diff --git a/tests/tools/test_file_tools.py b/tests/tools/test_file_tools.py
index b009c009f25dc..329247ec313dc 100644
--- a/tests/tools/test_file_tools.py
+++ b/tests/tools/test_file_tools.py
@@ -459,6 +459,20 @@ class TestSensitivePathCheck:
         assert "error" in result
         assert "sensitive system path" in result["error"]
 
+    def test_macos_private_var_carveouts(self):
+        """macOS temp dirs under /private/var must not be blanket-blocked,
+        while the genuinely-sensitive /private/var subtrees still are."""
+        from tools.file_tools import _check_sensitive_path
+
+        # $TMPDIR / /tmp / /var/folders realpath into these on macOS.
+        assert _check_sensitive_path("/private/var/folders/xy/T/tmp.txt") is None
+        assert _check_sensitive_path("/private/var/tmp/build.log") is None
+        # Sensitive subtrees remain blocked.
+        assert _check_sensitive_path("/private/var/db/secret") is not None
+        assert _check_sensitive_path("/private/var/root/x") is not None
+        # /etc (and its macOS /private/etc mirror) stay blocked.
+        assert _check_sensitive_path("/private/etc/hosts") is not None
+
     @patch("tools.file_tools._get_file_ops")
     def test_normal_file_not_blocked(self, mock_get, monkeypatch):
         monkeypatch.setattr("tools.file_tools._hermes_config_resolved", "/home/user/.hermes/config.yaml")
diff --git a/tests/tools/test_fuzzy_match.py b/tests/tools/test_fuzzy_match.py
index e8d0f2a4808ae..f602aa5ad710a 100644
--- a/tests/tools/test_fuzzy_match.py
+++ b/tests/tools/test_fuzzy_match.py
@@ -11,6 +11,20 @@ class TestExactMatch:
         assert count == 1
         assert new == "hi world"
 
+    def test_whitespace_only_old_string_rejected(self):
+        """A whitespace-only old_string is not a meaningful anchor."""
+        content = "alpha\n   \nbeta\n"
+        new, count, _, err = fuzzy_find_and_replace(content, "   ", "XXX")
+        assert count == 0
+        assert err is not None
+        assert "whitespace" in err
+        assert new == content  # untouched
+
+    def test_empty_old_string_rejected(self):
+        new, count, _, err = fuzzy_find_and_replace("abc", "", "x")
+        assert count == 0
+        assert err is not None
+
 
     def test_multiline_exact(self):
         content = "line1\nline2\nline3"
diff --git a/tests/tools/test_terminal_foreground_timeout_cap.py b/tests/tools/test_terminal_foreground_timeout_cap.py
index f18807bbc1a76..0081de88a50d0 100644
--- a/tests/tools/test_terminal_foreground_timeout_cap.py
+++ b/tests/tools/test_terminal_foreground_timeout_cap.py
@@ -47,6 +47,28 @@ class TestForegroundTimeoutCap:
         assert str(FOREGROUND_MAX_TIMEOUT) in result["error"]
         assert "background=true" in result["error"]
 
+    def test_zero_timeout_rejected(self):
+        """timeout=0 must be rejected, not silently coerced to the default."""
+        from tools.terminal_tool import terminal_tool
+
+        with patch("tools.terminal_tool._get_env_config", return_value=_make_env_config()), \
+             patch("tools.terminal_tool._start_cleanup_thread"):
+            result = json.loads(terminal_tool(command="echo hi", timeout=0))
+
+        assert result.get("error")
+        assert "positive" in result["error"]
+
+    def test_negative_timeout_rejected(self):
+        """timeout=-1 must be rejected, not fire an immediate '-1s' timeout."""
+        from tools.terminal_tool import terminal_tool
+
+        with patch("tools.terminal_tool._get_env_config", return_value=_make_env_config()), \
+             patch("tools.terminal_tool._start_cleanup_thread"):
+            result = json.loads(terminal_tool(command="echo hi", timeout=-1))
+
+        assert result.get("error")
+        assert "positive" in result["error"]
+
 
     def test_foreground_allows_help_variant_for_server_command(self):
         """Informational variants like '--help' should not be blocked."""
diff --git a/tools/file_tools.py b/tools/file_tools.py
index a31ec7432e0a9..9a9590c9f7f5c 100644
--- a/tools/file_tools.py
+++ b/tools/file_tools.py
@@ -641,7 +641,13 @@ def _filter_read_blocked_search_results(result, task_id: str = "default") -> int
 # terminal tool's approval system.  These match prefixes after os.path.realpath.
 _SENSITIVE_PATH_PREFIXES = (
     "/etc/", "/boot/", "/usr/lib/systemd/",
-    "/private/etc/", "/private/var/",
+    "/private/etc/",
+    # macOS: /private/var mirrors /var. Block the sensitive subtrees, NOT the
+    # whole thing — a blanket "/private/var/" refused every legitimate temp-file
+    # write, because $TMPDIR, /tmp, and /var/folders all realpath() into
+    # /private/var/folders/... on macOS (and _resolve_path_for_task resolves
+    # symlinks), and /private/var/tmp is a normal temp dir.
+    "/private/var/db/", "/private/var/root/",
 )
 _SENSITIVE_EXACT_PATHS = {"/var/run/docker.sock", "/run/docker.sock"}
 
diff --git a/tools/fuzzy_match.py b/tools/fuzzy_match.py
index 3f599e7b2ac05..44a7885855a39 100644
--- a/tools/fuzzy_match.py
+++ b/tools/fuzzy_match.py
@@ -83,6 +83,13 @@ def fuzzy_find_and_replace(content: str, old_string: str, new_string: str,
     if not old_string:
         return content, 0, None, "old_string cannot be empty"
 
+    if not old_string.strip():
+        # A whitespace-only old_string matches trivially (a blank line, run of
+        # spaces, etc.) and, when it recurs, either mass-replaces under
+        # replace_all or raises a hard-to-diagnose ambiguity error. It's never
+        # a meaningful anchor — reject it so the caller provides real context.
+        return content, 0, None, "old_string is only whitespace — provide non-blank text to match"
+
     if old_string == new_string:
         return content, 0, None, "old_string and new_string are identical"
 
diff --git a/tools/terminal_tool.py b/tools/terminal_tool.py
index 5ebf349ae8a19..7f9141ff8a9ef 100644
--- a/tools/terminal_tool.py
+++ b/tools/terminal_tool.py
@@ -2307,6 +2307,16 @@ def terminal_tool(
                 )
             cwd = config["cwd"]
         default_timeout = config["timeout"]
+
+        # Validate an explicit timeout before it flows into deadline math.
+        # ``timeout or default`` silently turns 0 into the default (0 can't mean
+        # "no timeout" here), and a negative value is truthy so it would sail
+        # through to ``deadline = now + timeout`` and fire an immediate,
+        # nonsensical "-Ns" timeout. Reject non-positive values outright.
+        if timeout is not None and timeout <= 0:
+            return tool_error(
+                f"timeout must be a positive number of seconds (got {timeout})."
+            )
         effective_timeout = timeout or default_timeout
 
         # Reject foreground commands where the model explicitly requests