feat: add inline diff previews for write actions

Show inline diffs in the CLI transcript when write_file, patch, or
skill_manage modifies files. Captures a filesystem snapshot before the
tool runs, computes a unified diff after, and renders it with ANSI
coloring in the activity feed.

Adds tool_start_callback and tool_complete_callback hooks to AIAgent
for pre/post tool execution notifications.

Also fixes _extract_parallel_scope_path to normalize relative paths
to absolute, preventing the parallel overlap detection from missing
conflicts when the same file is referenced with different path styles.

Gated by display.inline_diffs config option (default: true).

Based on PR #3774 by @kshitijk4poor.

run_agent.py

@@ -320,8 +320,12 @@ def _extract_parallel_scope_path(tool_name: str, function_args: dict) -> Path |
     if not isinstance(raw_path, str) or not raw_path.strip():
         return None
 
+    expanded = Path(raw_path).expanduser()
+    if expanded.is_absolute():
+        return Path(os.path.abspath(str(expanded)))
+
     # Avoid resolve(); the file may not exist yet.
-    return Path(raw_path).expanduser()
+    return Path(os.path.abspath(str(Path.cwd() / expanded)))
 
 
 def _paths_overlap(left: Path, right: Path) -> bool:
@@ -486,6 +490,8 @@ class AIAgent:
         provider_data_collection: str = None,
         session_id: str = None,
         tool_progress_callback: callable = None,
+        tool_start_callback: callable = None,
+        tool_complete_callback: callable = None,
         thinking_callback: callable = None,
         reasoning_callback: callable = None,
         clarify_callback: callable = None,
@@ -620,6 +626,8 @@ class AIAgent:
             ).start()
 
         self.tool_progress_callback = tool_progress_callback
+        self.tool_start_callback = tool_start_callback
+        self.tool_complete_callback = tool_complete_callback
         self.thinking_callback = thinking_callback
         self.reasoning_callback = reasoning_callback
         self._reasoning_deltas_fired = False  # Set by _fire_reasoning_delta, reset per API call
@@ -5553,7 +5561,7 @@ class AIAgent:
                     args_preview = args_str[:self.log_prefix_chars] + "..." if len(args_str) > self.log_prefix_chars else args_str
                     print(f"  📞 Tool {i}: {name}({list(args.keys())}) - {args_preview}")
 
-        for _, name, args in parsed_calls:
+        for tc, name, args in parsed_calls:
             if self.tool_progress_callback:
                 try:
                     preview = _build_tool_preview(name, args)
@@ -5561,6 +5569,13 @@ class AIAgent:
                 except Exception as cb_err:
                     logging.debug(f"Tool progress callback error: {cb_err}")
 
+        for tc, name, args in parsed_calls:
+            if self.tool_start_callback:
+                try:
+                    self.tool_start_callback(tc.id, name, args)
+                except Exception as cb_err:
+                    logging.debug(f"Tool start callback error: {cb_err}")
+
         # ── Concurrent execution ─────────────────────────────────────────
         # Each slot holds (function_name, function_args, function_result, duration, error_flag)
         results = [None] * num_tools
@@ -5631,6 +5646,12 @@ class AIAgent:
                     response_preview = function_result[:self.log_prefix_chars] + "..." if len(function_result) > self.log_prefix_chars else function_result
                     print(f"  ✅ Tool {i+1} completed in {tool_duration:.2f}s - {response_preview}")
 
+            if self.tool_complete_callback:
+                try:
+                    self.tool_complete_callback(tc.id, name, args, function_result)
+                except Exception as cb_err:
+                    logging.debug(f"Tool complete callback error: {cb_err}")
+
             # Truncate oversized results
             MAX_TOOL_RESULT_CHARS = 100_000
             if len(function_result) > MAX_TOOL_RESULT_CHARS:
@@ -5719,6 +5740,12 @@ class AIAgent:
                 except Exception as cb_err:
                     logging.debug(f"Tool progress callback error: {cb_err}")
 
+            if self.tool_start_callback:
+                try:
+                    self.tool_start_callback(tool_call.id, function_name, function_args)
+                except Exception as cb_err:
+                    logging.debug(f"Tool start callback error: {cb_err}")
+
             # Checkpoint: snapshot working dir before file-mutating tools
             if function_name in ("write_file", "patch") and self._checkpoint_mgr.enabled:
                 try:
@@ -5883,6 +5910,12 @@ class AIAgent:
                 logging.debug(f"Tool {function_name} completed in {tool_duration:.2f}s")
                 logging.debug(f"Tool result ({len(function_result)} chars): {function_result}")
 
+            if self.tool_complete_callback:
+                try:
+                    self.tool_complete_callback(tool_call.id, function_name, function_args, function_result)
+                except Exception as cb_err:
+                    logging.debug(f"Tool complete callback error: {cb_err}")
+
             # Guard against tools returning absurdly large content that would
             # blow up the context window. 100K chars ≈ 25K tokens — generous
             # enough for any reasonable tool output but prevents catastrophic