Backlog: O4 done, O10 added 13a0f400dff9

- [x] O1 Property tests (proptest) that applying the same changes in any order gives the same state, over random edit sequences on several files.

- [x] O2 `oxy fsck`: verify every object's hash, every change's references and signatures, the op log chain, and report precisely.

- [x] O3 Crash safety audit: every write goes through write_atomic or the store's batch; a test that interrupts commit and push at each step and proves the repository still opens and fscks.

- [ ] O5 Concurrency: two processes committing, snapshotting and pushing on one repository; locks hold, nothing is lost.

- [ ] O6 Error messages audit: every user-facing error says what to do next; `oxy doctor` checks identity, config, remotes, CA files, hub reachability.

- [ ] O7 Shell completions (`oxy completions bash|zsh|fish`) and man pages generated from clap.

- 2026-09-28 V1 done: hub API `GET /proposals/{n}/files` and `/proposals/{n}/content/{base|head}/{path}`, and anchored comments now carry their current `line` (deployed). oxygenhub-vscode 0.2.0: proposals expand to files, native diff editor per file, View Changes multi-diff, review threads on the projected side; installed in Default and Rust profiles (Developer: Reload Window to pick it up). Tests: hub api test extended; extension pass 6 fail 0 against a real hub.

- 2026-09-28 O3 done: new `oxy_core::durable` (unique temp, fsync, rename, directory fsync) for every durable write; **real bug fixed**: inside a write batch the op head moved before the batch (including the new op object) was on disk, so a crash there left an unopenable repository; `Store::flush` now runs before the head moves. Test stops commit (20 steps) and push (32 steps) at every step: both repos open, fsck clean, command retries. Spec §13.6. Hub rebuilt and redeployed with the fix. Not covered: working-copy file writes during checkout are still plain writes (user files, recoverable by snapshot).

- 2026-09-28 H3 done: header theme switch (dark/light/auto) and Settings → Appearance, theme cookie; auto follows the system live. Light-mode pass by headless Chrome screenshots of dashboard, overview, file, proposal, issue, settings, changes: found and fixed highlighted code drawing boxes in both themes (syntect scope `comment` colliding with the page `.comment` class; classes now `sy-` prefixed) and the band ADMIN link unreadable in light. Test `theme_is_chosen_in_settings_and_remembered_in_a_cookie`; hub spec §6.1; deployed. The code editor picks its theme at load, not live.