test(redact): add YAML ReDoS test, strengthen existing test with keyword

- Relax timing bound from 1.0s to 2.0s (CI machine robustness).
- Add test_long_dotted_run_with_keyword_completes_fast: includes a secret
  keyword so the pre-gate does NOT skip _CFG_DOTTED_RE — directly exercises
  the possessive-quantifier regex, not just the pre-gate.
- Add test_yaml_assign_redos_resistance: _YAML_ASSIGN_RE was modified but
  had no ReDoS test — add 100-line stress input.
- Add test_yaml_assign_secret_still_redacted: verify YAML matching behavior
  preserved with possessive quantifiers.

tests/agent/test_redact.py

@@ -560,7 +560,22 @@ class TestConfigKeyRedosResistance:
         text = ".".join(["segment"] * 100) + " end"
         t0 = time.perf_counter()
         assert redact_sensitive_text(text) == text
-        assert time.perf_counter() - t0 < 1.0
+        assert time.perf_counter() - t0 < 2.0
+
+    def test_long_dotted_run_with_keyword_completes_fast(self):
+        """Exercise _CFG_DOTTED_RE directly (bypasses the keyword pre-gate).
+
+        The pre-gate skips the regex when no secret keyword is present, so
+        test_long_dotted_run_completes_fast only guards the pre-gate.  This
+        test includes a keyword but no '=' so the regex runs and must still
+        complete quickly thanks to the possessive quantifiers.
+        """
+        import time
+
+        text = ".".join(["segment"] * 100) + ".token end"
+        t0 = time.perf_counter()
+        assert redact_sensitive_text(text) == text
+        assert time.perf_counter() - t0 < 2.0
 
     def test_long_dotted_secret_still_redacted(self):
         # Possessive quantifiers must not change matching behavior.
@@ -569,6 +584,25 @@ class TestConfigKeyRedosResistance:
         assert "Sup3rS3cret!" not in result
         assert ".password=" in result
 
+    def test_yaml_assign_redos_resistance(self):
+        """_YAML_ASSIGN_RE must not backtrack excessively on long inputs."""
+        import time
+
+        # 100 lines of a long dotted key with a secret keyword but no
+        # matching colon-value form — stresses the regex without matching.
+        line = "a." * 50 + "token not_an_assignment"
+        text = "\n".join([line] * 100)
+        t0 = time.perf_counter()
+        redact_sensitive_text(text)
+        assert time.perf_counter() - t0 < 2.0
+
+    def test_yaml_assign_secret_still_redacted(self):
+        # Possessive quantifiers must not change YAML matching behavior.
+        text = "spring.datasource.password: hunter2"
+        result = redact_sensitive_text(text)
+        assert "hunter2" not in result
+        assert "password:" in result
+
 
 class TestXaiToken:
     KEY = "xai-ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789abcdefghijklmnopqrstu"