merge_interventions lets an empty-string stop_reason shadow a later real one

[zhanghanduo]

agent_core/loop_types.py merges stop reasons with a None check:

if stop_reason is None and iv.stop_reason is not None:
    stop_reason = iv.stop_reason

Intervention.stop_reason is str | None, so an observer returning Intervention(stop_reason="") — e.g. a reason built from a config value that defaulted empty — claims the slot.

Consequence: a later observer's real stop_reason="budget_exhausted" is discarded, and a loop testing truthiness (if merged.stop_reason:) then sees no stop at all — the run continues past both stop requests. A budget or deadline observer silently stops working.

Fix direction: treat the empty string as absent — normalise "" to None at merge, or gate on truthiness. The docstring rule ("first non-None wins") should be restated as "first non-empty wins". Worth a test in tests/test_loop_types.py pinning the shadowing case.

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]

Fixed on main by 63dba6f (not auto-linked — that commit's Refs trailer sits after a literal \n\n).

merge_interventions now gates on truthiness, so "" is treated as absent (agent_core/loop_types.py:606):

if stop_reason is None and iv.stop_reason:
    stop_reason = iv.stop_reason

The docstring rule was restated as the issue asked — "take the first non-empty stop". The shadowing case is pinned by tests/test_loop_types.py::test_empty_stop_reason_does_not_shadow_later_reason (:110), alongside test_stop_reason_first_non_none_wins (:99) so neither direction can regress silently.

Downstream: miroharness/core/loop_types.py:777 still has the is not None form. 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.