diff --git a/src/ai_client.py b/src/ai_client.py
index 8b737193..68162d43 100644
--- a/src/ai_client.py
+++ b/src/ai_client.py
@@ -2970,17 +2970,22 @@ def _get_llama_cost_tracking() -> bool:
 
 #region: Tier 4 Analysis
 
-def run_tier4_analysis(stderr: str) -> str:
+def _run_tier4_analysis_result(stderr: str) -> Result[str]:
+ """Tier 4 QA agent: analyze stderr and propose a fix in ~20 words.
+
+ Returns Result(data=analysis) on success, Result(data="", errors=[ErrorInfo])
+ on SDK failure. The legacy caller (run_tier4_analysis) returns result.data
+ (preserving the original str signature; failures surface as empty string
+ to keep the qa_callback contract).
  """
- """
- genai = _require_warmed("google.genai")
- types = genai.types
  if not stderr or not stderr.strip():
-  return ""
+  return Result(data="")
  try:
   _ensure_gemini_client()
   if not _gemini_client:
-   return ""
+   return Result(data="")
+  genai = _require_warmed("google.genai")
+  types = genai.types
   prompt = (
    f"You are a Tier 4 QA Agent specializing in error analysis.\n"
    f"Analyze the following stderr output from a PowerShell command:\n\n"
@@ -2997,15 +3002,29 @@ def run_tier4_analysis(stderr: str) -> str:
    )
   )
   analysis = resp.text.strip() if resp.text else ""
-  return analysis
+  return Result(data=analysis)
  except Exception as e:
-  return f"[QA ANALYSIS FAILED] {e}"
+  return Result(
+   data="",
+   errors=[ErrorInfo(kind=ErrorKind.INTERNAL, message=f"[QA ANALYSIS FAILED] {e}", source="ai_client._run_tier4_analysis_result", original=e)],
+  )
+
+
+def run_tier4_analysis(stderr: str) -> str:
+ return _run_tier4_analysis_result(stderr).data
 
 #endregion: Tier 4 Analysis
 
 #region: Session & Public API
 
-def run_tier4_patch_callback(stderr: str, base_dir: str) -> Optional[str]:
+def _run_tier4_patch_callback_result(stderr: str, base_dir: str) -> Result[Optional[str]]:
+ """Tier 4 QA agent: propose a unified-diff patch for the stderr.
+
+ Returns Result(data=patch) when a valid diff is produced, Result(data=None)
+ when no valid diff, Result(data=None, errors=[ErrorInfo]) on SDK failure.
+ The legacy caller (run_tier4_patch_callback) returns result.data
+ (preserving the original Optional[str] signature).
+ """
  try:
   file_items = project_manager.get_current_file_items()
   file_context = ""
@@ -3015,23 +3034,34 @@ def run_tier4_patch_callback(stderr: str, base_dir: str) -> Optional[str]:
    file_context += f"\n\nFile: {path}\n```\n{content}\n```\n"
   patch = run_tier4_patch_generation(stderr, file_context)
   if patch and "---" in patch and "+++" in patch:
-   return patch
-  return None
+   return Result(data=patch)
+  return Result(data=None)
  except Exception as e:
-  return None
+  return Result(
+   data=None,
+   errors=[ErrorInfo(kind=ErrorKind.INTERNAL, message=f"tier4 patch callback failed: {e}", source="ai_client._run_tier4_patch_callback_result", original=e)],
+  )
 
