## Problem
When a key returned 401 or 403, the pool marked it permanently
unavailable for the lifetime of that in-memory pool. This is bad UX: a
transient auth failure or a briefly-misconfigured key could take a key
out of rotation until the operator either restarted Coder or
reconfigured the key (even re-saving the same working value).
## Changes
- **403 removed from key failover**: it's a per-request authorization
failure, not a key-level problem, so it's surfaced to the caller as-is
without marking the key or failing over.
- **401 now applies a temporary cooldown** (like 429) so the key
recovers on its own instead of staying blocked.
- When every key is in an auth-failure cooldown, the pool reports a
`502` with no `Retry-After`, but the keys still recover automatically
once the cooldown elapses.
Closes
https://linear.app/codercom/issue/AIGOV-421/ai-gateway-a-quarantined-centralized-key-never-recovers-without-a
Closes
https://linear.app/codercom/issue/AIGOV-533/403s-misclassifying-keys-as-permanently-down-in-ai-gateway
> [!NOTE]
> Initially generated by Claude Opus 4.7, modified and reviewed by
@ssncferreira
Categorises the terminal error of a failed interception and persists it
on the interception record, then surfaces it on the AI Gateway API.
- Categorise into an enum (`bad_request`, `unauthorized`,
`rate_limited`, `overloaded`, `server_error`, `unknown`), unwrapping
the ResponseError envelope, the upstream Anthropic/OpenAI SDK errors,
and key-pool exhaustion so blocking and streaming paths agree.
- Thread the type and raw message through the recorder dRPC into the
`aibridge_interceptions` row (optional proto fields; NULL on success).
- Expose the error on the AI Gateway thread API from the root
interception.
*This PR was produced by opencode (agent) using the `anthropic/claude-opus-4-8` model, under human direction and review.*
Susana Ferreira