Fix breadcrumb bridge keyboard-navigation defects: Enter-key binding, scroll-into-view, and #440 router-test coverage gap

[drmoisan]

Fix breadcrumb bridge keyboard-navigation defects: Enter-key binding, scroll-into-view, and #440 router-test coverage gap

Summary

• Adds an Enter key branch to the breadcrumb WebView2 bridge's inline JS keydown map, posting { type: 'rowSelected', rowId: id } so keyboard-only users can commit a highlighted suggestion (Finding 2, source Bug: efc-enter-activates-valid-highlighted-suggestion #641).
• Adds scroll-into-view logic to the same bridge's inbound message listener so arrow-key navigation keeps the selected row visible after a render/subfolderResult DOM update (Finding 1, source Bug: efc-keyboard-navigation-keeps-highlighted-row-visible #640).
• Adds a new MSTest regression test asserting both JS behaviors are present in the BreadcrumbDocumentAssets.BridgeJs constant, following this repo's existing string-containment precedent for JS content with no headless-browser harness.
• Closes a router-test coverage gap in FolderBreadcrumbBridgeRouterTests.Route_LeftArrow_NothingToCollapse_ReportsUnhandledLeft: the test previously discarded the results of its first two Arrange-phase ArrowAsync calls; it now asserts each parses to a RenderMessage, preserving the Bug: breadcrumb-left-right-arrow-parent-child-navigation #440 ancestor-walk contract (two presses to reach root, UnhandledArrowMessage only on the third) (Finding 3, source Bug: breadcrumb-router-test-cr1-defect-neutral #693).
• No production wire-format, message-type, or router-case change is introduced; the Enter binding reuses the existing rowSelected/SelectRow infrastructure.
• Full C# toolchain (CSharpier format/check, analyzer rebuild, nullable rebuild, vstest with coverage) passes cleanly in a single pass; repository-wide coverage is unchanged or improved (85.39% line-rate, 79.46% branch-rate), and the sole modified production file contributes zero new coverable lines (const-string-only edits).

Why

A code-review sweep of the breadcrumb WebView2 keyboard-bridge path found three related gaps, grouped into one issue because all three touch the same keyboard-routing path from WebView2 through to FolderBreadcrumbBridgeRouter: the inline JS keydown map was missing an Enter binding entirely, arrow-key navigation had no scroll-into-view feedback, and a router test masked a left-arrow collapse coverage gap by discarding two of its own Arrange-phase results. Findings 1 and 2 share a root cause: the inline JS keydown map in BreadcrumbDocumentAssets.cs was built out incrementally (arrow keys first) and was never extended with an Enter branch or scroll-into-view logic. Finding 3 is an unrelated test-coverage gap found during the same review pass. Full details are recorded in docs/features/active/2026-09-02-breadcrumb-bridge-keyboard-navigation-defects-737/issue.md and spec.md.

What Changed

Core feature (production):

• UtilitiesCS/OutlookObjects/Folder/BreadcrumbDocumentAssets.cs — two additive insertions to the BridgeJs JS constant: (1) an Enter branch in the keydown listener that looks up the .rowwrap.selected element and posts { type: 'rowSelected', rowId: id }, mirroring the existing arrow-key handler's lookup pattern; (2) a scroll-into-view call (scrollTarget.scrollIntoView({ block: 'nearest' })) added to the inbound render/subfolderResult message listener.

Tests:

• UtilitiesCS.Test/OutlookObjects/Folder/BreadcrumbHtmlRendererTests.cs — new [TestMethod] Issue737BridgeJsPostsRowSelectedOnEnterAndScrollsSelectedRowIntoView, asserting the BridgeJs constant contains the Enter-key branch and the scroll-into-view call, following the existing Issue439... string-containment precedent.
• UtilitiesCS.Test/OutlookObjects/Folder/FolderBreadcrumbBridgeRouterTests.cs — Route_LeftArrow_NothingToCollapse_ReportsUnhandledLeft now captures and asserts both previously-discarded ArrowAsync(router, "left") Arrange-phase results as RenderMessage, in addition to the pre-existing third-press UnhandledArrowMessage assertion. No helper method (ArrowAsync, PopulatedRouterAsync) or provider-mock factory was modified.

Docs/evidence:

• docs/features/active/2026-09-02-breadcrumb-bridge-keyboard-navigation-defects-737/ — issue, spec, research, atomic plan, policy-audit, code-review, feature-audit, and full baseline/QA-gate evidence trail (Phase 0 through Phase 5).

