We weren't stripping the API base (`/api/v2/aibridge`), leading to 404s
when using the in-memory transport.
Signed-off-by: Danny Kopping <danny@coder.com>
### TL;DR
Introduces an in-process `TransportFactory` for aibridge so that chatd (coder-agent LLM traffic) can route requests through the aibridged handler without crossing the HTTP route or requiring a license entitlement check.
### What changed?
- Added a new `coderd/aibridge` package with a `TransportFactory` interface and a `Source` type for tagging the call site on request contexts. `SourceAgents` is defined as the constant for coder-agent traffic.
- Implemented `NewTransportFactory` in `coderd/aibridged/transport.go`, which returns an `http.RoundTripper` that dispatches requests to the aibridged handler in-process. The response body is streamed through an `io.Pipe` so SSE/NDJSON/chunked responses propagate token-by-token. Handler panics are recovered and surfaced as 500 responses, and context cancellation closes the pipe with the appropriate error.
- `RegisterInMemoryAIBridgedHTTPHandler` now also constructs a `TransportFactory` from the registered handler and stores it on `API.AIBridgeTransportFactory` (an `atomic.Pointer`), making it available to chatd without going through the license-gated HTTP route.
- Added `API.AIBridgeTransportFactory` as a public `atomic.Pointer[aibridge.TransportFactory]` field on `coderd.API`.
### How to test?
- `coderd/aibridged/transport_test.go` covers: transport creation, nil-handler errors, source attachment to context, header/status passthrough, streaming (SSE-style chunked writes visible before handler completion), context cancellation closing the body with an error, concurrent requests, handler panics producing 500s, and handlers that return without writing.
- `coderd/aibridge_test.go` verifies that `AIBridgeTransportFactory` starts as nil on AGPL coderd, can be stored and loaded atomically, and that the stored factory correctly dispatches requests through the stub handler.
### Why make this change?
Chatd needs to send LLM requests through aibridge in-process rather than via the external HTTP route, which is license-gated. The `TransportFactory` abstraction provides a clean seam: the entitlement check remains on the HTTP route for external callers, while in-process coder-agent traffic bypasses it through the factory. The `Source` type allows downstream handlers and logs to attribute traffic without gating behavior on the caller identity.
In order to allow Coder Agents to use AI Gateway in OSS, we need to rehome the `aibridged`\-related code into the AGPL path.
The HTTP API is only registered under enterprise so will still require the AI Governance Add-on to be present in order to use it, whereas Coder Agents uses an in-memory pipe to the same handlers.
Danny Kopping