What's Changed

edit_replace: stale-context circuit breaker for consecutive invalid_params failures (#1132, closes #1118): After 5 consecutive not_found or ambiguous failures on the same (session_id, canonical_path) pair, edit_replace returns an EDIT_STALE_CONTEXT directive error instructing the model to re-read the file before retrying. The failure counter resets on any successful edit_replace or edit_overwrite on that path.

edit_replace: normalize CRLF to LF before matching (#1137): edit_replace_block now strips \r from both the file content and the old_text needle before attempting a match, so files with Windows line endings no longer produce spurious not_found failures.
validation: replace ancestor-walk with parent-dir validation in require_exists=false branch (#1136, closes #1134): The old ancestor-walk left canonical_base pointing at working_dir when no real ancestor was found, causing write_file_atomic to receive a malformed path and return an opaque internal_error. The new approach validates the immediate parent directory, rejects paths whose parent does not exist with a clear INVALID_PARAMS message, and aligns all "path is outside the allowed root" error messages to "path is outside the working directory".

exec_command: reframe cd prohibition as mechanical fact in tool description (#1133): Replaces the prohibition-style "Do not prepend cd to the command" with "Commands run inside working_dir; omit cd." -- grounding model behavior in stated runtime reality rather than a rule.

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