## Problem
When a chat is interrupted while tools are executing, the step content
(text, reasoning, tool calls, and partial tool results) was being lost.
Two gaps existed:
1. **During tool execution**: `executeTools` returns with error results
for interrupted tools, but the subsequent `PersistStep(ctx, ...)` fails
on the canceled context and returns `ErrInterrupted` without persisting
anything.
2. **PersistStep race**: If the context is canceled between the
post-tool interrupt check and the `PersistStep` call, the same loss
occurs.
This is inconsistent with how we handle stream interruptions (which
properly flush and persist partial content via `persistInterruptedStep`)
and how [coder/blink](https://github.com/coder/blink) handles
interruptions (always inserting the response message regardless of
execution phase).
## Fix
Two changes in `chatloop.go`:
- **Post-tool-execution interrupt check**: After `executeTools` returns,
check if the context was interrupted and route through
`persistInterruptedStep` (which uses `context.WithoutCancel` internally)
to save the accumulated content.
- **PersistStep fallback**: If `PersistStep` returns `ErrInterrupted`,
retry via `persistInterruptedStep` so partial content is not lost.
## Tests
- `TestRun_InterruptedDuringToolExecutionPersistsStep`: Verifies that
when a tool is blocked and the chat is interrupted, the step (text +
reasoning + tool call + tool error result) is persisted via the
interrupt-safe path.
- `TestRun_PersistStepInterruptedFallback`: Verifies that when
`PersistStep` itself returns `ErrInterrupted`, the step is retried via
the fallback path and content is saved.
Kyle Carberry
42c12176a0