Bug: qfc-collection-navigation-digits-desync

[drmoisan]

• Work Mode: full-bug

Summary

QfcCollectionController.RegisterNavigation captures the side-effecting Digits property once,
while UnregisterNavigation re-evaluates it inside its loop. If the item count crosses the 10-item
boundary between the two calls, keys are unregistered under different names than they were
registered, leaving orphaned key registrations that later collide. This is the same failure family as
issue #232.

Environment

• OS/version: n/a (logic defect, reproducible wherever QuickFiler runs)
• Python version: n/a
• Command/flags used: n/a
• Data source or fixture: QuickFiler/Controllers/QfcCollectionController.cs

Steps to Reproduce

1. Inspect RegisterNavigation at QuickFiler/Controllers/QfcCollectionController.cs:1330-1341.
   Line 1332 captures the value once: var digits = Digits;, then passes that captured value to
   every RegisterNavigationAsyncAction call.
2. Inspect UnregisterNavigation at :1343-1356. Line 1347 re-evaluates Digits inside the
   loop, once per iteration.
3. Inspect the Digits property at :114-128. It reads _itemGroups?.Count live and returns 1 for
   counts below 10 and 2 at or above 10. It is side-effecting: it also drives
   SetVisualDigits via _digitRefreshNeeded.
4. Register navigation while the collection holds 10 or more items, so keys are registered as
   "01".."09".
5. Allow the item count to drop below 10 (for example by filing messages) before
   UnregisterNavigation runs.
6. UnregisterNavigation now computes digits == 1 and attempts to remove "1".."9".
7. KbdActions.Remove (QuickFiler/Controllers/KbdActions.cs:123-135) returns false silently
   when the key is absent; nothing surfaces the mismatch.
8. The original "01".."09" registrations remain. A later Add of the same key collides in
   KbdActions.Add (KbdActions.cs:90-98) and throws ArgumentException.

Expected Behavior

The digit width used to unregister a navigation key must be the same width used to register it, so
that every registered key is removed exactly once and no orphan remains.

Actual Behavior

When the count crosses the 10-item boundary between register and unregister, the removal silently
no-ops and the stale registrations persist until a later Add throws ArgumentException.

Logs / Screenshots

• Attached minimal logs or screenshot
• Snippet: Confirmed directly against source at QfcCollectionController.cs:1332 (single capture),
  :1347 (per-iteration re-evaluation), :114-128 (the live, side-effecting Digits property), and
  KbdActions.cs:123-135 (the silent false return). Discovered during preparation research for
  issue Feature: quickfiler-collection-controller-coverage #454 (epic Feature: quickfiler-80-per-file-coverage #136, child F11); full analysis in
  docs/features/active/2026-08-07-quickfiler-collection-controller-coverage-454/research/qfc-collection-controller.md
  section E14.

Impact / Severity

• Blocker
• High
• Medium
• Low

Produces a delayed, hard-to-attribute ArgumentException in keyboard registration rather than an
immediate failure at the point of the mismatch. Directly analogous to issue #232, which was a
navigation-key collision on page swap.

Source

From: docs/features/potential/2026-08-07-qfc-collection-navigation-digits-desync.md