Harden reliability, security, and UX across core modules

- Add thread safety: _anthropic_history_lock and _send_lock in ai_client to prevent concurrent corruption
  - Add _send_thread_lock in gui_2 for atomic check-and-start of send thread
  - Add atexit fallback in session_logger to flush log files on abnormal exit
  - Fix file descriptor leaks: use context managers for urlopen in mcp_client
  - Cap unbounded tool output growth at 500KB per send() call (both Gemini and Anthropic)
  - Harden path traversal: resolve(strict=True) with fallback in mcp_client allowlist checks
  - Add SLOP_CREDENTIALS env var override for credentials.toml with helpful error message
  - Fix Gemini token heuristic: use _CHARS_PER_TOKEN (3.5) instead of hardcoded // 4
  - Add keyboard shortcuts: Ctrl+Enter to send, Ctrl+L to clear message input
  - Add auto-save: flush project and config to disk every 60 seconds

mcp_client.py

@@ -65,7 +65,10 @@ def configure(file_items: list[dict], extra_base_dirs: list[str] | None = None):
     for item in file_items:
         p = item.get("path")
         if p is not None:
-            rp = Path(p).resolve()
+            try:
+                rp = Path(p).resolve(strict=True)
+            except (OSError, ValueError):
+                rp = Path(p).resolve()
             _allowed_paths.add(rp)
             _base_dirs.add(rp.parent)
 
@@ -82,8 +85,13 @@ def _is_allowed(path: Path) -> bool:
     A path is allowed if:
       - it is explicitly in _allowed_paths, OR
       - it is contained within (or equal to) one of the _base_dirs
+    All paths are resolved (follows symlinks) before comparison to prevent
+    symlink-based path traversal.
     """
-    rp = path.resolve()
+    try:
+        rp = path.resolve(strict=True)
+    except (OSError, ValueError):
+        rp = path.resolve()
     if rp in _allowed_paths:
         return True
     for bd in _base_dirs:
@@ -104,7 +112,10 @@ def _resolve_and_check(raw_path: str) -> tuple[Path | None, str]:
         p = Path(raw_path)
         if not p.is_absolute() and _primary_base_dir:
             p = _primary_base_dir / p
-        p = p.resolve()
+        try:
+            p = p.resolve(strict=True)
+        except (OSError, ValueError):
+            p = p.resolve()
     except Exception as e:
         return None, f"ERROR: invalid path '{raw_path}': {e}"
     if not _is_allowed(p):
@@ -269,7 +280,8 @@ def web_search(query: str) -> str:
     url = "https://html.duckduckgo.com/html/?q=" + urllib.parse.quote(query)
     req = urllib.request.Request(url, headers={'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64)'})
     try:
-        html = urllib.request.urlopen(req, timeout=10).read().decode('utf-8', errors='ignore')
+        with urllib.request.urlopen(req, timeout=10) as resp:
+            html = resp.read().decode('utf-8', errors='ignore')
         parser = _DDGParser()
         parser.feed(html)
         if not parser.results:
@@ -292,7 +304,8 @@ def fetch_url(url: str) -> str:
 
     req = urllib.request.Request(url, headers={'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64)'})
     try:
-        html = urllib.request.urlopen(req, timeout=10).read().decode('utf-8', errors='ignore')
+        with urllib.request.urlopen(req, timeout=10) as resp:
+            html = resp.read().decode('utf-8', errors='ignore')
         parser = _TextExtractor()
         parser.feed(html)
         full_text = " ".join(parser.text)