fix(engine): preserve step progress + worktree across internal task bounces

Workflow-step REVISE retries, pause→todo handoffs, and the
context-overflow fresh-session requeue were all routing tasks back to
`todo` before returning to `in-progress`. The default reopen-to-todo
path reset every step to pending and rewrote PROMPT.md checkboxes, so
each retry restarted from step 0 even when earlier steps had already
been done — the symptom seen on FN-2978, where every workflow REVISE
or pause cycle wiped the task's progress.

- Add `preserveResumeState` to `TaskStore.moveTask`. When set, skip
  `resetAllStepsToPending` + `resetPromptCheckboxes` and keep
  `worktree` and `executionStartedAt` so the resumed run reattaches to
  the same checkout. `status`, `error`, and `blockedBy` still clear.
- Use it on the workflow-rerun bounce, the three pause-graceful
  handoffs, and the context-overflow requeue. The agent-terminated
  pause path still discards (it nukes worktree+branch by design).
- Context-overflow requeue clears `sessionFile` synchronously in the
  awaited `updateTask` immediately before `moveTask`, so the next
  dispatch cannot reopen the saturated session via a stale pointer.
- `fn_task_update` no longer silently regresses `done`/`skipped` steps
  to `in-progress`, no longer captures a stale rewind checkpoint when
  it does, and tells the agent honestly when a regression is ignored.
- Mobile chat keyboard: ChatView/QuickChatFAB gate layout on the new
  `keyboardOpen` flag so focused-input + viewport-shrink iOS cases
  still adjust when the computed overlap is zero.

Tests:
- New `preserveResumeState` coverage in store.test.ts; updated
  workflow-rerun + pause-graceful assertions in executor.test.ts.
- Restructured the previously-flaky "routes exhausted prompt-mode
  workflow hard failures" test to drive the bounce inline; passes in
  isolation and in the wider workflow/pause/context sweep (59/59).
- Added regression tests in ChatView.test.tsx and QuickChatFAB.test.tsx
  for the iOS last-resort `keyboardOpen=true, keyboardOverlap=0` case.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/dashboard/app/components/ChatView.tsx

@@ -759,12 +759,12 @@ export function ChatView({ projectId, addToast }: ChatViewProps) {
   const mentionCursorPosRef = useRef(0);
   const mode = useViewportMode();
   const isMobile = mode === "mobile";
-  const { keyboardOverlap, viewportHeight } = useMobileKeyboard({
+  const { keyboardOverlap, viewportHeight, keyboardOpen } = useMobileKeyboard({
     enabled: isMobile && !!activeSession,
   });
 
   const threadKeyboardStyle: CSSProperties =
-    keyboardOverlap > 0
+    keyboardOpen
       ? ({
           "--keyboard-overlap": `${keyboardOverlap}px`,
           ...(viewportHeight !== null ? { "--vv-height": `${viewportHeight}px` } : {}),