test(rtl): add generated Arabic fixtures guarding visual-order extraction

[mathurshubham]

Implements #218: Arabic/RTL regression coverage with fixtures generated at test time — no hosted sample files, no licensing question, and no headless-Chrome dependency in CI.

Why now

#440 just landed geometric visual-order reversal in fix_visual_order_rtl. As #218 points out, RTL bugs are uniquely prone to silent regression: the output looks like text to a reviewer who doesn't read the script, so a revert or refactor that breaks it is invisible in a diff. These tests are the guard.

How the fixtures are generated

Pure Rust, in-test (tests/rtl_generated_tests.rs, no production source touched). make_rtl_pdf(lines, storage) hand-builds a single-page PDF with a byte-accurate xref — the same pattern as the repo's existing make_text_pdf helpers and the same shape as the Hebrew fixtures that landed with #440:

• A /TrueType font with a /ToUnicode CMap maps single-byte codes to Unicode, so no real Arabic glyph program is embedded.
• Each token is one Tj with an absolute Tm. Visual-order storage reverses each Arabic run's characters and paints left-to-right (increasing x — the case fix(extract): reverse visual-order RTL text using glyph geometry #440 must reverse). Logical-order storage stores reading order and paints right-to-left (the case fix(extract): reverse visual-order RTL text using glyph geometry #440 must leave alone). Both the geometric vote and restore_embedded_ltr_runs are exercised.
• Every test word carries a lam-alef pair emitted as a single glyph code mapping to two code points (U+0644 U+0627), covering the multi-character ToUnicode expansion where naive reversal breaks.

Assertions (from #218)

1. Digit groups survive reordering intact — 126,248.34 inside an Arabic line must come out unreversed: arabic_visual_order_keeps_digit_group_intact, arabic_logical_order_keeps_digit_group_intact, arabic_digit_group_intact_in_positioned_items.
2. Multi-char ToUnicode ligature round-trip — arabic_visual_order_ligature_round_trip, arabic_logical_order_ligature_round_trip.
3. Negative control — the character-reversed corruptions (مالسلا, مالكلا) must be absent from output: visual_order_negative_control_wrong_output_is_rejected.

Plus visual_and_logical_storage_agree: both storage conventions extract to identical reading order. Both process_pdf_mem (markdown) and extract_text_with_positions_mem (positioned items) are covered.

Revert check

With fix_visual_order_rtl temporarily neutralized (early return), the 4 visual-order tests fail with the expected reversed corruption (e.g. ## لالخ مالسلا مالكلا) while the 3 logical-order/positioned tests still pass — exactly the split the guard should produce. All 7 pass on current main.

Verification

Full cargo test green (1015 lib + 165 integration + 7 new rtl_generated + 3 bin + 2 doc-tests, 0 failures); cargo fmt and cargo clippy -- -D warnings clean.

Out of scope, per the issue discussion: the synthetic wrong-ToUnicode corruption generator (that targets #214's detection feature, not this reversal guard) and Arabic-Indic digit variants (the ASCII digit-group case from the issue is asserted; #440's logic covers both scripts).

Closes #218.

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Summary by cubic

Adds generated Arabic/RTL regression tests that synthesize PDFs at test time to guard visual-order text extraction. Prevents silent regressions in fix_visual_order_rtl (#440) without hosting sample files or adding headless browser deps. Closes #218.

• Review notes
  • Test-only change: new tests/rtl_generated_tests.rs builds single-page PDFs in Rust with a /ToUnicode CMap; exercises both visual and logical storage and restore_embedded_ltr_runs.
  • Assertions per Add RTL/Arabic regression fixtures to CI — generated at test time, nothing to host #218: digit groups (126,248.34) remain unreversed inside RTL lines; lam‑alef (لا) multi-character ToUnicode expansion round-trips; negative control rejects raw reversed forms; both process_pdf_mem and extract_text_with_positions_mem agree; visual and logical storage extract to identical reading order.
  • Guard verified: disabling fix_visual_order_rtl makes visual-order tests fail while logical/positioned tests pass.

^{Written for commit f856f3f. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 1 file

<sub>Shadow auto-approve: would auto-approve. Adds generated Arabic/RTL regression tests to guard visual-order text extraction logic. This test-only change synthesizes PDFs in-memory to verify digit preservation and ligature handling without modifying production code.

Re-trigger cubic</sub>