fix(transfer): trust axon upload s3 key

[shark0F0497]

Summary

This PR changes the upload_complete handler to trust the s3_key provided by axon in the WebSocket message, instead of reconstructing it from factory ID, device ID, date, and task ID.

Motivation

Previously, onUploadComplete computed the MCAP S3 key using a hardcoded pattern ({factory}/{device}/{date}/{taskID}.mcap). If axon uploaded the file to a different path (e.g., a different key prefix or naming convention), the ACK verification would fail with a "file not found" error, causing the upload to be stuck in an unacknowledged state. By trusting the s3_key that axon reports in the upload_complete payload, keystone always looks for the exact file that was actually uploaded.

Changes

Modified Files

• internal/api/handlers/transfer.go — Replaced the hardcoded S3 key construction with two new helper functions:

  • uploadCompleteS3Key() — extracts the s3_key field from the WebSocket message payload.
  • uploadCompleteSidecarS3Key() — derives the sidecar JSON key by replacing the .mcap suffix with .json, with a safety check that the MCAP key actually ends in .mcap.

  When s3_key is missing or invalid, the handler logs a warning and skips the ACK flow gracefully (no crash, no retry loop).

Type of Change

• Bug fix (non-breaking change that fixes an issue)

Impact Analysis

Breaking Changes

None

Backward Compatibility

Fully backward compatible — axon already includes s3_key in the upload_complete message payload.