…crub (#1250)

PR #1248's Redis-backed dedup throws inside cascade-worker processes:

  ERROR Review-dispatch dedup Redis call failed — failing closed
    error: 'Error: REDIS_URL is required for review-dispatch dedup'

Confirmed live at 2026-05-01T17:25:44 in worker
`cascade-worker-coalesce_ucho_MNG-461_*`. Sentry tag: `review_dedup_redis_down`.

Root cause: `src/utils/envScrub.ts:13-18` lists REDIS_URL in
`SENSITIVE_ENV_KEYS`. Worker-entry calls `scrubSensitiveEnv()` early in
startup, which does `delete process.env.REDIS_URL` to keep infra secrets
out of agent-spawned subprocesses. The dedup module reads
`process.env.REDIS_URL` lazily at first dispatch — well after the scrub —
so it sees `undefined` and throws. The fail-closed handler returns false,
and the post-completion-hook silently logs `Skipping post-completion
review: already dispatched` (which looks identical to the working dedup's
"correctly rejected duplicate" log, hence the bug evaded the prod canary).

Why it didn't bite immediately: the post-completion-hook short-circuits
when CI isn't all passing at impl exit
(`agent-execution.ts:269-275`), so the bug only triggers on the narrow
timing where CI is fully green BEFORE impl finishes. Small fraction of
runs.

Why router is unaffected: cascade-router never calls scrubSensitiveEnv.
PR #196's review (verified 1-run earlier) was dispatched from the router
via check-suite-success — that path was never broken.

Fix: read the URL via `routerConfig.redisUrl` instead of
`process.env.REDIS_URL`. routerConfig is captured at module-load time in
`src/router/config.ts:137-138`, well before scrubSensitiveEnv runs. The
cached value survives the scrub the same way the DB pool's cached
connection string does — exactly the pattern envScrub.ts's docstring
describes.

Two-line source change + new regression-pin test that claims, deletes
process.env.REDIS_URL, and claims again — both must succeed (second
deduped) without throwing `REDIS_URL is required`.

Verification: vitest 2497/2497, typecheck clean, lint clean.

Out of scope (follow-up): `src/queue/cancel.ts` has the same
`process.env.REDIS_URL` lazy pattern but is only called from cascade-router
and cascade-dashboard (neither scrubs env), so it doesn't bite today.
Apply the same routerConfig swap for symmetry in a separate PR.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>