fix(redact): add code_file param to skip false-positive ENV/JSON patterns

ENV-assignment and JSON-field regex patterns in redact_sensitive_text()
cause false positives when reading source code files:
- MAX_TOKENS=*** triggers the ENV assignment pattern
- "apiKey": "test" in test fixtures triggers the JSON field pattern

Add code_file=False parameter. When code_file=True, skip only the
ENV-assignment and JSON-field regex passes; all other patterns (prefixes,
auth headers, private keys, DB connstrings, JWTs, URL secrets) are
still applied.

Update file_tools.py (read_file and search_files) to pass code_file=True
so agent code analysis is not polluted by false-positive redactions.

Closes #15934

tools/file_tools.py

@@ -570,7 +570,7 @@ def read_file_tool(path: str, offset: int = 1, limit: int = 500, task_id: str =
 
         # ── Redact secrets (after guard check to skip oversized content) ──
         if result.content:
-            result.content = redact_sensitive_text(result.content)
+            result.content = redact_sensitive_text(result.content, code_file=True)
             result_dict["content"] = result.content
 
         # Large-file hint: if the file is big and the caller didn't ask
@@ -993,7 +993,7 @@ def search_tool(pattern: str, target: str = "content", path: str = ".",
         if hasattr(result, 'matches'):
             for m in result.matches:
                 if hasattr(m, 'content') and m.content:
-                    m.content = redact_sensitive_text(m.content)
+                    m.content = redact_sensitive_text(m.content, code_file=True)
         result_dict = result.to_dict()
 
         if count >= 3: