fix: remove self-defeating assert_safe_path from vault modules, clarify traversal test scope

vault/reader.py, vault/writer.py: removed assert_safe_path() calls — that guard is
for protecting the vault FROM external modules, not from within vault code itself.
Vault security comes from BLOCKED_PREFIXES preventing memory/reader from entering vault.

test_path_traversal.py: split into REAL_TRAVERSAL (blocks read+write) vs
READ_ONLY_SAFE patterns (URL-encoded, backslash — harmless on Python/macOS because
Path does not decode percent-encoding; raises FileNotFoundError on read only).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/pyra/vault/reader.py

@@ -1,16 +1,13 @@
 import json
 from pathlib import Path
 
-from pyra.security.boundaries import assert_safe_path
 from pyra.utils.paths import pyra_home, safe_chmod
 
 _KEYS_FILE = pyra_home() / "vault" / "secrets" / "api_keys.json"
 
 
 def get_key(provider_id: str) -> str | None:
-    """Read an API key from the vault. Never exposed to the AI."""
-    assert_safe_path(_KEYS_FILE)  # defense-in-depth
-
+    """Read an API key from the vault. Called only by the chat session, not by the AI."""
     if not _KEYS_FILE.exists():
         return None
 

src/pyra/vault/writer.py

@@ -1,7 +1,6 @@
 import json
 from pathlib import Path
 
-from pyra.security.boundaries import assert_safe_path
 from pyra.utils.paths import ensure_dir, pyra_home, safe_chmod
 
 _KEYS_FILE = pyra_home() / "vault" / "secrets" / "api_keys.json"
@@ -9,8 +8,6 @@ _KEYS_FILE = pyra_home() / "vault" / "secrets" / "api_keys.json"
 
 def set_key(provider_id: str, api_key: str) -> None:
     """Store an API key in the vault. Called only by the setup wizard."""
-    assert_safe_path(_KEYS_FILE)  # defense-in-depth
-
     ensure_dir(_KEYS_FILE.parent, 0o700)
 
     # Temporarily make writable to update
@@ -28,8 +25,6 @@ def set_key(provider_id: str, api_key: str) -> None:
 
 def delete_key(provider_id: str) -> bool:
     """Remove an API key from the vault. Returns True if key existed."""
-    assert_safe_path(_KEYS_FILE)
-
     if not _KEYS_FILE.exists():
         return False