Removes the backend and frontend logic that extracted compact titles
from reasoning/thinking blocks. The `Title` field on `ChatMessagePart`
remains for other part types (e.g. source), but reasoning blocks no
longer have titles derived from first-line markdown bold text or
provider metadata summaries.
**Backend:**
- Remove `ReasoningTitleFromFirstLine`, `reasoningTitleFromContent`,
`reasoningSummaryTitle`, `compactReasoningSummaryTitle`, and
`reasoningSummaryHeadline` from chatprompt
- Simplify `marshalContentBlock` to plain `json.Marshal` (no title
injection)
- Remove title tracking maps and `setReasoningTitleFromText` from
chatloop stream processing
- Remove `reasoningStoredTitle` from db2sdk
- Remove related tests from db2sdk_test
**Frontend:**
- Remove `mergeThinkingTitles` from blockUtils
- Simplify `appendTextBlock` to always merge consecutive thinking blocks
- Remove `applyStreamThinkingTitle` from streamState
- Simplify reasoning/thinking stream handler to ignore title-only parts
- Update tests accordingly
Net: **-487 lines / +42 lines**
Split from #22693 per review feedback.
Fixes multiple bugs in coderd/chatd and sub-packages including race
conditions, transaction safety, stream buffer bounds, retry limits, and
enterprise relay improvements.
See commit message for full list.
## Problem
Three bugs with chat summarization (compaction) share a single root
cause: `ReloadMessages` was never wired up in the production
`chatloop.Run()` call.
### Bug 1: Compaction never fires between steps
The inline compaction guard in `chatloop.go` requires both `Compaction`
and `ReloadMessages` to be non-nil:
```go
if opts.Compaction != nil && opts.ReloadMessages != nil {
```
Since `ReloadMessages` was only set in tests, inline compaction was
**dead code in production**. Long multi-step turns could blow through
the context window.
### Bug 2: Compaction only occurs at end of turn
The post-run safety net doesn't check `ReloadMessages`, so it was the
only compaction path that fired:
```go
if !alreadyCompacted && opts.Compaction != nil { // no ReloadMessages check
```
This meant compaction only happened once, after the entire agent turn
finished.
### Bug 3: Agent stops after summarization
After post-run compaction, `Run()` unconditionally returned `nil`.
`processChat` then set the chat status to `waiting` (done). The agent
never had a chance to continue with its fresh summarized context.
## Fix
1. **Wire up `ReloadMessages`** in `chatd.go`: reloads persisted
messages from the database and re-applies system prompts (subagent
instruction, workspace AGENTS.md).
2. **Wrap the step loop in an outer compaction loop**: when compaction
fires on the model's final step (`compactedOnFinalStep`), reload
messages and `continue` the outer loop so the agent re-enters with
summarized context.
3. **Track `compactedOnFinalStep`** to distinguish inline compaction on
the last step (needs re-entry) from inline compaction mid-loop followed
by more tool-call steps (agent already consumed the compacted context,
no re-entry needed).
4. **Add `maxCompactionRetries = 3`** to prevent infinite compaction
loops.
## Testing
- All 7 existing compaction tests pass unchanged.
- Added `PostRunCompactionReEntersStepLoop` test: verifies that when a
text-only response triggers compaction, the outer loop re-enters and the
agent makes a second stream call with fresh context.
Kyle Carberry