fix(R6): fall back to interaction.project when LLM returns empty

Codex R6: the LLM extractor accepted the model's project field
verbatim. When the model returned empty string, clearly p06 memories
got promoted as project='', making them invisible to the p06
project-memory band and explaining the p06-offline-design harness
failure.

Fix: if model returns empty project but interaction.project is set,
inherit the interaction's project. Model-supplied project still takes
precedence when non-empty.

Two new tests lock the fallback and precedence behaviors.
R5 acknowledged (LLM extractor not yet wired into API — next task).

Test count: 278 -> 280. Harness re-run pending after deploy.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/test_extractor_llm.py

@@ -97,6 +97,25 @@ def test_parser_tags_version_and_rule():
     assert result[0].source_interaction_id == "test-id"
 
 
+def test_parser_falls_back_to_interaction_project():
+    """R6: when the model returns empty project but the interaction
+    has one, the candidate should inherit the interaction's project."""
+    raw = '[{"type": "project", "content": "machine works offline"}]'
+    interaction = _make_interaction()
+    interaction.project = "p06-polisher"
+    result = _parse_candidates(raw, interaction)
+    assert result[0].project == "p06-polisher"
+
+
+def test_parser_keeps_model_project_when_provided():
+    """Model-supplied project takes precedence over interaction."""
+    raw = '[{"type": "project", "content": "x", "project": "p04-gigabit"}]'
+    interaction = _make_interaction()
+    interaction.project = "p06-polisher"
+    result = _parse_candidates(raw, interaction)
+    assert result[0].project == "p04-gigabit"
+
+
 def test_missing_cli_returns_empty(monkeypatch):
     """If ``claude`` is not on PATH the extractor returns empty, never raises."""
     monkeypatch.setattr(extractor_llm, "_cli_available", lambda: False)