Improves PDF tagging detection

[srkirkland]

Improves PDF tagging detection by treating PDFs with trivially tagged structures as broken. This forces re-tagging to ensure proper accessibility.

Summary by CodeRabbit

• Bug Fixes

  • Improved detection of inadequately tagged PDFs to trigger automatic re-tagging when needed
  • Ensured document titles are properly displayed in PDF viewer title bars

• Tests

  • Added integration tests to verify correct handling of trivially tagged PDFs and title display settings

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📝 Walkthrough

Walkthrough

This PR adds heuristics to detect effectively empty tag trees in PDFs and force re-tagging when detected, updates viewer preferences to display document titles in PDF viewers, and adds corresponding integration tests to verify these behaviors.

Changes

Cohort / File(s)	Summary
Tag Tree Detection server.core/Ingest/PdfProcessor.cs	Introduces TagTreeHasContentItems and Dereference helpers to detect effectively empty tag trees. Modifies ReadSourcePdfInfo to return TaggedBroken when tag tree root content is absent, forcing re-tagging of such PDFs.
Title Display Preference server.core/Remediate/PdfRemediationProcessor.cs	Adds EnsurePdfDisplaysTitleInTitleBar helper to update PDF catalog's DisplayDocTitle viewer preference. Integrates into EnsurePdfHasTitleAsync at three points to ensure title bar consistency with document title.
Tag Tree Detection Tests tests/server.tests/Integration/Ingest/PdfProcessorIntegrationTests.cs	Adds ProcessAsync_WithAdobeEnabledAndTriviallyTaggedPdf_Autotags integration test and CreateTriviallyTaggedPdf helper to verify trivially tagged PDFs trigger autotagging when Adobe services enabled.
Title Display Verification tests/server.tests/Integration/Remediate/PdfRemediationProcessorTitleTests.cs	Introduces GetDisplayDocTitle test helper to inspect PDF catalog viewer preferences for DisplayDocTitle flag and verify it is enabled in remediated outputs across multiple tests.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~22 minutes

Possibly related PRs

• table and lang, plus only tag when needed #26: Extends tag-tree detection and tagging-state logic in ReadSourcePdfInfo that were introduced in that PR.
• Enhances PDF accessibility with alt text and titles #7: Modifies the same PDF ingest/remediation components and directly touches viewer preference flows from that PR.

Poem

🐰 Tags so empty, we'd hop right past,
Now we find them and fix them fast!
Titles bright in the viewer's sight,
PDFs tagged and displayed just right! 📄✨

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 11.76% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'Improves PDF tagging detection' accurately summarizes the main change: detecting effectively empty tag trees and treating them as broken to force re-tagging. This is the primary objective addressed across the core logic changes.

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch srk/tweaks

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