Closes CODAGT-541.
## Problem
An Agents chat stream could die with a terminal `context cancelled`
error and surface to the user as a permanent chat failure, even when no
context in our process had actually been canceled. The cancellation was
a provider-returned error value (HTTP/2 RST_STREAM mid-body surfacing as
`context.Canceled` from Go's net/http2), not a real caller cancel.
The chain that produced the bug:
- fantasy passed the provider's `context.Canceled` through unchanged.
- `chaterror.Classify` short-circuited any `errors.Is(err,
context.Canceled)` (or `"context canceled"` text) as terminal generic,
before checking HTTP status codes or other retry signals.
- `chatretry.Retry` did not retry.
- The frontend rendered `type:"error"` and the chat was dead.
The same short-circuit also masked retryable 5xx responses whose
underlying transport error happened to wrap `context.Canceled`.
## Approach
`context.Canceled` has no inherent intent. The same error value can mean
a user pressing Stop, a server shutdown, the silence guard firing, or a
provider-side stream reset. The only layer that can disambiguate is the
one holding both the returned error and the caller context. That is
`chatretry`.
This PR centralizes the policy there and keeps `chaterror` context-free.
## Changes
`coderd/x/chatd/chaterror/classify.go`
- Add `ErrProviderTransportReset` sentinel to explicitly mark
provider-side stream cancellations.
- Remove the broad `context.Canceled` / `"context canceled"`
short-circuit so status codes and other retry signals can win.
- Classify `ErrProviderTransportReset` (with no status code) as a
retryable timeout.
- Keep a fallback that classifies bare `context.Canceled` as
terminal-generic when no other signal is present, so legitimate caller
cancels still terminate cleanly.
`coderd/x/chatd/chatretry/chatretry.go`
- Add `contextError(ctx)` that returns `context.Cause(ctx)` when set,
falling back to `ctx.Err()`, so caller-owned cancel causes
(`ErrInterrupted`, `errStreamSilenceTimeout`, server shutdown sentinels)
propagate cleanly out of the retry loop.
- Add `classifyProviderAttemptError(err)` that wraps a bare
`context.Canceled` in `ErrProviderTransportReset` and reclassifies.
Errors that already classify as retryable or carry a status code are
left alone.
- Restructure `Retry` so the policy is explicit and readable: check
caller cancellation before attempting, run the attempt, check caller
cancellation again before normalizing the provider error, then classify
and retry.
## End-to-end behavior
- Provider returns `context.Canceled` while caller context is healthy:
classified as a retryable timeout, retried, the user sees a brief
`type:"retry"` event and the chat continues.
- User presses Stop: `contextError(ctx)` returns `ErrInterrupted`. Retry
stops. `chatloop` flushes partial content and persists.
- Stream-silence guard fires: `attemptCtx` is canceled with
`errStreamSilenceTimeout`, `guardedStream` produces a classified
retryable error, retry proceeds normally on the still-alive parent.
- Server shutdown: parent context's cause propagates out, retry stops.
coder/fantasy now fails closed when Anthropic or OpenAI Responses
streams close before their provider terminal events instead of yielding
a successful finish.
This bumps the fantasy replacement to coder/fantasy#33 and teaches chat
error classification to treat those failures as retryable timeout errors
with explicit stream-closed messages.
<img width="875" height="311" alt="image"
src="https://github.com/user-attachments/assets/69c6f7b5-c885-46d2-a88b-b7a2b111bd55"
/>
Modifies chatloop error classification behaviour to treat the following as retryable:
* HTTP/2 `force closed`
* GOAWAY
* use of closed network connection
* Modfies user-facing retry banner to show "<provider> is temporarily
unavailable."
Relates to CODAGT-212.
> 🤖
> **PR Stack**
> 1. **#23351** ← `#23282` *(you are here)*
> 2. #23282 ← `#23275`
> 3. #23275 ← `#23349`
> 4. #23349 ← `main`
---
## Summary
`chatretry.Retry()` used pure exponential backoff (1 s, 2 s, 4 s, …) and
never consulted provider `Retry-After` headers. Fantasy's
`ProviderError` carries `ResponseHeaders` including `Retry-After`, but
`chaterror.Classify()` only parsed error text and silently dropped the
structured transport metadata.
This makes `Retry-After` a first-class signal in the classification →
retry pipeline.
