fix: macOS browser/code-exec socket path exceeds Unix limit (#374)

macOS sets TMPDIR to /var/folders/xx/.../T/ (~51 chars). Combined with
agent-browser session names, socket paths reach 121 chars — exceeding
the 104-byte macOS AF_UNIX limit. This causes 'Screenshot file was not
created' errors and silent browser_vision failures on macOS.

Fix: use /tmp/ on macOS (symlink to /private/tmp, sticky-bit protected).
On Linux, tempfile.gettempdir() already returns /tmp — no behavior change.

Changes in browser_tool.py:
- Add _socket_safe_tmpdir() helper — returns /tmp on macOS, gettempdir()
  elsewhere
- Replace all 3 tempfile.gettempdir() calls for socket dirs
- Set mode=0o700 on socket dirs for privacy (was using default umask)
- Guard vision/text client init with try/except — a broken auxiliary
  config no longer prevents the entire browser_tool module from importing
  (which would disable all 10 browser tools, not just vision)
- Improve screenshot error messages with mode info and diagnostic hints
- Don't delete screenshots when LLM analysis fails — the capture was
  valid, only the vision API call failed. Screenshots are still cleaned
  up by the existing 24-hour _cleanup_old_screenshots mechanism.

Changes in code_execution_tool.py:
- Same /tmp fix for RPC socket path (was 103 chars on macOS — one char
  from the 104-byte limit)

tools/code_execution_tool.py

@@ -385,7 +385,11 @@ def execute_code(
 
     # --- Set up temp directory with hermes_tools.py and script.py ---
     tmpdir = tempfile.mkdtemp(prefix="hermes_sandbox_")
-    sock_path = os.path.join(tempfile.gettempdir(), f"hermes_rpc_{uuid.uuid4().hex}.sock")
+    # Use /tmp on macOS to avoid the long /var/folders/... path that pushes
+    # Unix domain socket paths past the 104-byte macOS AF_UNIX limit.
+    # On Linux, tempfile.gettempdir() already returns /tmp.
+    _sock_tmpdir = "/tmp" if sys.platform == "darwin" else tempfile.gettempdir()
+    sock_path = os.path.join(_sock_tmpdir, f"hermes_rpc_{uuid.uuid4().hex}.sock")
 
     tool_call_log: list = []
     tool_call_counter = [0]  # mutable so the RPC thread can increment