Claude Sonnet 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 newer-compatible files, and `save` writes v3. `migrate_dir` and `UnsupportedVersion` are in the same file. I ran a quick scratch script rather than a full test suite. It covered these cases:\n\n- **Legacy reader:** a saved v3 file, including one with `theme` set to `\"system\"`, is read by the unchanged `legacy_reader.py` and comes back as `\"light\"`. `legacy_reader.py` is untouched.\n- **Migration:** `migrate_dir` rewrote 2 old files and made a `.bak` for each. A second run returned 0.\n- **Newer files:** a v5 file with `min_reader_version` 3 loaded, kept its unknown keys in `extra`, and wrote back as v5 with those keys unchanged. A v5 file with `min_reader_version` 4 raised `UnsupportedVersion`.\n- **Validation:** `save` with a bad `font_size` raised `ValueError` and left no temporary file behind.\n\nI haven't tested the other validation rules (such as `quiet_hours` formats) or the case where a `.bak` already exists.\n\nI made three choices the spec doesn't spell out:\n- **Higher-version files:** `load` stores a higher file's `version` and `min_reader_version` in `extra[\"top\"]` so `save` can write them back. Files at v3 or below don't get these keys.\n- **Existing `.bak`:** if `<name>.json.bak` already exists, `migrate_dir` writes the backup to `.bak.1`, `.bak.2` and so on. It never overwrites one, and it never skips the backup.\n- **Bad files in a directory:** `migrate_dir` loads every file before rewriting any. If one file is invalid or unsupported, the error is raised and nothing in the directory is changed.",
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