[eric] agents: the prefix mode is a type, so the ratchet's own assignment typechecks

backend/apps/agents/manager/run/RunOptions.py

@@ -8,7 +8,7 @@ import json
 import logging
 import time
 import os
-from typing import Dict, List, Optional, Union
+from typing import Dict, List, Literal, Optional, Union
 from typeguard import typechecked
 
 from backend.apps.agents.core.models import AgentSession
@@ -44,17 +44,22 @@ from backend.apps.agents.manager.AgentManagerProtocol import AgentManagerProtoco
 # ratchet exists because a recap-bearing turn was already refused, and an override that widened it
 # back would hand the filter the exact request it just declined.
 PREFIX_NARROWNESS = ("minimal", "summary", "none")
+# The three modes as a TYPE, not a convention. It returned bare `str`, so assigning the result back
+# to `session.history_prefix_sent` (a Literal field) was a standing type error nobody could act on,
+# and a typo'd fourth mode would have been caught only by the ratchet quietly doing nothing.
+PrefixMode = Literal["minimal", "summary", "none"]
 
 
 @typechecked
-def effective_prefix_mode(session: AgentSession) -> str:
+def effective_prefix_mode(session: AgentSession) -> PrefixMode:
     """The persisted mode, narrowed by any one-turn override, consumed on read."""
     p_mode = session.history_prefix_mode
     p_once = session.history_prefix_once
     session.history_prefix_once = None
     if p_once is None:
         return p_mode
-    return max(p_mode, p_once, key=PREFIX_NARROWNESS.index)
+    p_widest: PrefixMode = max(p_mode, p_once, key=PREFIX_NARROWNESS.index)
+    return p_widest
 
 
 

backend/tests/test_chat_owns_its_app.py

@@ -113,8 +113,10 @@ def test_an_unselected_turn_reads_the_outputs_dir_ONCE():
     scans once and hands the rows down."""
     src = open(COMPOSER).read()
     i = src.index("p_app_ids = list(selected_app_output_ids or [])")
-    block = src[i:src.index("app_ctx = build_selected_app_context", i) + 400]
-    assert block.count("load_all()") == 1, "exactly one scan per turn"
+    block = src[i:src.index("if app_ctx:", i)]
+    # Count CALLS, not prose: the comment explaining the fix names load_all() too.
+    code = "\n".join(ln.split("#")[0] for ln in block.splitlines())
+    assert code.count("load_all()") == 1, f"exactly one scan per turn, found {code.count('load_all()')}"
     assert "apps_created_by_session(session.parent_session_id or session.id, p_outputs)" in block
     assert "build_unselected_app_context(p_outputs)" in block