Stephen just confirmed on X that hermes-lcm should be treated as the standalone deliverable/plugin:

• install hermes-lcm
• set the context engine to lcm
• no Hermes core bundling needed

Given that, I think the right framing for this PR is:

• not a prerequisite for hermes-lcm to exist or be usable
• but a Hermes-side host/plugin ergonomics + robustness improvement for external context-engine plugins

So from my side, this PR is still intended as host-support cleanup:

• plugin discovery/init path
• lifecycle handling across /new, /resume, and /branch
• backward-compatible compression hook behavior
• surfacing installed plugin-registered engines more cleanly in Hermes

In other words: hermes-lcm stands on its own, and this PR is about making Hermes a cleaner/more reliable host for external context-engine plugins when people do use them.

@stephenschoettler @teknium1

Pulled one more small host-support commit into this PR.

What it adds

• richer session-boundary hook context for external plugins on /new / reset-style boundaries
• on_session_finalize can now receive:
  • old_session_id
  • previous_messages
  • previous_message_count
• on_session_reset can now receive:
  • old_session_id
  • new_session_id
  • carry_over_context

Why
This keeps Hermes' normal built-in behavior unchanged, but makes Hermes a nicer host for external context-engine plugins that need to handle rollover boundaries safely.

In particular, it helps close the gap we hit while working on external hermes-lcm lifecycle handling: plugins could already see the session boundary, but they did not have enough context to finalize old-session state cleanly.

Validation

• python -m pytest tests/cli/test_session_boundary_hooks.py tests/gateway/test_session_boundary_hooks.py -q
• python -m pytest tests/run_agent/test_context_engine_plugin_init.py tests/run_agent/test_session_reset_fix.py tests/cli/test_cli_new_session.py tests/hermes_cli/test_plugins_cmd.py tests/agent/test_context_engine.py tests/cli/test_session_boundary_hooks.py tests/gateway/test_session_boundary_hooks.py -q

Tagging for visibility: @stephenschoettler @teknium1

Quick correction: I accidentally left vendored repo-shipped LCM files in this branch. That's now removed.

Current scope is back to generic host support only:

• external context engine plugin init/fallback improvements
• session-boundary hook context improvements for plugins

No bundled plugins/context_engine/lcm payload remains in this PR.

Validation rerun after cleanup:

• python -m pytest tests/run_agent/test_context_engine_plugin_init.py tests/run_agent/test_session_reset_fix.py tests/cli/test_session_boundary_hooks.py tests/gateway/test_session_boundary_hooks.py tests/hermes_cli/test_plugins_cmd.py tests/cli/test_cli_new_session.py -q
• 83 passed

Sorry for the noise. @stephenschoettler @teknium1

Rebased this cleanly onto current main and kept the scope strictly generic host support for external context-engine plugins.

What stayed true after the rewrite:

• no vendored hermes-lcm or other plugin implementation under plugins/context_engine/*
• only host-side lifecycle/discovery/compatibility changes remain in the diff
• the PR is mergeable again; GitHub is currently recalculating checks/state on the refreshed head

Local validation on the rewritten branch:

• python -m pytest tests/run_agent/test_context_engine_plugin_init.py tests/run_agent/test_session_reset_fix.py tests/cli/test_session_boundary_hooks.py tests/gateway/test_session_boundary_hooks.py tests/hermes_cli/test_plugins_cmd.py tests/cli/test_cli_new_session.py tests/agent/test_context_engine.py -q
  • 102 passed

Follow-up pushed to this PR to close the biggest remaining host-side session-boundary gaps.

What changed in this extension:

• compression-driven session splits now go through the same context-engine lifecycle seam instead of rotating session_id silently
• background process notifications now carry the logical Hermes conversation session id they were created under
• the gateway drops stale watch/completion notifications after /new or /reset instead of injecting them into the fresh session
• CLI /new no longer waits on the old-session memory flush before the fresh session becomes visible; the flush/commit work is dispatched in the background

Why this helps:

• external context engines no longer see /new//resume//branch as one contract and compression rollover as a different contract
• a fresh session is less likely to feel "sticky" or "half alive" because old background-process follow-up events are fenced at the session boundary
• /new feels more immediate in CLI because old-session cleanup is no longer on the critical path

Validation run on the updated branch:

• pytest tests/run_agent/test_context_engine_plugin_init.py tests/run_agent/test_session_reset_fix.py tests/cli/test_cli_new_session.py tests/hermes_cli/test_plugins_cmd.py tests/agent/test_context_engine.py tests/cli/test_session_boundary_hooks.py tests/gateway/test_session_boundary_hooks.py tests/gateway/test_background_process_notifications.py tests/tools/test_process_registry.py tests/tools/test_notify_on_complete.py tests/tools/test_watch_patterns.py -q
• result: 215 passed

This PR could not be reopened because its original head repository disappeared. Recreated as replacement PR #13370: #13370