@hulumi/drift: Drift classifier fails open on adapter errors and over-promotes Mixed verdicts

**Affected:** `@hulumi/drift` `< 1.4.0` — **Fixed in:** `1.4.0` — **Severity:** Medium — **CWE-755 (Improper Handling of Exceptional Conditions)** #### Summary `@hulumi/drift` runs four adapters that each ask a different question about whether a resource has drifted (Pulumi-state diff, provider-version change, CloudTrail event, etc.). A classifier combines the adapters' answers into a verdict like `None / none`, `ConsoleBreakGlass / high`, or `Mixed / high`, and caches the verdict for 6 hours by default. Two related bugs from one root cause — the classifier only read each adapter's `detected: true/false` field and ignored whether the adapter itself succeeded: 1. **Cached "all clear" on adapter failure.** When an adapter failed (e.g. transient network error from the Automation API), the classifier read `detected: false`, concluded "no drift", and cached the verdict as `None / none` for 6 hours. A single transient failure could mask real console-break-glass mutations for the rest of the window. 2. **Mixed verdicts without real evidence.** The `Mixed / high` and `ConsoleBreakGlass / high` verdicts (incident severity) could fire on the "the CloudTrail probe round-tripped successfully" signal rather than actual evidence that anything had been changed via the console. Normal provider-API churn could end up falsely escalated to incident severity. #### Impact Consumers running drift detection in CI / cron could see transient adapter failures silently cached as "all clear" — masking real attacks for up to six hours — or see ordinary provider-version churn falsely promoted to incident severity. Either way, the verdict source was unreliable for downstream incident workflows that gate on it. #### Patches Upgrade to `@hulumi/[email protected]`. Classifier-only fix (the TLA+-verified 6-row verdict matrix is byte-identical): - adapter failures now fail closed to `Unknown / low`, and degraded verdicts are not written to the cache; - the `Mixed` / `ConsoleBreakGlass` promotion now requires real CloudTrail event evidence rather than probe liveness. #### Workarounds Setting `options.minConfidence: "medium"` on the classifier call prevents the degraded `None / none` from being cached (it doesn't meet the threshold), partially mitigating case (1). No workaround for case (2). #### Resources - [PR #178](https://github.com/kerberosmansour/hulumi/pull/178) (Cluster D); regression tests in `packages/drift/tests/classifier-fail-closed.test.ts`.

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