> 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
Explore sub-agents previously could not use `web_search` or external MCP
tools. `runChat` hard-skipped both for Explore. Lifting those guards
naively would over-grant tools, because a child chat could outlive the
spawning turn's plan-mode filter.
This change persists the spawning parent turn's filtered external MCP
server IDs onto the child Explore chat, and simplifies the Explore
provider-tool filter in `runChat`:
- New `resolveExploreToolSnapshot` helper: computes the child's
inherited external MCP subset by running the parent's configs through
`filterExternalMCPConfigsForTurn` (plan-mode policy) and, if the parent
is itself an Explore child, further narrowing to the parent's own
persisted `MCPServerIDs`. The result is written to the child's
`MCPServerIDs` column at spawn time.
- The existing `mcp_server_ids` column is the sole durable snapshot. No
new chat column is added.
- `runChat` for Explore children: loads MCP tools from the persisted
snapshot, and keeps only `web_search` from provider-native tools (to
block computer-use and other write-style tools, since Explore is
read-only). Whether `web_search` is actually available is a per-model
decision, determined by the current model config, just like a main chat.
- Built-in Explore allowlist is unchanged. Workspace-local MCP remains
excluded for Explore.
Verification: `go build ./...`, `go test ./coderd/x/chatd/... -count=1`,
`make gen` (clean tree), `make lint/emdash`, `go vet`. Deep-review ran
12 reviewers on the feature and 5 on the clarity refactor; CAR reviewed
and approved; a subsequent scope reduction dropped a temporary
`allow_web_search` column in favor of per-model handling.
> Mux is acting on Mike's behalf.
- Add `chattest.OpenAI(t)` convenience wrapper around `NewOpenAI` with
sensible defaults (JSON title response for non-streaming, text chunk for
streaming)
- Update `seedChatDependencies` to use it instead of an empty base URL,
preventing title generation from hitting real `api.openai.com` with a
fake key:
```
t.go:111: 2026-04-20 19:23:31.885 [debu] coderd.chatd.processor: title model candidate failed chat_id=edb43454-f23d-4163-9974-d101b8091de6 chat_id=edb43454-f23d-4163-9974-d101b8091de6 ...
error= generate structured title:
github.com/coder/coder/v2/coderd/x/chatd.generateStructuredTitleWithUsage
/home/coder/src/coder/coder/coderd/x/chatd/quickgen.go:443
- unauthorized: Incorrect API key provided: test-api-key. You can find your API key at https://platform.openai.com/account/api-keys.
```
> 🤖
Chat title generation used free-form text completion, which let models
respond conversationally instead of producing a title. Review chats
started with GitHub URLs were especially affected — models would say "I
don't have the ability to browse external links" and that string became
the persisted title.
Replace the raw-text `generateShortText` path with structured output via
`object.Generate[generatedTitle]`. Both auto-title and manual retitle
now go through the same typed contract: the model must return a JSON
object with a `title` field, validated and normalized before
persistence. Invalid outputs (empty, too long) are rejected and retried
through the existing candidate-model fallback loop.
OpenAI Responses follow-up turns were replaying full assistant/tool
history even when `store=true`, which breaks after reasoning +
provider-executed `web_search` output.
This change persists the OpenAI response ID on assistant messages, then
in `coderd/x/chatd` switches `store=true` follow-ups to
`previous_response_id` chaining with a system + new-user-only prompt.
`store=false` and missing-ID cases still fall back to manual replay.
It also updates the fake OpenAI server and integration coverage for the
chaining contract, and carries the rebased path move to `coderd/x/chatd`
plus the migration renumber needed after rebasing onto `main`.
- 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. 🧑💻
Michael Suchacz