export] tableRequiresUpdate always returning true #2194 - `tableRequiresUpdate` always returns true (clustering = null, and `pathParamsColExists` undefined)

#2801: dead-letter path crashes on warm containers

bigquery/handleFailedTransactions.ts called db.settings({ ignoreUndefinedProperties: true }) inside the exported async body. The Firestore Node SDK contract requires settings() be called at most once and before any other method runs on the singleton. On warm Cloud Functions containers both conditions are violated by the second invocation; the resulting Firestore has already been initialized throw masks the real BigQuery insert failure that put us on the dead-letter path in the first place.

Fix: guard with a per-instance `Set`, plus a `try/catch` so that even if the singleton was used elsewhere in the process before this module's first call, the dead-letter write to the backup collection still proceeds and the real BQ error surfaces upstream.

#2194: `tableRequiresUpdate` always returns true

Two independent bugs in the same function:

1. Clustering check:
   ```ts
   const configCluster = JSON.stringify(config.clustering); // "null" when unconfigured
   const tableCluster = JSON.stringify(metadata.clustering?.fields || []); // "[]"
   if (configCluster !== tableCluster) return true; // always true
   ```
   Fixed by normalising null/undefined to `[]` before stringifying: `JSON.stringify(config.clustering || [])`.

2. `pathParamsColExists` strict-equality against `undefined`:
   `bigquery/index.ts` assigned the result of `fields.find(...)` (which is `Field | undefined`) to a parameter typed `boolean`. The check `!!config.wildcardIds !== pathParamsColExists` then resolved to `false !== undefined` -> always true.
   Fixed by coercing in the caller (`!!fields.find(...)`). Applied to `documentIdColExists` and `oldDataColExists` too since the function signature already promises `boolean` for all three (downstream checks happened to tolerate `undefined` for those two, but the type was being violated).

Test plan

• `npm run build` (`tsc`) clean in `firestore-bigquery-export/firestore-bigquery-change-tracker`
• CI integration tests against the configured BQ project (the existing `tests` directory hits a real BQ dataset; not runnable locally without `PROJECT_ID` and credentials)

The diff is intentionally tight (3 files, +23 / -8). I haven't added new integration tests since they all target a live BigQuery project; happy to add unit-level mocks for both fixes in a follow-up if reviewers prefer.

[gemini-code-assist]

Code Review

This pull request improves the robustness of the BigQuery change tracker by handling undefined clustering configurations and safely applying Firestore settings during failed transactions to avoid runtime errors. It also ensures boolean values for column existence checks. Feedback suggests enhancing type safety for the Firestore instance ID and using the more idiomatic Array.prototype.some() method instead of !!find() for checking the presence of specific columns.