fix(handoff): set mode and repositoryId together on cloud hand off

[jonathanlab]

The cloud to local handoff saga only set workspace.mode to "local" but left repositoryId null, which broke everything.

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Created with PostHog Code

[greptile-apps]

Prompt To Fix All With AI

Fix the following 2 code review issues. Work through them one at a time, proposing concise fixes.

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### Issue 1 of 2
apps/code/src/main/services/handoff/service.test.ts:89-90
**`workspaceRepo` mock incomplete for new execute path**

`attachWorkspaceToFolder` calls `this.workspaceRepo.findByTaskId(taskId)` and `this.workspaceRepo.setModeAndRepository(...)`, but the mock here only provides `updateMode`. Any test that exercises `service.execute()` will throw `"workspaceRepo.findByTaskId is not a function"` rather than a clear test failure. Worth extending the mock now so future execute-path tests don't silently regress.

### Issue 2 of 2
apps/code/src/main/services/handoff/handoff-saga.ts:127-137
**Mutable closure variable for revert leaks state across async boundary**

`attachmentRevert` is captured in a mutable outer variable and assigned inside the `execute` callback. The saga framework guarantees `execute` runs before `rollback`, so this is safe today, but it's a fragile pattern — if the step API ever changes or a parallel step is introduced, the rollback could silently call `null?.()` instead of the real revert. Returning the revert through the saga step's output type, if the framework supports it, would be cleaner.

_{Reviews (1): Last reviewed commit: "fix(handoff): set mode and repositoryId ..." | Re-trigger Greptile}