feat: add Scient PDF reader

[yaacovcorcos]

User effect

Scient now opens PDFs directly in the side panel from the Files tree, file search, chat links, and other file-entry paths. The reader supports large files through byte-range loading, fast progressive search, selectable/copyable text, internal and safe external links, password-protected files, page navigation, 5% zoom controls, trackpad pinch zoom, thumbnails, outlines, and saving a copy.

This fixes the existing path where Files-tree selection treated PDFs as text and failed with WorkspaceBinaryFileError. The server's binary-file protection remains intact.

Architecture and upstream boundary

• Keeps the PDF experience in Scient-owned code under apps/web/src/scient/pdf.
• Uses narrow changes to T3-derived file-opening and preview seams; HTML and other browser-preview behavior remains unchanged.
• Uses exact, short-lived asset capabilities with GET, HEAD, and byte-range responses rather than broad workspace access.
• Pins PDF.js 6.2.108 and bundles its worker, support assets, and license locally.
• Preserves document view state when an expired capability is renewed and rejects stale capabilities when the underlying PDF changes.
• Restricts PDF-provided external links to HTTP(S) and routes them through the existing external-launch path.

Scope

• Base: 79835d70eed47265db46c950d6d07f0b5fd0dad1
• Head: d45a4e3dfdcab450c4921cd140e5f2969ff97cc5
• One feature commit; 35 files changed, 2,697 additions, 78 deletions.
• No OCR, Scient annotation system, cloud synchronization, or server binary-policy weakening.

Verification

• pnpm --filter @t3tools/web test: 237 files / 2,116 tests passed.
• Focused server asset/range suite: 3 files / 26 tests passed.
• Web typecheck, full lint, formatting check, git diff --check, and production web build passed.
• Production build contains the local PDF.js license and required support assets.
• The repository's full server typecheck continues to report pre-existing unrelated Effect diagnostics; the touched server behavior is covered by the focused passing tests above.

Yaacov manually exercised the reader, including a very large PDF, and confirmed the general reader and improved search behavior. This remains a draft pending final manual acceptance of the last keyboard-search navigation and PDF-only browser-button removal. No browser automation, screenshot comparison, geometry testing, visual-regression testing, or automated manual acceptance was performed.

Overlap and dependencies

This PR is independently mergeable from main. Draft PR #30 also touches FilePreviewPanel.tsx and docs/README.md for Markdown/HTML preview policy; the features are independent, but the later branch may need a small conflict resolution depending on merge order.

Rollback

Revert the single feature commit. Existing non-PDF file-opening paths and the server's binary-file protection remain available independently.

[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	11.3 KiB	11.3 KiB	+1 B (+0.0%)	15.1 KiB	✅
Codex	Thread snapshot wire	5.5 KiB	5.5 KiB	+1 B (+0.0%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	5.9 KiB	5.9 KiB	0 B (0.0%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	49.7 KiB	49.7 KiB	0 B (0.0%)	66.4 KiB	✅
Codex	Live turn messages	16	16	0 (0.0%)	21	✅
Claude	Total thread wire	11.4 KiB	11.3 KiB	−15 B (−0.1%)	15.1 KiB	✅
Claude	Thread snapshot wire	5.5 KiB	5.5 KiB	−1 B (−0.0%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	5.9 KiB	5.8 KiB	−14 B (−0.2%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	50.6 KiB	50.6 KiB	0 B (0.0%)	66.4 KiB	✅
Claude	Live turn messages	16	16	0 (0.0%)	21	✅

Baseline: 79835d7 · PR result: 047a069 · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 94.6 KiB
• Claude decoded thread snapshot: 95.4 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.