feat(plugins): per-source pattern attribution + explicit pre-screen rebuild proof

Two review items raised on #65449 (thanks @hansai-art):

1. Explicit test that post-module-load registration REBUILDS the
   _PREFIX_SUBSTRINGS pre-screen tuple — plugin patterns flow through
   the same fast path as built-ins, never around it. This was covered
   implicitly by the masking tests; now it is asserted directly.

2. Plugin patterns are now stored keyed by registration source, giving
   the #64229 lifecycle/ownership-ledger work a clean seam to drop one
   plugin's patterns on unload. No public removal API is added —
   additive-only stands; unload remains a host-owned lifecycle concern.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PnMCvi2vXqfs996AjVeF2F

agent/redact.py

@@ -1274,10 +1274,19 @@ def _has_known_prefix_substring(text: str) -> bool:
 # (``security.redact_secrets: false`` / HERMES_REDACT_SECRETS) applies to
 # plugin patterns exactly as it does to built-ins.
 
-_PLUGIN_PREFIX_PATTERNS: list = []
+# Keyed by registration source (e.g. "plugin:my-plugin") so the plugin
+# lifecycle/ownership-ledger work (#64229) has a clean seam to drop ONE
+# plugin's patterns on unload. There is deliberately no public removal
+# API — additive-only stands; unload is a host-owned lifecycle concern.
+_PLUGIN_PREFIX_PATTERNS: dict = {}
 _registry_lock = threading.Lock()
 
 
+def _plugin_patterns() -> list:
+    """All plugin-registered patterns in registration order."""
+    return [p for patterns in _PLUGIN_PREFIX_PATTERNS.values() for p in patterns]
+
+
 def _rebuild_prefix_matcher() -> None:
     """Recompile the prefix alternation and pre-screen substrings.
 
@@ -1286,7 +1295,7 @@ def _rebuild_prefix_matcher() -> None:
     under the GIL) propagates immediately to every caller.
     """
     global _PREFIX_RE, _PREFIX_SUBSTRINGS
-    combined = _PREFIX_PATTERNS + _PLUGIN_PREFIX_PATTERNS
+    combined = _PREFIX_PATTERNS + _plugin_patterns()
     _PREFIX_RE = re.compile(
         r"(?<![A-Za-z0-9_-])(" + "|".join(combined) + r")(?![A-Za-z0-9_-])"
     )
@@ -1365,14 +1374,14 @@ def register_redaction_patterns(patterns, source: str = "plugin") -> int:
                 source, pattern,
             )
             continue
-        if pattern in _PREFIX_PATTERNS or pattern in _PLUGIN_PREFIX_PATTERNS or pattern in accepted:
+        if pattern in _PREFIX_PATTERNS or pattern in _plugin_patterns() or pattern in accepted:
             logger.debug("%s: redaction pattern %r already registered", source, pattern)
             continue
         accepted.append(pattern)
 
     if accepted:
         with _registry_lock:
-            _PLUGIN_PREFIX_PATTERNS.extend(accepted)
+            _PLUGIN_PREFIX_PATTERNS.setdefault(source, []).extend(accepted)
             _rebuild_prefix_matcher()
         logger.info(
             "%s: registered %d redaction pattern(s)", source, len(accepted)

tests/test_redaction_registry.py

@@ -55,6 +55,28 @@ def test_registered_pattern_masks_token():
     assert "nvapi-" in out and "..." in out
 
 
+def test_prescreen_tuple_rebuilt_not_bypassed():
+    # The cheap pre-screen gate (_has_known_prefix_substring) consults
+    # _PREFIX_SUBSTRINGS. Registration after module load must REBUILD that
+    # tuple so plugin patterns flow through the same fast path as built-ins
+    # — never around it.
+    assert "nvapi-" not in redact_mod._PREFIX_SUBSTRINGS
+    assert not redact_mod._has_known_prefix_substring(f"x {NVAPI_KEY}")
+    register_redaction_patterns([NVAPI_PATTERN], source="test")
+    assert "nvapi-" in redact_mod._PREFIX_SUBSTRINGS
+    assert redact_mod._has_known_prefix_substring(f"x {NVAPI_KEY}")
+
+
+def test_patterns_attributed_per_source():
+    # Patterns are stored keyed by registration source — the seam the
+    # #64229 lifecycle/ledger path needs to drop one plugin's patterns on
+    # unload. No public removal API exists; additive-only stands.
+    register_redaction_patterns([NVAPI_PATTERN], source="plugin:alpha")
+    register_redaction_patterns([r"zk-[A-Za-z0-9]{24,}"], source="plugin:beta")
+    assert redact_mod._PLUGIN_PREFIX_PATTERNS["plugin:alpha"] == [NVAPI_PATTERN]
+    assert redact_mod._PLUGIN_PREFIX_PATTERNS["plugin:beta"] == [r"zk-[A-Za-z0-9]{24,}"]
+
+
 def test_builtins_unaffected_by_registration():
     register_redaction_patterns([NVAPI_PATTERN], source="test")
     sk = "sk-proj-AbCdEf1234567890GhIjKl"