## Problem
Anthropic's API returns a 400 error when `web_search` tool results are
missing:
```
web_search tool use with id srvtoolu_... was found without a corresponding web_search_tool_result block
```
**Root cause:** `persistStep` in `chatd.go` splits ALL
`ToolResultContent` blocks into separate tool-role DB rows.
Provider-executed (PE) tool results like `web_search` must stay in the
assistant message — Anthropic expects `server_tool_use` and
`web_search_tool_result` in the same turn.
The previous fix (#22976) added repair passes to drop PE results during
reconstruction, which fixed cross-step orphans but broke the normal case
(PE result correctly in the same step).
## Fix
Three changes that address the root cause:
1. **`persistStep` (chatd.go):** Check `ProviderExecuted` before
splitting `ToolResultContent` into tool rows. PE results stay in
`assistantBlocks` and are stored in the assistant content column.
2. **`ToMessageParts` (chatprompt.go):** Propagate the
`ProviderExecuted` field to `ToolResultPart` so the fantasy Anthropic
provider can identify PE results and reconstruct the
`web_search_tool_result` block.
3. **Keep existing repair passes** for backward compatibility with
legacy DB data where PE results were incorrectly persisted as separate
tool messages.
## Tests
- `TestProviderExecutedResultInAssistantContent` — PE result stored
inline in assistant content round-trips correctly with
`ProviderExecuted` preserved.
- `TestProviderExecutedResult_LegacyToolRow` — legacy PE results in
tool-role rows are still dropped correctly.
- All existing tests pass (including the 3 PE tests from #22976).
Kyle Carberry
c3923f2ccd