fix(redis): log the ready-wait outcome when a caller is refused

[polylane]

Generated by Polylane Autofix from the review of #60.

When Redis is configured but not ready, abuse-bounding callers wait briefly for the in-flight connection and then fail closed. Nothing recorded that wait's outcome, so an outage and a slow cold start looked the same in the logs. The refusal now emits one warning carrying how long the connection had been pending, whether the wait bound expired, and whether the instance had ever connected.

flowchart LR
  Caller["MCP rate limit or link probe budget"] --> Ready["getReadyRedisClient with caller"]
  Ready -->|"client ready"| Use["use client"]
  Ready -->|"not ready and Redis configured"| Wait["wait for connect up to 1s"]
  Wait --> Recheck{"ready after wait?"}
  Recheck -->|"yes"| Use
  Recheck -->|"no"| Warn["log warning: caller, hasRedisConnected, waitTimedOut, waitDurationMs"]
  Warn --> Closed["caller fails closed"]

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Why this fix

The MCP rate limiter and the link-probe budget both fail closed when Redis is configured but unreachable, after waiting up to a second for the in-flight connect. That wait left no trace: the only warning on this path fires once per episode and carries no fields, so during an incident an operator could not tell a cold start that outran the bound from an instance that never connected.

The refusal now emits one warning that records waitTimedOut, waitDurationMs, hasRedisConnected, and the caller it hit — the MCP bucket name, or the probe batch size. Those fields answer, from the log alone, whether the connect completed but the socket was not ready (a real outage) or was still pending when the bound expired (a cold start that is too slow), and they size the blast radius: one user's write bucket versus a probe batch of twelve. The warning fires once per outage episode, matching the existing once-per-episode warning, so a sustained outage is not amplified into one line per request.

The caller descriptor is a small typed union, so a future caller cannot wait on readiness without declaring which surface it is.

4 files changed (+181/-22)

• lib/collections/link-reachability.ts: modified, +4/-1
• lib/common/redis.test.ts: modified, +108/-3
• lib/common/redis.ts: modified, +65/-17
• lib/integrations/mcp/rate-limit.ts: modified, +4/-1

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Project	Deployment	Actions	Updated
cache-app	Ready	Preview	Sep 19, 2026 12:21pm UTC