conductor(plan): mark Phase 10 complete (ai_client Batch B; BC 9->0)

Phase 10: ai_client Batch B (9 INTERNAL_BROAD_CATCH sites migrated via 7 helpers).

Helpers added to src/ai_client.py:
- _list_gemini_models_result (site 1)
- _delete_gemini_cache_result (sites 2+3)
- _should_cache_gemini_result (site 4)
- _create_gemini_cache_result (site 5)
- _send_cli_round_result (site 6)
- _run_tier4_analysis_result (site 7)
- _run_tier4_patch_callback_result (site 8)
- _run_tier4_patch_generation_result (site 9)

Per-site decision (TIER1_REVIEW):
- Sites with broad except Exception + log/_append_comms: MIGRATE to Result[T]
- Site 6 with events.emit + raise: extract Result variant; inner re-raises
  original exception to preserve outer _send_gemini_cli catch flow
- Sites 7+9 with empty-default ('[XXX FAILED] {e}'): MIGRATE to Result[T]

Audit state (after Phase 10):
  mcp_client: 0 migration-target (Phase 3-8 complete)
  ai_client:  27 -> 18 migration-target
              BC: 9 -> 0 ✓
              SS: 11 (Phase 11)
              RETHROW: 6 (Phase 12; was 7; -1 from migration)
              COMPLIANT: 19 -> 27 (+8 from helpers)
  rag_engine: 9 migration-target (Phase 13)

Tests: 79 pass (47 prior + 32 Phase 10 site tests + 3 invariant).

tests/tier2/phase10_invariant_test.py

@@ -0,0 +1,63 @@
+"""Phase 10 invariant tests (GREEN).
+
+9 BC sites migrated via 7 helpers:
+- _list_gemini_models_result (site 1)
+- _delete_gemini_cache_result (sites 2+3)
+- _should_cache_gemini_result (site 4)
+- _create_gemini_cache_result (site 5)
+- _send_cli_round_result (site 6)
+- _run_tier4_analysis_result (site 7)
+- _run_tier4_patch_callback_result (site 8)
+- _run_tier4_patch_generation_result (site 9)
+"""
+import sys
+sys.path.insert(0, ".")
+
+
+def test_phase10_ai_client_bc_count_zero():
+    """After Phase 10: ai_client BC count is 0 (was 17 at baseline)."""
+    import json
+    import subprocess
+    r = subprocess.run(
+        ["uv", "run", "python", "scripts/audit_exception_handling.py",
+         "--include-baseline", "--json"],
+        capture_output=True, text=True
+    )
+    data = json.loads(r.stdout)
+    files = {f["filename"]: f for f in data["files"]}
+    ai = files["src\\ai_client.py"]
+    bc = sum(1 for x in ai["findings"] if x["category"] == "INTERNAL_BROAD_CATCH")
+    assert bc == 0, f"expected ai_client BC=0 after Phase 10, got {bc}"
+
+
+def test_phase10_all_helpers_exist():
+    """All 7 new _result helpers must exist on ai_client."""
+    import src.ai_client
+    expected = [
+        "_list_gemini_models_result",
+        "_delete_gemini_cache_result",
+        "_should_cache_gemini_result",
+        "_create_gemini_cache_result",
+        "_send_cli_round_result",
+        "_run_tier4_analysis_result",
+        "_run_tier4_patch_callback_result",
+        "_run_tier4_patch_generation_result",
+    ]
+    for name in expected:
+        assert hasattr(src.ai_client, name), f"{name} helper missing from src.ai_client"
+
+
+def test_phase10_legacy_functions_preserved():
+    """All legacy functions must still be callable with original signatures."""
+    import src.ai_client
+    legacy = [
+        "_list_gemini_models",
+        "_send_gemini",
+        "_send_gemini_cli",
+        "run_tier4_analysis",
+        "run_tier4_patch_callback",
+        "run_tier4_patch_generation",
+    ]
+    for name in legacy:
+        assert hasattr(src.ai_client, name), f"{name} legacy function missing"
+        assert callable(getattr(src.ai_client, name)), f"{name} not callable"