Feature: quickfiler-item-controller-coverage #453

• Work Mode: full-feature

Problem / Why

Epic #136 requires every production .cs file compiled by QuickFiler/QuickFiler.csproj to reach
at least 80% line coverage and 75% branch coverage, or to sit on an explicitly ratified exemption
ledger. The QfcItemController partial-class family is one of the largest single clusters in that
denominator: 10 production partials plus one interface file, 3,180 lines in total.

The family is already substantially tested - 16 existing test files exist under
QuickFiler.Test/Controllers/ - so this is a gap-closure and exemption-removal exercise rather
than a build-from-zero effort. Four partials measured below the 80% line floor on the most recent
committed Cobertura report, and 19 method-level [ExcludeFromCodeCoverage] attributes across six
partials remove real production logic from instrumentation entirely.

Proposed Behavior

Raise every testable file in the QfcItemController family to at least 80% line and 75% branch
coverage, verified with the per-file coverage harness delivered by epic child F1, and remove every
[ExcludeFromCodeCoverage] attribute whose covered code can be reached through a seam. Retain an
attribute only where F1's ledger ratifies it as irreducible with a file-specific rationale.

No observable behavior change to QuickFiler flows. Testability refactors follow the epic's seam
hierarchy: interface seam, then injectable delegate, then adapter.

Acceptance Criteria

• Every testable file in scope reaches >= 80% line and >= 75% branch coverage.
• Every [ExcludeFromCodeCoverage] in scope is removed with the covered code tested, or
  retained only under an F1-ledger-ratified, file-specific rationale.
• No production file in scope exceeds 500 lines; any newly created file reaches >= 90% line
  coverage.
• Tests use MSTest, Moq, and FluentAssertions; deterministic, isolated, no temporary files,
  no external services, no live forms, no popups.
• Full C# toolchain green in final form; repository-wide coverage retained or improved.
• No behavior change to observable QuickFiler flows.

Constraints & Risks

• One partial-class family. All 10 partials declare the same type. The family is deliberately
  kept in a single epic child so no two children share a type or a test fixture.
• Sibling boundaries. ConversationResolver constructors belong to F4 (Feature: quickfiler-helper-classes-coverage #434) and are invoked
  positionally from this family. KeyboardHandler.cs belongs to F3 (Feature: quickfiler-keyboard-actions-coverage #430). IQfcDatamodel belongs
  to F5. Required upstream changes are recorded as cross-child contract notes, not sibling edits.
• State-transition invariants. Event wiring, navigation, and initialization carry ordering,
  re-entrancy, and dispose-before-setup invariants that must be covered explicitly.
• Determinism. Injected clock and fake timers only; Thread.Sleep, Task.Delay, and real
  wall-clock waits are prohibited in tests.
• Upstream dependency. F1 delivers the per-file coverage harness and the exemption ledger. A
  Phase 0 halt gate on those deliverables is required.
• Branch coverage is a separate gate. Line coverage at or above 80% does not imply branch
  coverage at or above 75%; both are reported independently.

Test Conditions

• Unit coverage of the four sub-floor partials: ViewerSetup, FocusAndTheme, MailActions,
  EventHandlers.
• Coverage of the 19 currently method-exempted members across six partials.
• Event-wiring subscribe/unsubscribe symmetry, re-entrancy, and idempotent dispose.
• Navigation state transitions and boundary conditions.
• Initialization ordering, including dispose-before-setup.
• Negative and error-handling paths for each covered member.

Source

From: docs/features/potential/2026-08-07-quickfiler-item-controller-coverage.md