fix: preserve native model switches and bound project searches

agent/search_policy.py

@@ -8,6 +8,66 @@ path; broad diagnostic probes should apply this policy to recursive walks.
 
 from __future__ import annotations
 
+from pathlib import Path
+
+SEARCH_RG_THREADS = 2
+SEARCH_MAX_CONCURRENT = 2
+
+_PROJECT_MARKERS = ('.git', '.hg', 'pyproject.toml', 'package.json',
+                    'Cargo.toml', 'go.mod', 'CMakeLists.txt')
+
+
+def _project_root(path):
+    """Prefer the enclosing repository over nested monorepo packages."""
+    package = None
+    for parent in (path, *path.parents):
+        if (parent / '.git').exists() or (parent / '.hg').exists():
+            return parent
+        if package is None and any((parent / marker).exists() for marker in _PROJECT_MARKERS):
+            package = parent
+    return package
+
+
+def local_search_scope(path, cwd, home):
+    """Resolve broad local roots without starting a recursive search process.
+
+    Returns (root, notice, error). Only one level of candidate directories is
+    inspected; no repository-wide discovery is needed to reject an umbrella.
+    Real paths prevent symlink aliases from bypassing broad-root detection.
+    """
+    root = Path(path)
+    if not root.is_absolute():
+        root = Path(cwd) / root
+    root = root.resolve()
+    if not root.is_dir():
+        return path, None, None
+    home = Path(home).resolve()
+    project = _project_root(Path(cwd).resolve())
+    root_project = _project_root(root)
+    if root_project is not None:
+        return path, None, None
+    candidates = []
+    try:
+        # Bound metadata work even in directories containing many entries.
+        from itertools import islice
+        for child in islice(root.iterdir(), 256):
+            if child.name in SEARCH_PRUNE_DIR_NAMES or not child.is_dir():
+                continue
+            if any((child / marker).exists() for marker in _PROJECT_MARKERS):
+                candidates.append(str(child))
+    except OSError:
+        pass
+    broad = (root == Path(root.anchor) or root == home or root in home.parents
+             or len(candidates) > 1 or (project is not None and root in project.parents))
+    if not broad:
+        return path, None, None
+    if project is not None and root in project.parents:
+        chosen = str(project)
+        return chosen, f'Search scoped to current project: {chosen}. Set allow_broad=true for the requested umbrella.', None
+    choices = ', '.join(sorted(candidates)[:12]) or 'choose an explicit project directory'
+    return path, None, ('Search scope needed: requested root spans projects or a home/drive. '
+                        f'Candidates: {choices}. Set allow_broad=true only for an intentional broad search.')
+
 
 # Keep this policy conservative and name-based so it works for local and remote
 # shell backends alike. The same set is used by context discovery and search