fix(session): make GET /sessions/{id} reflect on-disk archives when counter is stale (#1550)

[yeyitech]

Summary

Closes #1550. Sessions written through async / out-of-band paths (e.g. the Hermes OpenViking provider) materialize archive directories on disk but leave the in-record message_count / commit_count at zero. GET /api/v1/sessions/{id} then read those zeros verbatim, contradicting the on-disk evidence.

The read path now also computes archive_count from the on-disk archive directories. When the persisted counters are zero but archives exist, the derived value is surfaced so the API and CLI no longer report "nothing happened" for sessions that clearly did.

The persisted counters are still authoritative for the regular synchronous write path; this fallback only fires when persisted state is stale relative to disk — so the fix self-heals already-wedged sessions in the wild.

Test plan

• pytest tests/server/test_session_counters.py -x -q passes.
• Manual: reproduce the issue's setup (write archive dirs by hand under a fresh session UUID), call GET /api/v1/sessions/{id} → response reports archive_count > 0.
• Existing tests/server/test_api_sessions.py still passes (no regression on the synchronous path).

Closes #1550

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PR Reviewer Guide 🔍

Here are some key observations to aid the review process:

🎫 Ticket compliance analysis 🔶 1550 - Partially compliant Compliant requirements: GET /sessions/{id} now uses on-disk archive count as fallback when persisted counters are zero Persisted counters remain authoritative for synchronous path Added new archive_count field to response Non-compliant requirements: No fix for the root cause of why counters are not updated in the first place Requires further human verification: Manual reproduction of the original issue setup

⏱️ Estimated effort to review: 2 🔵🔵⚪⚪⚪

🏅 Score: 85

🧪 PR contains tests

🔒 No security concerns identified

✅ No TODO sections

🔀 No multiple PR themes

⚡ Recommended focus areas for review Possible Incorrect Archive Count Archive counting does not verify items are directories. A file named "archive_001.txt" would be incorrectly counted as an archive directory. return sum( 1 for item in items if isinstance(item, dict) and str(item.get("name", "")).startswith("archive_") ) Broad Exception Catch Broad exception catch without logging may hide real filesystem errors. Consider logging the exception at debug level. except Exception: return 0

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