Close local transcription sessions on completion

[kodjima33]

Summary

• mark local transcription rows as fully completed after successful upload
• set conversationStatus to completed and fill finishedAt when missing
• keep backend sync fields unchanged

Fixes #6955

Verification

• Mac mini: cd ~/projects/omi/desktop/Desktop && swift build 2>&1 | tail -5
• Build complete on Mac mini

[greptile-apps]

Greptile Summary

This PR fixes locally-originated transcription sessions that were left with a stale conversationStatus of .inProgress and a potentially-null finishedAt after a successful backend upload. The change is confined to markSessionCompleted and touches only three fields on the session record.

• Sets conversationStatus = .completed after upload succeeds, replacing the previous .inProgress default that was never updated on the upload path.
• Fills finishedAt with a ?? coalesce guard so sessions that never received a finishSession call (crash-recovery path) get a non-nil timestamp.
• Captures a single completedAt = Date() value and reuses it for both fields, ensuring finishedAt (fallback) and updatedAt share the same instant.

Confidence Score: 4/5

Safe to merge; the change correctly closes out the local record after a successful upload, and the only imprecision is limited to the crash-recovery fallback path.

The happy path (where finishSession was called before markSessionCompleted) is unambiguously correct. The sole rough edge is the crash-recovery fallback: when finishedAt is nil, the coalesce assigns the upload-completion timestamp rather than actual recording-end time, causing durationSeconds to over-report. This is a minor accuracy concern on an already-degraded code path and does not affect data integrity or backend sync.

desktop/Desktop/Sources/Rewind/Core/TranscriptionStorage.swift — specifically markSessionCompleted and how finishedAt interacts with TranscriptionSessionWithSegments.durationSeconds in crash-recovery scenarios.

Important Files Changed

Filename	Overview
desktop/Desktop/Sources/Rewind/Core/TranscriptionStorage.swift	Adds conversationStatus = .completed and a finishedAt fallback to markSessionCompleted; normal-flow is correct, but crash-recovery path sets finishedAt to upload time rather than recording-end time, potentially inflating durationSeconds

_{Reviews (1): Last reviewed commit: "Close local transcription sessions on co..." | Re-trigger Greptile}

[greptile-apps]

In the crash-recovery fallback, finishedAt is set to completedAt — the moment the upload finished — rather than when recording actually stopped. TranscriptionSessionWithSegments.durationSeconds subtracts startedAt from finishedAt, so for any session recovered without a prior finishSession call (e.g. the app crashed mid-recording), the reported duration will include dead time between the crash and the eventual retry. Keeping nil preserves the nil-safe guard in durationSeconds instead of silently inflating it. If you do want a non-nil value for UI purposes, documenting the approximation in a comment would help future readers.

Suggested change

	let completedAt = Date()
	record.status = .completed
	record.conversationStatus = .completed
	record.finishedAt = record.finishedAt ?? completedAt
	let completedAt = Date()
	record.status = .completed
	record.conversationStatus = .completed
	// Note: finishedAt should have been set by finishSession; if nil (crash-recovery path),
	// we fall back to the upload completion time, which over-estimates recording duration.
	record.finishedAt = record.finishedAt ?? completedAt