[Cordedmink2]

Why

If you get distracted partway through a focus round, the only options today are to keep going with less time than you meant to spend, or restart the round and lose your progress. This adds a small +1 min control so you can give time back to the current round.

What changes

• Engine: a new TimerCommand::Rewind { secs } moves the elapsed position backwards, never below 0. The round's total duration, type and running/paused state stay the same. The dial arc and the MM:SS readout are both computed from the same elapsed_secs and total_secs, so they stay in sync.
  • Running: the tick timeline is re-anchored at the last tick boundary, so the countdown continues from the new position with no drift and no burst of catch-up ticks.
  • Paused or suspended: the timer stays paused. Rewinding all the way to 0 puts the engine back to Idle and emits Reset, the same result as Restart Round, so the toggle, tray and UI all agree the round hasn't started.
  • Idle: the command is ignored.
• Small robustness fix: when the engine is Paused and receives Start, it now resumes instead of silently dropping the command. The controller sends Start whenever the shared elapsed position is 0, which can happen if a running round is rewound to 0:00 and then paused.
• Plumbing: a new timer_rewind IPC command and timer:rewound Tauri event. The tray arc redraws immediately. There is also an additive rewound WebSocket broadcast ({ "type": "rewound", "payload": { "elapsed_secs", "total_secs" } }), so overlays don't drift. Existing message formats are unchanged.
• UI: a "+1 min" text button sits inside the dial, just below the readout.
  • It has a tooltip, an accessible label and a minimum 24px target, and works with Tab and Enter/Space.
  • It is disabled when nothing has elapsed and hidden in compact mode, so the dial-only layout is unchanged.
  • No other controls moved.
• Strings for all 8 locales.

Relationship to #517

#517 also proposes extending the current round (+5) as part of a larger redesign: a distraction counter, sub-minute breaks and a control layout change. This PR is deliberately narrower. It adds one control, leaves the layout alone and doesn't change any settings. If you'd rather take #517's approach, I'm happy to close this.

Verification

• cargo test: 96 passed, 0 failed. This includes 7 new event-synchronised engine tests:

  • rewind while running
  • clamp at 0 while running
  • rewind while paused, then resume
  • paused rewind to 0 → Idle
  • idle no-op
  • zero-second no-op
  • Start while paused resumes

  The timer tests passed 15 times in a row. I also checked the tests themselves: removing the timeline re-anchor makes 2 of them fail.

• cargo clippy -- -D warnings: clean.

• npm run check: 0 errors, 0 warnings. prettier --check is clean on the changed frontend files.

• The real Svelte main window was driven in headless Chromium against a mocked Tauri IPC that mirrors the engine's semantics (15/15 checks):

  • The button is disabled when idle.
  • Clicking it sends timer_rewind { secs: 60 }.
  • The readout and the arc's stroke-dashoffset stay consistent after rewinding while running, rewinding while paused, and on later ticks.
  • It clamps at the full duration.
  • Keyboard activation works.
  • The button is hidden in compact mode.
  • No console errors.

  I checked the layout at 300×400, 360×478 and 500×600: the button doesn't overlap the readout and stays inside the ring.

• Builds and tests ran on Linux (aarch64, Rust stable in a Debian bookworm container). I haven't run it natively on macOS or Windows; the changes are platform-neutral.