Bug Description

Manual session compression (/compress) causes system prompt to double in size (20,957 → 42,303 chars, +102%) due to duplicate agent identity definitions being concatenated.

Steps to Reproduce

1. Run session with 300+ messages

2. Trigger manual compression (/compress)

3. Check database:
   bash
   sqlite3 ~/.hermes/state.db "SELECT id, length(system_prompt) FROM sessions ORDER BY started_at DESC LIMIT 2;"

4. Verify duplication:
   bash
   sqlite3 ~/.hermes/state.db "SELECT system_prompt FROM sessions WHERE id = 'new_session_id';" | grep -c "You are Hermes Agent"
   Returns: 2 (should be 1)

Expected Behavior

Actual Behavior

Affected Component

Other

Messaging Platform (if gateway-related)

No response

Debug Report

Report       https://paste.rs/JoS7X
  agent.log    https://paste.rs/eBZD3
  gateway.log  https://paste.rs/4lssL

Operating System

macOS 26.4.1

Python Version

3.11.15

Hermes Version

v0.11.0 (2026.4.23)

Additional Logs / Traceback (optional)

Root Cause Analysis (optional)

No response

Proposed Fix (optional)

No response

Are you willing to submit a PR for this?

• I'd like to fix this myself and submit a PR