fix: add keyboard-equivalent treemap navigation

[seonghobae]

Purpose

Make the disk treemap operable and understandable without a pointing device while preserving the existing pointer visualization and navigation authority. The native equivalent now remains keyboard-scrollable even when a folder contains only files and tells the customer what to do when no entries are available.

Exact current state

• Exact source head: d2bf5e5d2344bb33327491c16862031c4a7daa20.
• Live protected main: be418bac9bfbdc8aa41b1a698713833e3dbccfdc.
• The PR is open, Ready for review, mergeable, and based directly on protected main.
• Current semantic delta remains exactly src/lib/Treemap.svelte plus src/lib/treemapAccessibilityContract.test.ts.
• Current-head formal reviews and review threads are empty; no approval is claimed.

Test-first accessibility repair

• RED head 0ac1b50d4634c18e5d9de55d0d10c4fceed09ab4 required a native keyboard-equivalent surface while protected main exposed navigation only through the pointer canvas.
• Initial implementation 3fde380f7b7df0f68b8e049a32563c6fd03822d4 kept treemap drawing/click geometry unchanged, marked the pointer canvas assistive-technology-hidden, and added a native <details>/list alternative over the same node.entries with normal directory buttons invoking only onOpen(entry.path).
• Review then found that the alternative list itself had a 14rem overflow boundary but no sequential focus target when a folder contained files only, and an empty node rendered a blank list without a next action.
• Test-only commit 72c262a53b2aa3156d19a4bad3c3f085b723fcce requires a named focusable overflow region, visible keyboard focus, action-oriented directory labels, an entry count, and an empty-state recovery instruction.
• Current implementation d2bf5e5d2344bb33327491c16862031c4a7daa20 moves overflow to a role="region", tabindex="0" wrapper, adds a focus-visible outline, labels directory rows as 폴더 열기, reports the entry count in the native summary, and tells the customer to move to the parent folder or scan another folder when no entries exist.

Scan data, path authority, filesystem mutation, treemap geometry, pointer navigation, and directory-open authority remain unchanged. File entries remain descriptive rather than becoming mutation controls.

Standards boundary

This is a narrow WCAG 2.2 non-text-content and keyboard-operability repair using native HTML controls and a named scroll region rather than synthetic canvas keyboard behavior.

Exact-head validation

For exact head d2bf5e5d2344bb33327491c16862031c4a7daa20:

• Test 31885078411 — queued;
• Release 31885078364 — pending;
• Security Scan 31885078282 — queued;
• SAST Semgrep 31885078288 — queued.

Queued or pending evidence is not passing, and predecessor-head success does not transfer. Conditional PR-inapplicable publication or attestation helpers are not represented as passing release or provenance evidence.

Scope / non-duplication

This line owns only src/lib/Treemap.svelte and its focused accessibility contract. It does not modify src/routes/+page.svelte owned by #202, TopFiles #203, repository-wide exact coverage #156, canonical documentation #149, or any cleanup/cloud/provider authority line.

Remaining integration blockers

• The live organization ruleset requires one independent approving review, approval after the last push, and review-thread resolution; the current head has no approval.
• Repository-wide exact 100% owned-production region/statement-equivalent, branch, function, and line coverage remains materially unsatisfied on canonical owner ci: require exact-head production coverage evidence #156.
• Ready-for-review status is not merge authorization.

Required before merge

Do not merge unless the unchanged exact head satisfies every applicable live required workflow and current finding, every review thread is resolved, a qualifying independent approval covers the last push/current head, fresh protected-main ancestry remains current, the live review ruleset is satisfied, and repository-wide exact coverage is satisfied without exclusions or threshold weakening. Pending, queued, skipped-required, neutral-required, failed, stale, predecessor, synthetic, diagnostic-only, status-only, model-only, rate-limited, no-source scanner, or infrastructure-only evidence is not passing.

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Review details

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 53828270-f176-4a32-a65b-565dcef2d78b

📥 Commits

Reviewing files that changed from the base of the PR and between be418ba and d2bf5e5.

📒 Files selected for processing (2)

• src/lib/Treemap.svelte
• src/lib/treemapAccessibilityContract.test.ts

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[seonghobae]

Closing this line as stale/duplicative against the current product composition rather than merging a second navigation authority.

On live main (be418bac9bfbdc8aa41b1a698713833e3dbccfdc), src/routes/+page.svelte already renders the same node.entries immediately after <Treemap> as the canonical native <ul class="entries">; directories are native buttons that call the same open(e.path) path-navigation authority. This PR's current head d2bf5e5d2344bb33327491c16862031c4a7daa20 adds another complete list and another set of directory controls over that same collection, so merging it would duplicate semantics/actions and create two UI authorities.

The remaining narrow concern—keyboard scrolling when the canonical list contains only non-focusable file rows—belongs with the existing .entries surface in src/routes/+page.svelte, which is currently owned by #202, not with a second list inside Treemap.svelte. That should be repaired test-first on the canonical surface after the active owner is stable. Current-head Test/Release/Security/SAST are green, but those checks do not make a redundant UI change desirable or merge-authorized.