Adds a bund of optimizations to chatdebug:
In `coderd/x/chatd/chatdebug`:
- Adds a benchmark (excluding LLM and database stuff)
- Replaces string concatenation with strings.Builder when accumulating
stream parts (~105,000ns -> ~50,00ns)
- Removes double JSON encode in RecordingTransport (114,000ns ->
64,000ns)
In `coderd/util/strings`:
- Adds a benchmark for Truncate
- Removes unnecessary allocations in Truncate (~110,000ns -> 1,550ns in
truncation case, 1 alloc -> 0 allocs in no truncation case)
> 🤖 Claude helped with this.
> Mux working on behalf of Mike.
Debug recording could consume request bodies when a provider SDK
returned the active body from `GetBody`, which left the upstream request
with an empty body after capture.
Reset the request body after debug capture and add coverage for shared
`GetBody` readers so debug logging does not alter the bytes sent
upstream.
`chat_turn` debug steps persist with `attempts: []` even when the
streaming call to Anthropic completes successfully. Fantasy's
Anthropic SSE adapter iterates the response to EOF via
`for stream.Next()` and abandons the body without calling `Close()`,
so `RecordingTransport`'s Close-only recording path never fires and
the attempt is lost. Non-streaming runs (`quickgen`,
`title_generation`) go through `model.Generate(...)` and are
unaffected.
Record on `io.EOF` for `text/event-stream` bodies specifically.
Non-SSE responses stay on the Close-only path so JSON integrity,
content-length validation, and inner-`Close()` error semantics are
preserved. `record()` is already `sync.Once`-guarded, so a later
`Close()` is a no-op for recording.
Cian Johnston