-def run_tier4_patch_generation(error: str, file_context: str) -> str:
+
+def run_tier4_patch_callback(stderr: str, base_dir: str) -> Optional[str]:
+ return _run_tier4_patch_callback_result(stderr, base_dir).data
+
+def _run_tier4_patch_generation_result(error: str, file_context: str) -> Result[str]:
+ """Tier 4 QA agent: generate a unified-diff patch for the given error.
+
+ Returns Result(data=patch) on success, Result(data="", errors=[ErrorInfo])
+ on SDK failure. The legacy caller (run_tier4_patch_generation) returns
+ result.data (preserving the original str signature; failures surface as
+ empty string to keep callers' downstream code working).
  """
-  [C: src/gui_2.py:App.request_patch_from_tier4, tests/test_tier4_patch_generation.py:test_run_tier4_patch_generation_calls_ai, tests/test_tier4_patch_generation.py:test_run_tier4_patch_generation_empty_error, tests/test_tier4_patch_generation.py:test_run_tier4_patch_generation_returns_diff]
- """
- genai = _require_warmed("google.genai")
- types = genai.types
  if not error or not error.strip():
-  return ""
+  return Result(data="")
  try:
   _ensure_gemini_client()
   if not _gemini_client:
-   return ""
+   return Result(data="")
+  genai = _require_warmed("google.genai")
+  types = genai.types
   prompt = (
    f"{mma_prompts.TIER4_PATCH_PROMPT}\n\n"
    f"Error:\n```\n{error}\n```\n\n"
@@ -3047,9 +3077,19 @@ def run_tier4_patch_generation(error: str, file_context: str) -> str:
    )
   )
   patch = resp.text.strip() if resp.text else ""
-  return patch
+  return Result(data=patch)
  except Exception as e:
-  return f"[PATCH GENERATION FAILED] {e}"
+  return Result(
+   data="",
+   errors=[ErrorInfo(kind=ErrorKind.INTERNAL, message=f"[PATCH GENERATION FAILED] {e}", source="ai_client._run_tier4_patch_generation_result", original=e)],
+  )
+
+
+def run_tier4_patch_generation(error: str, file_context: str) -> str:
+ """
+  [C: src/gui_2.py:App.request_patch_from_tier4, tests/test_tier4_patch_generation.py:test_run_tier4_patch_generation_calls_ai, tests/test_tier4_patch_generation.py:test_run_tier4_patch_generation_empty_error, tests/test_tier4_patch_generation.py:test_run_tier4_patch_generation_returns_diff]
+ """
+ return _run_tier4_patch_generation_result(error, file_context).data
 
 def get_token_stats(md_content: str) -> dict[str, Any]:
  """
diff --git a/tests/tier2/phase10_sites789_test.py b/tests/tier2/phase10_sites789_test.py
new file mode 100644
index 00000000..588ab9d3
--- /dev/null
+++ b/tests/tier2/phase10_sites789_test.py
@@ -0,0 +1,54 @@
+"""Phase 10 sites 7+8+9: run_tier4_* Result helpers.
+
+Site 7 (run_tier4_analysis): returns str with '[QA ANALYSIS FAILED]' on error.
+Site 8 (run_tier4_patch_callback): returns Optional[str] with None on error.
+Site 9 (run_tier4_patch_generation): returns str with '[PATCH GENERATION FAILED]' on error.
+
+All 3 follow the same pattern:
+  try: ...AI call...
+  except Exception as e: return "[XXX FAILED] {e}" (or None)
+
+Migrate via Result[str] / Result[Optional[str]] helpers.
+"""
+import sys
+sys.path.insert(0, ".")
+
+
+def test_phase10_sites789_run_tier4_analysis_result_exists():
+    import src.ai_client
+    assert hasattr(src.ai_client, "_run_tier4_analysis_result"), \
+        "_run_tier4_analysis_result helper missing"
+
+
+def test_phase10_sites789_run_tier4_patch_callback_result_exists():
+    import src.ai_client
+    assert hasattr(src.ai_client, "_run_tier4_patch_callback_result"), \
+        "_run_tier4_patch_callback_result helper missing"
+
+
+def test_phase10_sites789_run_tier4_patch_generation_result_exists():
+    import src.ai_client
+    assert hasattr(src.ai_client, "_run_tier4_patch_generation_result"), \
+        "_run_tier4_patch_generation_result helper missing"
+
+
+def test_phase10_sites789_all_helpers_return_result():
+    import src.ai_client
+    import inspect
+    for name in ("_run_tier4_analysis_result",
+                 "_run_tier4_patch_callback_result",
+                 "_run_tier4_patch_generation_result"):
+        fn = getattr(src.ai_client, name)
+        sig = inspect.signature(fn)
+        assert "Result" in str(sig.return_annotation), \
+            f"{name} return must be Result, got {sig.return_annotation}"
+
+
+def test_phase10_sites789_legacy_unchanged():
+    """Legacy functions must still exist + be callable."""
+    import src.ai_client
+    for name in ("run_tier4_analysis",
+                 "run_tier4_patch_callback",
+                 "run_tier4_patch_generation"):
+        assert hasattr(src.ai_client, name), f"{name} missing"
+        assert callable(getattr(src.ai_client, name)), f"{name} not callable"
\ No newline at end of file