PR #20424: fix(run_agent): call should_compress_preflight() for sub-threshold engines (#20316)

• Repository: NousResearch/hermes-agent
• Author: Beandon13
• State: open | merged: False
• Link: https://github.com/NousResearch/hermes-agent/pull/20424

Description (problem / solution / changelog)

Summary

• run_conversation now consults ContextEngine.should_compress_preflight() when the request is below threshold_tokens, so engines like hermes-lcm can run incremental leaf-chunk compaction (or other deferred maintenance) without waiting for the 75% context fill cutoff.
• Default ContextEngine.should_compress_preflight() still returns False — the built-in ContextCompressor is unaffected.
• Exceptions raised by the engine hook are caught at debug level and treated as "skip preflight", so a buggy plugin can't break an otherwise-healthy turn.

Closes #20316

Testing

• scripts/run_tests.sh tests/run_agent/test_run_agent.py::TestRunConversation::test_engine_preflight_fires_below_threshold tests/run_agent/test_run_agent.py::TestRunConversation::test_engine_preflight_skipped_when_returns_false tests/run_agent/test_run_agent.py::TestRunConversation::test_engine_preflight_exception_does_not_break_turn -q

▶ running pytest with 4 workers, hermetic env, in /tmp/hermes-r2-1-fix
  (TZ=UTC LANG=C.UTF-8 PYTHONHASHSEED=0; all credential env vars unset)
bringing up nodes...
bringing up nodes...

...                                                                      [100%]
3 passed in 4.03s

• scripts/run_tests.sh tests/agent/test_context_engine.py -q

...................                                                      [100%]
19 passed in 1.73s

• scripts/run_tests.sh tests/run_agent/test_run_agent.py::TestRunConversation::test_context_compression_triggered tests/run_agent/test_run_agent.py::TestRunConversation::test_glm_prompt_exceeds_max_length_triggers_compression -q

..                                                                       [100%]
2 passed in 6.34s

Changed files

• run_agent.py (modified, +31/-0)
• tests/run_agent/test_run_agent.py (modified, +136/-0)

PR #15806: fix(run_agent): wire up should_compress_preflight() per-turn ingest hook

• Repository: NousResearch/hermes-agent
• Author: catgodtw
• State: open | merged: False
• Link: https://github.com/NousResearch/hermes-agent/pull/15806

Description (problem / solution / changelog)

ContextEngine.should_compress_preflight() is documented as the per-turn ingest entry for plugin engines, but run_agent.py never calls it. PR #10088 explicitly noted this as dead code when skipping #9675:

#9675 (preflight check) — dead code, run_agent.py never calls should_compress_preflight()

This breaks plugin context engines that rely on the hook for per-turn message ingest. hermes-lcm overrides should_compress_preflight() to persist messages each turn into its DAG store, but with the hook never called, the lossless message store stays empty until compress() fires at the threshold (typically ~96K tokens). Reproducible:

$ hermes chat -q "test" -Q $ sqlite3 ~/.hermes/lcm.db "SELECT COUNT(*) FROM messages;" 0

(Verified on hermes-agent v0.11.0 with hermes-lcm v0.7.0.)

Add two calls to should_compress_preflight(messages):

1. Top of the main loop, right after api_call_count is incremented — per-turn ingest before each API call.
2. End of run_conversation(), before the on_session_end plugin hook — final flush so the last assistant message reaches the engine when the turn exited via the no-tool-calls branch and skipped the per-turn hook above.

The return value is discarded; compression is still decided by the later should_compress(_real_tokens) call which uses the provider- reported token count. Both calls are wrapped in try/except so a misbehaving plugin engine cannot break the conversation loop.

Default ContextEngine.should_compress_preflight() returns False with no work, so this is zero overhead for the built-in ContextCompressor and any engine that does not override the hook.

After this fix: $ hermes chat -q "test" -Q $ sqlite3 ~/.hermes/lcm.db "SELECT COUNT(*) FROM messages;" 2

Refs:

• #9675 (closed: feat(compressor): implement preflight compression check)
• #10088 (merged body: skipped #9675 as dead code)
• stephenschoettler/hermes-lcm#68 (LCM author flagged host integration issue but could not file upstream because GitHub Issues was off on a different fork)

What does this PR do?

Related Issue

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Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 🔒 Security fix
• 📝 Documentation update
• ✅ Tests (adding or improving test coverage)
• ♻️ Refactor (no behavior change)
• 🎯 New skill (bundled or hub)

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Code

• I've read the Contributing Guide
• My commit messages follow Conventional Commits (fix(scope):, feat(scope):, etc.)
• I searched for existing PRs to make sure this isn't a duplicate
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• I've run pytest tests/ -q and all tests pass
• I've added tests for my changes (required for bug fixes, strongly encouraged for features)
• I've tested on my platform: <!-- e.g. Ubuntu 24.04, macOS 15.2, Windows 11 -->

Documentation & Housekeeping

• I've updated relevant documentation (README, docs/, docstrings) — or N/A
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Changed files

• run_agent.py (modified, +29/-0)