## Description
Adds automatic key failover for passthrough routes for the Anthropic and OpenAI providers. A new `keyFailoverTransport` wraps the reverse-proxy transport: centralized requests walk the configured key pool and retry with the next key on key-specific failures (401/403/429), reusing the same key-marking semantics as the bridged routes.
BYOK passthrough requests run as a single attempt with no failover.
## Changes
- New `keypool.KeyFailoverConfig` carrying the `Pool` to walk and the provider-specific closures (`IsBYOK`, `InjectAuthKey`, `MarkKey`, `BuildExhaustedResponse`).
- New `keypool.NewKeyFailoverTransport`: wraps an inner `http.RoundTripper`. Returns `inner` unchanged when `Pool` is nil, otherwise produces a transport that buffers the request body once, walks the pool per request, and replays each attempt with the next key.
- New `Provider.KeyFailoverConfig(logger)` interface method. Anthropic injects `X-Api-Key`; OpenAI injects `Authorization: Bearer ...`; Copilot returns an empty config.
- `passthrough.go` wires `NewKeyFailoverTransport` around the existing apidump middleware, so every retry attempt is recorded.
## Related Issues
Related to: https://github.com/coder/internal/issues/1446
Related to: https://linear.app/codercom/issue/AIGOV-197/aibridge-automatic-key-failover-for-bridged-and-passthrough-routes
## Follow-up PRs
- Remove dead `Provider.InjectAuthHeader` method now that all auth is applied per-attempt by `KeyFailoverTransport`.
- Bedrock multi-key support.
- Refactor provider vs interceptor config separation.
- Record the actually-used key in the interception credential hint after failover.
> [!NOTE]
> Initially generated by Claude Opus 4.7, modified and reviewed by @ssncferreira
This PR merges code from `coder/aibridge` repository into `coder/coder`.
It was split into 4 PRs for easier review but stacked PRs will need to
be merged into this PR so all checks pass.
* https://github.com/coder/coder/pull/24190 -> raw code copy (this PR,
before merging PRs on top of it, it was just 1 commit:
https://github.com/coder/coder/commit/70d33f33200c7e77df910957595715f81f9bec24)
* https://github.com/coder/coder/pull/24570 -> update imports in
`coder/coder` to use copied code
* https://github.com/coder/coder/pull/24586 -> linter fixes and CI
integration (also added README.md)
* https://github.com/coder/coder/pull/24571 -> added exclude to
scripts/check_emdash.sh check
Original PR message (before PR squash):
Moves coder/aibridge code into coder/coder repository.
Omitted files:
- `go.mod`, `go.sum`, `.gitignore`, `.github/workflows/ci.yml,`
`Makefile`, `LICENSE`, `README.md` (modified README.md is added later)
- `.github`, `example`, `buildinfo,` `scripts` directories
Simple verification script (will list omitted files)
```
tmp=$(mktemp -d)
echo "$tmp"
git clone --depth=1 https://github.com/coder/aibridge "$tmp/aibridge"
git clone --depth=1 --branch pb/aibridge-code-move https://github.com/coder/coder "$tmp/coder"
diff -rq --exclude=.git "$tmp/aibridge" "$tmp/coder/aibridge"
# rm -rf "$tmp"
```
Susana Ferreira