Kyle Carberry 2bdacae5f5 feat(chatd): add LLM stream retry with exponential backoff (#22418) ...

## Summary

Adds automatic retry with exponential backoff for transient LLM errors
during chat streaming and title generation. Inspired by
[coder/mux](https://github.com/coder/mux)'s retry mechanism.

## Key Behaviors

- **Infinite retries** with exponential backoff: 1s → 2s → 4s → ... →
60s cap
- **Deterministic delays** (no jitter)
- **Error classification**: retryable (429, 5xx, overloaded, rate limit,
network errors) vs non-retryable (auth, quota, context exceeded, model
not found, canceled)
- **Retry status published to SSE stream** so frontend can show
"Retrying in Xs..." UI
- **Title generation** retries silently (best-effort, nil onRetry
callback)

## New Package: `coderd/chatd/chatretry/`

| File | Purpose |
|------|---------|
| `classify.go` | `IsRetryable(err)` and `StatusCodeRetryable(code)` |
| `backoff.go` | `Delay(attempt)` — exponential doubling with 60s cap |
| `retry.go` | `Retry(ctx, fn, onRetry)` — infinite loop with
context-aware timer |

## Test Helpers: `coderd/chatd/chattest/errors.go`

Anthropic and OpenAI error response builders for use in chattest
providers:
- `AnthropicErrorResponse()`, `AnthropicOverloadedResponse()`,
`AnthropicRateLimitResponse()`
- `OpenAIErrorResponse()`, `OpenAIRateLimitResponse()`,
`OpenAIServerErrorResponse()`

## SDK Changes: `codersdk/chats.go`

- New `ChatStreamEventType: "retry"`
- New `ChatStreamRetry` struct with `Attempt`, `DelayMs`, `Error`,
`RetryingAt` fields
- TypeScript types auto-generated

## Changed Files

- `coderd/chatd/chatloop/chatloop.go` — wraps `agent.Stream()` in
`chatretry.Retry()`
- `coderd/chatd/chatd.go` — publishes retry events to SSE stream with
logging
- `coderd/chatd/title.go` — wraps `model.Generate()` in silent retry
- `coderd/chatd/chattest/anthropic.go` / `openai.go` — error injection
support

## Tests

42 tests covering classification (33), backoff (9), and retry scenarios
(8).

2026-02-27 18:34:33 -05:00

..

chatretry_test.go

feat(chatd): add LLM stream retry with exponential backoff (#22418)

2026-02-27 18:34:33 -05:00

chatretry.go

feat(chatd): add LLM stream retry with exponential backoff (#22418)

2026-02-27 18:34:33 -05:00