security: block Unicode dot homoglyph hidden-file bypasses

[seonghobae]

Security defect

The hidden-file gate recognized only ASCII .. Names beginning with U+3002, U+FF0E, or U+FF61 could therefore reach generated directory indexes even though they are visually confusable dot-prefixed sensitive files.

Test-first evidence

The branch began with a production-shaped RED regression: HiddenFileSecurityTest created each confusable-dot filename and required process_ignore_file to classify it as hidden. The failure occurred at the product assertion on protected-base production code, not during fixture setup. A follow-up test commit strengthened the classifier contract for ASCII ., all three evidenced Unicode dot confusables, ordinary visible names, and the empty-string boundary before the production repair.

Repair

String.isHiddenFile() now owns hidden-prefix classification and recognizes ., U+3002, U+FF0E, and U+FF61. The same classifier is used consistently by ignore-file generation, recursive traversal, and directory rendering, preserving the existing ASCII-dot behavior while preventing the homoglyph bypass at every entry path.

Exact-head proof

Exact head 847c85b8780e5f4e4b996e8f45d6df3e6e8690c0 is mergeable against protected base f4038883078262be061a9a525350b71fa0293bbd and has completed hosted validation successfully:

• CI run 31295839694: success;
• SAST Semgrep run 31295839692: success;
• Security Scan run 31295839697: success.

No inline review threads or formal reviews exist at this exact head yet; draft status is being removed only after the production repair and exact-head gates are green so independent review can run on the maintained candidate.

Duplicate consolidation

This PR consolidates the stronger regression coverage from duplicate security reports #382 and #391 onto current master ancestry. Those older branches should not be merged independently once this maintained exact-head repair is accepted.

Merge contract

Do not merge unless the unchanged exact head satisfies every repository-required CI/security/review gate, has zero valid unresolved findings, and has qualifying independent non-author approval where repository policy requires it. Do not bypass branch protection or weaken tests.

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Review details

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📥 Commits

Reviewing files that changed from the base of the PR and between f403888 and 847c85b.

📒 Files selected for processing (2)

• src/main/kotlin/html4tree/main.kt
• src/test/kotlin/html4tree/HiddenFileSecurityTest.kt

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