Claude Haiku 5.5 (effort default (no --effort flag) · thinking on) on Ship settings format v3 that deployed v2 readers can still read (forward/backward compatibility, atomic save, idempotent migration)

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  "result": "`settings.py` now reads v1, v2, v3 and compatible newer files, and writes v3. It also has `migrate_dir(dir)` and an `UnsupportedVersion` class. `legacy_reader.py` is untouched. My test script passes: it checks that every file `save` writes is read correctly by the deployed `legacy_reader.read`. The script lives in `/tmp/f05-tests/`, outside the work tree.\n\nDecisions the spec didn't settle:\n\n- **Newer-file version info** is kept in `extra[\"top\"]` as `version` and `min_reader_version`, and only for files with version > 3. This keeps the in-memory shape the same for v1\u2013v3 loads. `save` pops those keys back out and writes them. Otherwise it writes v3 with `min_reader_version: 2`.\n- **`min_reader_version` > 3 on any file**, including a v3 file, raises `UnsupportedVersion`. The spec only stated this for newer files, but the same rule applies.\n- **`migrate_dir` checks first, then writes.** It reads and validates every pre-v3 file before writing anything. An invalid file therefore aborts the run with no changes. A `.bak` that differs from the file's bytes raises `FileExistsError`. An identical `.bak` is reused without being overwritten.\n- **`save` ignores unknown top-level keys in the input dict**, rather than raising. Unknown keys belong in `extra`, so silently dropping them is a tradeoff you may want to change.\n- **Atomic write** uses a random temp name created with `O_EXCL` and mode 0666 under the umask. If the target exists, its mode is copied. The temp file is removed on any failure.",
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