Fix create_skill wedge: short-circuit single-option navigation, never leave scheduler busy

An empty category produced a one-option SemIf leaf decision; the backend rejects
<2 options, the ValueError unwound past the current-process reset, and every
later request queued forever behind a phantom current. Navigation now
short-circuits empty trees/categories straight to the create branch (no SemIf
decision when there's nothing to choose), and the scheduler clears its current
process even when dispatch raises. Authoring generation is capped at 128 tokens.

tests/test_skills.py

@@ -9,9 +9,11 @@ import pytest
 
 from semif_agent.decisions import Request
 from semif_agent.engine import EngineConfig, EngineUnavailable, SemIfEngine
+from semif_agent.log import DecisionLog
 from semif_agent.skills import (
     CategoryDraft,
     CategoryRegistry,
+    CreateCategory,
     SkillDraft,
     build_category_prompt,
     build_skill_prompt,
@@ -20,9 +22,11 @@ from semif_agent.skills import (
     generate_category,
     generate_skill,
     merge_registry,
+    navigate,
     parse_category_draft,
     parse_skill_draft,
 )
+from semif_agent.trace import TraceLog
 
 
 def test_build_category_prompt_contains_request_and_tree():
@@ -177,4 +181,14 @@ def test_merge_registry_loads_categories_and_skills(tmp_path):
     merge_registry(tree, registry.read())
     names = [s.name for s in tree["delivery"]]
     assert names == ["track_live"]
-    assert tree["delivery"][0].category == "delivery"
+    assert tree["delivery"][0].category == "delivery"
+
+
+def test_navigate_empty_tree_short_circuits(tmp_path):
+    """An empty tree goes straight to CreateCategory without a SemIf call."""
+    log = DecisionLog(str(tmp_path / "decisions.jsonl"))
+    trace = TraceLog(str(tmp_path / "runs.jsonl"))
+    result = navigate(None, log, trace, Request("anything"), {})
+    assert isinstance(result, CreateCategory)
+    assert log.read() == []
+    assert any(e["kind"] == "create_category" for e in trace.read())