fix(gateway): diagnosable MEDIA rejections + canonical cache roots + null-path guard

Operators can now see which MEDIA path was dropped and why, generated
artifacts under the canonical ~/.hermes/cache/{images,...} layout deliver,
and a crafted ~\x00 path no longer aborts the whole attachment batch.

- MEDIA_DELIVERY_SAFE_ROOTS: add canonical cache/{images,audio,videos,
  documents,screenshots} alongside the legacy *_cache dirs (#31733).
- filter_media/local_delivery_paths: log the rejected path (was a blind
  "outside allowed roots") via _log_safe_path, which strips control chars
  and Unicode line separators so a model-emitted path can't forge a log line.
- validate_media_delivery_path + extract_media: guard os.path.expanduser
  so a ~\x00 path returns None / is skipped instead of raising and dropping
  every other attachment in the response.

Salvaged and slimmed from #33251 (780 LOC -> 35): the reason-tag taxonomy,
the parts-eliding redactor, and the extension-partition hoist are dropped in
favor of logging the path directly. All three findings were verified and
reproduced by the contributor.

Co-authored-by: wysie <wysie@users.noreply.github.com>

gateway/platforms/base.py

@@ -848,6 +848,13 @@ MEDIA_DELIVERY_SAFE_ROOTS = (
     _HERMES_HOME / "video_cache",
     _HERMES_HOME / "document_cache",
     _HERMES_HOME / "browser_screenshots",
+    # Canonical cache layout — listed alongside the legacy *_cache dirs so
+    # generated artifacts deliver on installs that have both (#31733).
+    _HERMES_HOME / "cache" / "images",
+    _HERMES_HOME / "cache" / "audio",
+    _HERMES_HOME / "cache" / "videos",
+    _HERMES_HOME / "cache" / "documents",
+    _HERMES_HOME / "cache" / "screenshots",
 )
 
 # Default recency window for trusting freshly-produced files (seconds).
@@ -1022,7 +1029,11 @@ def validate_media_delivery_path(path: str) -> Optional[str]:
     if not candidate:
         return None
 
-    expanded = Path(os.path.expanduser(candidate))
+    try:
+        expanded = Path(os.path.expanduser(candidate))
+    except (OSError, RuntimeError, ValueError):
+        # expanduser raises ValueError("embedded null byte") for a ~\x00 path.
+        return None
     if not expanded.is_absolute():
         return None
 
@@ -1066,6 +1077,17 @@ def validate_media_delivery_path(path: str) -> Optional[str]:
     return None
 
 
+# Neutralise control chars and the Unicode line separators (NEL, LS, PS) that
+# str.splitlines() / log aggregators treat as breaks, so a model-emitted path
+# can't forge a second log line. Truncated to keep records bounded.
+_LOG_UNSAFE_CHARS = re.compile(r"[\x00-\x1f\x7f\x85\u2028\u2029]")
+
+
+def _log_safe_path(path: str) -> str:
+    """Return a single-line, length-bounded path for log output."""
+    return _LOG_UNSAFE_CHARS.sub("?", str(path))[:200]
+
+
 SUPPORTED_DOCUMENT_TYPES = {
     ".pdf": "application/pdf",
     ".md": "text/markdown",
@@ -2438,11 +2460,12 @@ class BasePlatformAdapter(ABC):
         """Drop unsafe MEDIA paths and normalize accepted paths."""
         safe_media: List[Tuple[str, bool]] = []
         for media_path, is_voice in media_files or []:
-            safe_path = validate_media_delivery_path(str(media_path))
+            raw = str(media_path)
+            safe_path = validate_media_delivery_path(raw)
             if safe_path:
                 safe_media.append((safe_path, bool(is_voice)))
             else:
-                logger.warning("Skipping unsafe MEDIA directive path outside allowed roots")
+                logger.warning("Skipping unsafe MEDIA directive path: %s", _log_safe_path(raw))
         return safe_media
 
     @staticmethod
@@ -2450,11 +2473,12 @@ class BasePlatformAdapter(ABC):
         """Drop unsafe bare local file paths and normalize accepted paths."""
         safe_paths: List[str] = []
         for file_path in file_paths or []:
-            safe_path = validate_media_delivery_path(str(file_path))
+            raw = str(file_path)
+            safe_path = validate_media_delivery_path(raw)
             if safe_path:
                 safe_paths.append(safe_path)
             else:
-                logger.warning("Skipping unsafe local file path outside allowed roots")
+                logger.warning("Skipping unsafe local file path: %s", _log_safe_path(raw))
         return safe_paths
 
     @staticmethod
@@ -2505,7 +2529,12 @@ class BasePlatformAdapter(ABC):
                 path = path[1:-1].strip()
             path = path.lstrip("`\"'").rstrip("`\"',.;:)}]")
             if path:
-                media.append((os.path.expanduser(path), has_voice_tag))
+                try:
+                    media.append((os.path.expanduser(path), has_voice_tag))
+                except (OSError, RuntimeError, ValueError):
+                    # Skip a crafted ~\x00 path rather than aborting extraction
+                    # and dropping every other attachment in the response.
+                    continue
 
         # Remove MEDIA tags from content (including surrounding quote/backtick wrappers)
         if media: