**Breaking change for changelog:**
> `codersdk.Chat.last_error` now returns a structured `ChatError` object
(`{message, kind, provider, retryable, status_code, detail}`) instead of
a plain string. The chats API is experimental
(`/api/experimental/chats`), so this ships without a deprecation cycle;
consumers reading `chat.last_error` as a string must update to read
`chat.last_error.message`. SDK/generated TypeScript terminal error
payloads now use the single `ChatError` type; the live stream error
payload type is renamed from `ChatStreamError` to `ChatError`.
Persisted chat errors now carry the same provider-specific detail (kind,
provider, retryable, HTTP status, optional detail) as the live stream,
so refreshing a failed chat rehydrates with the full structured error
instead of a one-line headline.
Existing rows are migrated in place: legacy text errors are wrapped into
`{message, kind: "generic"}` so already-errored chats still render, and
rows with `last_error IS NULL` stay NULL. Internally, persisted fallback
decoding now reuses the existing `chaterror.KindGeneric` constant, with
no JSON value change.
Closes CODAGT-239
- Adds chat-related dbgen generators covering defaults, overrides, and message field mapping.
- Replaces raw single-row chat, message, provider, and model-config setup in tests with dbgen helpers.
- Simplifies chat seed helpers after moving fixture setup into dbgen.
> Generated with [Coder Agents](https://coder.com/agents).
> Worked on by Mux on Mike's behalf.
## Summary
- Disable OpenAI Responses `previous_response_id` chain mode when the
prior assistant response has unresolved local tool calls, so the next
request can include paired tool outputs instead of sending an incomplete
continuation.
- Update the fantasy pin to a Responses replay fix that preserves stored
reasoning references, only replays web search references when paired
with reasoning, and validates local function-call output pairing before
send.
- Add fake OpenAI Responses input validation for the two production 400
shapes and integration coverage for full-history reasoning plus web
search replay.
- Add sanitized diagnostics for the OpenAI Responses continuity errors.
## Tests
- `go test ./providers/openai -run
'TestResponsesToPrompt_(ReasoningWithStore|ReasoningWithWebSearchCombined|WebSearchRequiresReasoningReference|ReasoningWithFunctionCallCombined|WebSearchProviderExecutedToolResults)|TestPrepareParams_(SkipsProviderExecutedToolReferences|ValidatesFunctionCallOutputPairing)|TestValidateResponsesInput_WebSearchReferenceRequiresReasoning'
-count=1`
- `go test ./providers/openai -count=1`
- `GOWORK=off go test ./coderd/x/chatd/chattest -run
TestValidateResponsesAPIInput -count=1`
- `GOWORK=off go test ./coderd/x/chatd -run
'TestOpenAIResponses(NoStaleWebSearchReplay|FullReplayPairsReasoningAndWebSearch|ChainModeSkipsWhenLocalCallPending|ChainModeStillFiresForProviderExecutedOnly)$|TestResolveChainMode_'
-count=1`
- `GOWORK=off go test ./coderd/x/chatd/chatprompt -run
'TestInjectMissingToolResults_' -count=1`
- `GOWORK=off go test ./coderd/x/chatd/chaterror -run
TestClassify_OpenAIResponsesAPIDiagnostics -count=1`
- `GOWORK=off go test ./coderd/x/chatd/... -count=1`
- `git diff --check`
- `git commit` pre-commit hook
Michael Suchacz