fix(observability): attribute outage refusals to caller, bucket, and probe count

[polylane]

Generated by Polylane Autofix from the review of #60.

When Redis is unreachable the MCP surface refuses requests and the link prober stops probing, and the events those refusals produced could not be tied to a caller or a scope. The refusals now record the affected user, the rate-limit bucket, and the number of probes turned away, so an operator can see who an outage is affecting while it is happening.

Why this fix

While Redis is unreachable the MCP surface fails closed, so every affected caller gets an error and nothing is written. Those refusals were unattributable. rate limit unavailable; rejecting request carried no fields at all, and the counter-failure warning below it carried the bucket and the error but no user. An operator looking at an outage therefore saw a count of refusals and could not tell which tokens were hit, whether one heavy caller dominated, or whether the write bucket was the one being refused. Both sites now carry userId and bucket, so "who is being refused right now, and on which scope" is answerable from the log stream while the outage is live.

The link-probe refusals had the mirror gap: they named the user but not the probe count, so the amount of outbound fan-out the refusal prevented was invisible. Both refusal warnings now carry amount, which separates a refusal that stopped a handful of probes from one that stopped a large fan-out.

These are field additions to existing events: no new log sites, no level changes, no message changes, so nothing that currently clusters by message changes shape. userId, bucket, and amount are plain values that the shared formatter does not redact, and no payload, URL, or credential is added.

The refusals themselves remain the intended fail-closed policy; this change only makes them attributable. Any operator complaint that the outage is still visible is a Redis-health question rather than a code change here.

3 files changed (+12/-3)

• app/mcp/route.ts: modified, +9/-3
• lib/collections/link-reachability.ts: modified, +2/-0
• lib/integrations/mcp/rate-limit.ts: modified, +1/-0

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Project	Deployment	Actions	Updated
cache-app	Ready	Preview	Sep 19, 2026 8:04am UTC