LoopObserver omits on_compaction and on_loop_cancelled, which BaseObserver defines and the loop dispatches

[zhanghanduo]

The two observer surfaces disagree. LoopObserver (Protocol, agent_core/loop_types.py:293) stops at on_loop_end; BaseObserver (:326) additionally defines on_compaction (:363) and on_loop_cancelled (:370) — and the loop dispatches both.

Consequences:

• LoopObserver is @runtime_checkable, so isinstance(obs, LoopObserver) passes for an observer with no compaction hook. notify_observers' getattr(obs, method, None) probe then silently drops every compaction record for it — no warning, no log.
• A strict-typed host holding list[LoopObserver] cannot call on_compaction at all, even though the CompactionEvent record and the COMPACTION_SEQ_KEY contract in agent_core/runtime/loop/compact.py are shared and expect a consumer.

Decision needed: if the two hooks are optional, say so in the Protocol docstring so the silent-drop behaviour is intended and documented. If they are contract, declare them on LoopObserver — which makes BaseObserver a conforming default rather than a superset. Related: #4 (the cancellation hook's drain gap).

Provenance: pre-existing in ApodexHarness/miroharness/core/loop_types.py, ported verbatim by #1 — not introduced by the refactor. ApodexHarness carries the same code and needs the same change until it consumes AgentCore.

[zhanghanduo]

Settled on main by 63dba6f (not auto-linked — literal \n\n before the Refs trailer).

Of the two options this issue put up, the first was taken: the two hooks are optional, and that is now documented rather than implicit. LoopObserver's docstring states it (agent_core/loop_types.py:382):

Compaction and cancellation notifications are optional so legacy observers remain valid. Hosts can narrow those hooks with CompactionObserver and CancellationObserver; BaseObserver implements both.

Both consequences the issue raised are addressed:

• The silent-drop behaviour in notify_observers' getattr(obs, method, None) probe is now intended and stated, so a runtime_checkable pass on an observer without a compaction hook is no longer a surprise.
• The strict-typed host is unblocked without widening the required surface: two narrow @runtime_checkable Protocols were added — CompactionObserver (:419) and CancellationObserver (:427) — so a host holding list[LoopObserver] narrows to those to call the hooks, and BaseObserver conforms to both.

Pinned by tests/test_loop_types.py::test_legacy_observer_satisfies_runtime_protocol (:350) and ::test_base_observer_satisfies_optional_hook_protocols (:368).

Related #4 (the cancellation drain gap) is fixed in the same commit.

Downstream: miroharness/core/loop_types.py still carries the undocumented split. Tracking that backport separately.

[zhanghanduo]

Correction to the "Downstream" note above.

That note is accurate for MiroHarness main, which still carries the standalone 790-line copy — but it is already stale for the integration branch. On refactor/agent-core, miroharness/core/loop_types.py is a 75-line compatibility facade that re-exports agent_core.loop_types (done by 1bedcc52 refactor: consume shared runtime contracts), and that branch pins:

apodex-agent-core @ git+ssh://git@github.com/ApodexAI/AgentCore.git@a9b5272d

git merge-base --is-ancestor 63dba6f a9b5272 confirms the pin already contains this fix.

So no backport is needed. The downstream copy is not being patched in parallel; it is being deleted by the extraction. MiroHarness main keeps the old code only until refactor/agent-core lands, and this fix arrives there through the pin rather than through a second edit.

The only product-specific symbol that stays behind in the facade is wall_deadline_remaining_s, which binds miroharness.core.execution_context and is registered as an allowed delta in scripts/contract/manifest.py.