Architecture / How It Fits Together

The breadcrumb bridge is a WebView2-hosted inline-JS component (BridgeJs, defined as a C# string constant in BreadcrumbDocumentAssets.cs) that posts messages to the host via window.chrome.webview.postMessage. The C# side (FolderBreadcrumbBridgeRouter) already recognizes and handles rowSelected messages from the existing mouse-click path; the new Enter-key branch reuses that same message shape and C#-side handling, so no new message type, codec branch, or router case is required. The scroll-into-view addition is a pure client-side DOM operation inside the same inbound message listener that already re-renders the document on render/subfolderResult; it has no C#-side counterpart. The router-test fix (FolderBreadcrumbBridgeRouterTests.cs) is test-only and does not touch QuickFiler/Controllers/BreadcrumbBridgeRouter.Arrows.cs (the #440 production logic) or any Qfc-pipeline file.

Verification

Completed (see docs/features/active/2026-09-02-breadcrumb-bridge-keyboard-navigation-defects-737/evidence/ for full artifacts):

• CSharpier format (scoped to the Write Set) and repo-wide CSharpier check: exit 0.
• .NET analyzer rebuild (-EnableNETAnalyzers -EnforceCodeStyleInBuild): exit 0.
• Nullable rebuild (-TreatWarningsAsErrors): exit 0.
• Scoped vstest run covering every touched/added test (FolderBreadcrumbBridgeRouterTests, FolderBreadcrumbBridgeRouterInFlightTests, BreadcrumbHtmlRendererTests): 41 total, 0 failed.
• New/modified tests run in isolation: Issue737BridgeJsPostsRowSelectedOnEnterAndScrollsSelectedRowIntoView (1 passed), Route_LeftArrow_NothingToCollapse_ReportsUnhandledLeft (1 passed), and the sibling Bug: breadcrumb-left-right-arrow-parent-child-navigation #440 regression test ArrowAsync_QfcLeftOnMultiSegmentRow_RoutesParentSelectTransition (1 passed) to confirm consistency with the Bug: breadcrumb-left-right-arrow-parent-child-navigation #440 ancestor-walk contract.
• Full-repository coverage capture: line-rate 85.3867%, branch-rate 79.4649% (both clear the repo's 85%/75% floors); the modified production file (BreadcrumbDocumentAssets.cs) is const-string-only and contributes zero new coverable lines, so the coverage delta reflects no regression on changed lines.
• Independent feature-review pass (policy-audit, code-review, feature-audit) found 0 blocking findings; all 7 acceptance criteria independently re-verified against the diff and evidence, not just the executor's checkbox state.

Recommended: CI re-run of the full C# toolchain against the merge commit, as with any other PR in this repository.

Backward Compatibility / Migration Notes

No breaking changes. No public API, message-wire-format, or router-contract change. No renamed or removed paths.

Risks and Mitigations

• Risk: The new Enter-key branch could interact unexpectedly with the existing arrow-key selection state. Mitigation: The branch reuses the identical .rowwrap.selected lookup and rowSelected post shape the mouse-click path already uses; no new C#-side handling was introduced, so existing rowSelected handling coverage applies unchanged.
• Risk: The scroll-into-view call could fire when no row is selected. Mitigation: The call is guarded by an if (scrollTarget) check; it is a no-op when .rowwrap.selected does not resolve to an element.
• Risk: The router-test fix could mask or alter the Bug: breadcrumb-left-right-arrow-parent-child-navigation #440 fix's behavior. Mitigation: The fix is test-only (no production code touched) and the sibling Bug: breadcrumb-left-right-arrow-parent-child-navigation #440 regression test was independently re-run and passed, confirming the ancestor-walk contract is unaffected.

Review Guide

Suggested order:

1. UtilitiesCS/OutlookObjects/Folder/BreadcrumbDocumentAssets.cs — the two production JS insertions (Enter branch, scroll-into-view).
2. UtilitiesCS.Test/OutlookObjects/Folder/BreadcrumbHtmlRendererTests.cs — the new string-containment test.
3. UtilitiesCS.Test/OutlookObjects/Folder/FolderBreadcrumbBridgeRouterTests.cs — the router-test assertion fix.
4. docs/features/active/2026-09-02-breadcrumb-bridge-keyboard-navigation-defects-737/ — issue/spec/plan/evidence, for traceability only.

No mechanical moves, renames, or large generated diffs are present; the change is small and self-contained.

Follow-ups

None. Issue #737 (all three consolidated findings) is fully resolved by this change.

• Closes Bug: breadcrumb-bridge-keyboard-navigation-defects #737