Feature/idempotent session sync

[Harshit4847]

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[Copilot]

🟡 Changes recommended

Resolve the API contract mismatch and add coverage for partial or empty acknowledgements.

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Pull request overview

This PR adds deterministic client session IDs and acknowledgement handling for idempotent session uploads.

Changes:

• Renames the upload identifier to clientSessionId.
• Marks sessions sent based on accepted server IDs.
• Updates the API DTOs and synchronization tests.

The API response currently conflicts with the documented endpoint contract (critical, 3 votes), and partial or empty acknowledgements lack test coverage (critical, 2 votes).

File summaries

File	Summary
app/src/main/java/com/harshit/crossdevicetracker/SessionUploadMapper.kt	Maps local IDs to client session IDs.
app/src/main/java/com/harshit/crossdevicetracker/SessionUploadDto.kt	Defines the client session ID field.
app/src/main/java/com/harshit/crossdevicetracker/SessionSyncService.kt	Processes accepted sessions; needs partial/empty acknowledgement tests.
app/src/main/java/com/harshit/crossdevicetracker/SessionApi.kt	Uses the acknowledgement response type, which conflicts with the documented endpoint contract.
app/src/main/java/com/harshit/crossdevicetracker/AcceptedTimeLogsResponse.kt	Defines the acknowledgement response model.
app/src/androidTest/java/com/harshit/crossdevicetracker/SessionSyncServiceTest.kt	Updates synchronization tests and fake API responses.

Review details

Suppressed comments (1)

app/src/main/java/com/harshit/crossdevicetracker/SessionSyncService.kt:40

• A 2xx response with no body or an empty acknowledgement is treated as a permanent failure for every session in the batch. markSessionFailed removes records from getPendingSessions() (the query only selects PENDING), so a missing acknowledgement does not leave these sessions retryable even though it does not prove that the server rejected them. Keep them pending and stop/report a protocol error, or only mark sessions failed when the server explicitly identifies rejected IDs.

                    if (acceptedIdSet == null || acceptedPendingCount == 0) {
                        val errMsg = "Successful sync response did not accept any pending session ids"
                        for (session in pendingSessions) {
                            sessionRepository.markSessionFailed(session.id, errMsg)
                        }

• Files reviewed: 6/6 changed files
• Comments generated: 2
• Review effort level: Lite

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