<img width="853" height="346" alt="image"
src="https://github.com/user-attachments/assets/65f012b6-8173-43d2-957e-ab9faddea525"
/>
## Changes
### `coderd/chatd/chaterror/classify.go`
- Added `RetryAfter time.Duration` field to `ClassifiedError` — a
normalized minimum retry delay derived from provider response metadata.
- `Classify()` now calls `extractProviderErrorDetails()` before falling
back to text heuristics. Structured `ProviderError.StatusCode` takes
priority over regex extraction.
- `normalizeClassification()` preserves and clamps `RetryAfter`.
### `coderd/chatd/chaterror/provider_error.go` (new)
Provider-specific extraction, isolated from the text-based
classification logic:
- `extractProviderErrorDetails()` unwraps `*fantasy.ProviderError` from
the error chain via `errors.As`.
- `retryAfterFromHeaders()` parses headers in priority order:
1. `retry-after-ms` (OpenAI-specific, millisecond precision)
2. `retry-after` (standard HTTP — integer seconds or HTTP-date)
- Case-insensitive header key lookup.
### `coderd/chatd/chatretry/chatretry.go`
- `effectiveDelay(attempt, classified)` computes `max(Delay(attempt),
classified.RetryAfter)` — the provider hint acts as a floor without
weakening the local exponential backoff.
- `Retry()` now uses `effectiveDelay` and passes the effective delay to
both `onRetry(...)` and the sleep timer, so downstream payloads, logs,
and the frontend countdown stay aligned automatically.
### Tests
- `classify_test.go`: Structured provider status + `Retry-After`
extraction, `retry-after-ms` priority, HTTP-date parsing, invalid header
fallback, `WithProvider` preservation.
- `chatretry_test.go`: Retry-after-as-floor semantics — longer hint
wins, shorter hint keeps base delay.
## Design notes
- **No SDK/API/frontend changes needed.** `codersdk.ChatStreamRetry`
already carries `DelayMs` and `RetryingAt`, and the frontend already
consumes them. The fix is purely in the server-side delay computation.
- **Existing retryability rules unchanged.** This fixes *when* we sleep,
not *whether* an error is retryable.
- **Provider hint is a floor:** `max(baseDelay, RetryAfter)` ensures we
never retry earlier than the provider asks, and never weaken our own
backoff curve.
> **PR Stack**
> 1. #23351 ← `#23282`
> 2. #23282 ← `#23275`
> 3. **#23275** ← `#23349` *(you are here)*
> 4. #23349 ← `main`
---
## Summary
Extracts a structured error classification subsystem for agent chat
(`chatd`) so that retry and error payloads carry machine-readable
metadata — error kind, provider name, HTTP status code, and retryability
— instead of raw error strings.
This is the **backend half** of the error-handling work. The frontend
counterpart is in #23282.
## Changes
### New package: `coderd/chatd/chaterror/`
Canonical error classification — extracts error kind, provider, status
code, and user-facing message from raw provider errors. One source of
truth that drives both retry policy and stream payloads.
- **`kind.go`**: Error kind enum (`rate_limit`, `timeout`, `auth`,
`config`, `overloaded`, `unknown`).
- **`signals.go`**: Signal extraction — parses provider name, HTTP
status code, and retryability from error strings and wrapped types.
- **`classify.go`**: Classification logic — maps extracted signals to an
error kind.
- **`message.go`**: User-facing message templates keyed by kind +
signals.
- **`payload.go`**: Projectors that build `ChatStreamError` and
`ChatStreamRetry` payloads from a classified error.
### Modified
- **`codersdk/chats.go`**: Added `Kind`, `Provider`, `Retryable`,
`StatusCode` fields to `ChatStreamError` and `ChatStreamRetry`.
- **`coderd/chatd/chatretry/`**: Thinned to retry-policy only;
classification logic moved to `chaterror`.
- **`coderd/chatd/chatloop/`**: Added per-attempt first-chunk timeout
(60 s) via `guardedStream` wrapper — produces retryable
`startup_timeout` errors instead of hanging forever.
- **`coderd/chatd/chatd.go`**: Publishes normalized retry/error payloads
via `chaterror` projectors.
- Moves `coderd/chatd/`, `coderd/gitsync/`, `enterprise/coderd/chatd/`
under `x/` parent directories to signal instability
- Adds `Experimental:` glue code comments in `coderd/coderd.go`
> 🤖 This PR was created with the help of Coder Agents, and was
reviewed by my human. 🧑💻
Hugo Dutka