Condenses the substance of PRs #16453, #17453, #16451, #17600, and #13373
into a minimal generic host contract that external context engine plugins
(e.g. hermes-lcm) need to integrate cleanly. Drops scaffolding that
duplicated existing infrastructure or had marginal value.
Five concrete changes:
1. `_transition_context_engine_session()` on AIAgent — generic lifecycle
helper that fires on_session_end → on_session_reset → on_session_start
→ optional carry_over_new_session_context. Engines implement only the
hooks they need; missing hooks are skipped. Built-in compressor keeps
its existing reset-only behavior because callers default to no
metadata. `reset_session_state()` now optionally accepts
previous_messages / old_session_id / carry_over_context and delegates
to the transition helper when provided. (#16453)
2. `conversation_id` passed to `on_session_start()` — both the
agent-init call site and the compression-boundary call site now
forward `self._gateway_session_key` so plugin engines have a stable
conversation identity that survives session_id rotation (compression
splits, /new, resume). The key already existed on AIAgent; it just
wasn't reaching engines. (#16453)
3. Canonical cache buckets forwarded to engines — the usage dict passed
to `update_from_response()` now includes input_tokens, output_tokens,
cache_read_tokens, cache_write_tokens, and reasoning_tokens on top of
the legacy prompt/completion/total keys. Engines can make decisions on
cache-hit ratios and reasoning costs instead of only aggregates. ABC
docstring updated. (#17453)
4. Plugin-registered context engines visible in the picker —
`_discover_context_engines()` in plugins_cmd.py now also includes
engines registered via `ctx.register_context_engine()` from plugin
manifests, deduplicating by name so repo-shipped descriptions win on
collision. (#16451)
5. `_EngineCollector.register_command()` — context engines using the
standard `register(ctx)` pattern can now expose slash commands (e.g.
`/lcm`). Routes to the global plugin command registry with the same
conflict-rejection policy regular plugins use (no shadowing built-ins,
no clobbering other plugins). Previously these calls hit a no-op and
the slash commands silently never appeared. (#17600)
Dropped from the original 5 PRs:
- Compression boundary signal (`boundary_reason="compression"`) from
#16453 — already on main at `agent/conversation_compression.py:412-424`,
landed via the bg-review extraction.
- `discover_plugins()` before fallback in run_agent.py from #16451 —
redundant: `get_plugin_context_engine()` already routes through
`_ensure_plugins_discovered()` which is idempotent.
- Runtime identity diagnostics method + helpers from #13373 (+251 LOC) —
operators can already read engine state via `engine.get_status()`;
the diagnostics view added marginal value relative to its surface area.
- The 553-LOC slash-command machinery from #17600 — replaced with a
20-LOC `register_command` method on the collector that reuses the
existing plugin command registry instead of building a parallel one.
Net: ~215 LOC of host-contract changes + 282 LOC of focused tests, vs
~1,176 LOC across the original 5 PRs.
Co-authored-by: Tosko4 <1294707+Tosko4@users.noreply.github.com>
Closes#16453.
Closes#17453.
Closes#16451.
Closes#17600.
Closes#13373.
Related: stephenschoettler/hermes-lcm#68.
`AIAgent.__init__` was eagerly calling
`_check_compression_model_feasibility()` which probes the auxiliary
provider chain and runs `get_model_context_length()` (potentially
network-bound) to decide whether the configured auxiliary model can
fit a full compression-threshold window. That cost ~440ms cold on
every agent construction.
Most `chat -q` invocations finish in 1-5 seconds and never accumulate
enough context to trip the compression threshold, so the feasibility
check is pure overhead. The result is also only consumed when
compression actually fires (the function adjusts the live threshold
downward if the aux model can't fit; absent that mutation, the gate
in `conversation_loop.py:442` would never fire anyway).
Defer to first `compress_context()` call via
`agent._compression_feasibility_checked` sentinel. Runs at most once
per agent lifetime, just before the first compression pass. The
warning storage (`_compression_warning`) and gateway replay
machinery is unchanged — it still emits to status_callback on the
first turn that actually needs compression.
E2E timing (chat -q 'hi', 3 runs each):
BEFORE AFTER delta
median wall 2.03s 1.86s -8% (-169ms)
min wall 1.92s 1.63s -15% (-293ms)
Real cold-start observation (synthetic 31-turn agent loop): identical
behavior since feasibility check fires once on first compression and
caches. No semantic difference for sessions that DO compress.
UX trade-off: users with broken auxiliary-provider config no longer
see the warning at session start. They see it when compression first
fires — which is exactly when it matters. For users with working
config (the vast majority), the warning never fires anyway, so the
deferral is invisible.
Tests:
- tests/run_agent/test_compression_feasibility.py — 16/16 pass
(the one test that asserted call-at-init was updated to drive the
lazy check explicitly via agent._check_compression_model_feasibility())
- Live tmux session: 2-turn conversation + tool call completes clean,
zero errors in agent.log
When auxiliary compression's summary generation returns None (aux model
errored, returned non-JSON, timed out, etc.) the compressor previously
still dropped every middle message between compress_start..compress_end
and replaced them with a static 'Summary generation was unavailable'
placeholder. The session kept going but the user silently lost N turns
of context for nothing.
New behavior: on summary failure, compress() aborts entirely — returns
the input messages unchanged and sets _last_compress_aborted=True. The
existing _summary_failure_cooldown_until gate (30-60s) keeps the aux
model from being burned on every turn. Auto-compress callers detect
the no-op (len(after) == len(before)) and stop looping. The chat is
'frozen' at its current size until the next /compress or /new.
Manual /compress (CLI + gateway) now passes force=True which clears
the cooldown so users can retry immediately after an auto-abort. If
the manual retry also fails, the user gets a visible warning telling
them nothing was dropped and how to retry.
- agent/context_compressor.py: compress() gains force= kwarg; failure
branch sets _last_compress_aborted and returns messages unchanged
instead of inserting placeholder.
- run_agent.py: _compress_context() detects abort, surfaces warning,
skips session-rotation entirely, returns messages unchanged.
- cli.py + gateway/run.py: manual /compress paths pass force=True.
- gateway/run.py: hygiene + /compress handlers detect _last_compress_aborted
and emit the new 'Compression aborted' warning (gateway.compress.aborted)
instead of the old 'N historical messages were removed' message.
- locales/*.yaml: new gateway.compress.aborted key in all 16 locales.
- tests: updated to assert the abort contract (messages preserved,
compression_count not incremented, abort flag set, no placeholder
leaked). New test_force_true_bypasses_failure_cooldown covers the
manual-retry path.
Original commit 97a32afdc by helix4u targeted _check_compression_model_feasibility
in pre-refactor run_agent.py. The function body now lives in
agent/conversation_compression.py — re-applied the configured-but-unavailable
provider message there.
Co-authored-by: helix4u <4317663+helix4u@users.noreply.github.com>
