Raise the invariants that were only asserted

[dovvnloading]

Problem

python -O and PYTHONOPTIMIZE=1 strip assert statements entirely, taking whatever they guarded with them — silently, with no error and no log. Seven shipped modules enforced real invariants that way.

Two of them were the event bus's duplicate-registration guards:

assert name not in self._topics,  f"topic {name!r} registered twice"
assert key  not in self._intents, f"intent {topic}/{intent} registered twice"

backend/app.py's _configure_session registers 12 topics and roughly 90 intents in an order its own comments describe as load-bearing. Under -O a duplicate registration silently replaces the previous handler — exactly the failure those checks exist to make loud, made silent by an interpreter flag.

Two more guarded a subprocess pipe against None in the MCP and plugin-worker read loops, where the alternative to the assert is an AttributeError surfacing deep inside a reader thread with no hint that the process was simply never connected.

Nothing in this repo runs under -O today. That is the point: it is cheap to keep true and expensive to discover is not.

Change

All seven become explicit raises — ValueError for a duplicate or malformed registration, TypeError for a non-dataclass args_schema, RuntimeError for a read loop started before its process connected — and a gate pins it.

Two existing tests were asserting the mechanism rather than the invariant (pytest.raises(AssertionError)) and now name the real exception types. That they existed at all is why this was a small change.

Test plan

• tests/test_no_production_asserts.py: AST scan of all four shipped packages plus the loose root modules, with a guards-the-guard check so a wrong root cannot make it pass over an empty file list. Grep would not do here — backend/events.py has the word "assert" inside a docstring, which is why this is AST-based like test_domain_purity.py and test_node_state_migration.py.
• Full suite: 3202 passed, 19 skipped. ruff clean, mypy clean (events.py is inside the mypy scope).

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