merge: align official T3 through f814983c

[yaacovcorcos]

What Changed

• align the complete official T3 range from 6c583620ff7ad3235b135af7107c0543467eecfa through f814983c262b42bd79247bae377a709925c70d63 with literal upstream ancestry
• add multiple pull-request links, linked-thread search, GitHub stack actions, persisted PR read caching, model bulk controls, expanded-image zoom/pan, preview-to-PiP, diff palettes, and the remaining desktop/mobile fixes in the range
• preserve Scient provider lifecycle, rich Markdown, conversation forks, pending-save protection, explicit MCP capabilities, retired-projectless compatibility, product identity, and release/publication boundaries
• register T3's colliding multi-PR migration as Scient migration 53, preserving immutable migrations 50–52 and existing databases

Why

This is the next full bounded upstream alignment. The merge keeps all 23 upstream commits as ancestry while composing Scient-owned policy at narrow seams. Migration 53 prevents the new table from being silently skipped on databases whose migration ledger has already advanced past T3's original migration number.

Verification

• pnpm exec vp fmt --check
• pnpm exec vp lint --report-unused-disable-directives
• pnpm run typecheck
• VITEST_MAX_WORKERS=2 pnpm run test
• pnpm run build
• pnpm run test:desktop-smoke
• pnpm run brand:check
• pnpm knip:check
• pnpm release:smoke
• Scient analysis, onboarding, Skills, and LaTeX seam checks
• exact-parent upstream provenance check
• synthetic migration compatibility tests from migrations 49, retired 50, and 52
• isolated clean-state desktop review app

The full suite passed, including 7,017 web tests and 6,391 server tests. Mobile native static checks completed; SwiftLint, ktlint, and detekt were unavailable and therefore explicitly skipped. No release or publication was performed.

Documentation Impact

Documentation impact: Updated — UPSTREAM.md, upstream-state.json, docs/internals/2026-09-10-upstream-sync-f814983c.md, and source-control/glossary/architecture documentation.

UI Changes

The alignment includes upstream UI behavior for multi-PR surfaces and stacks, model bulk controls, expanded-image zoom/pan, preview-to-PiP, diff palettes, PR actions, settled-thread presentation, and mobile glass/list fixes. Owner manual review was performed in the isolated candidate before delivery.

Checklist

• This PR is one complete bounded upstream alignment
• I explained what changed and why
• Scient-owned behavior and publication boundaries were reviewed
• Automated qualification and isolated manual review were completed

Implemented and reviewed by GPT-5 through the Codex desktop harness.

[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	13.5 KiB	13.5 KiB	−6 B (−0.0%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.1 KiB	7.1 KiB	+3 B (+0.0%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.4 KiB	6.4 KiB	−9 B (−0.1%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	56.2 KiB	56.2 KiB	0 B (0.0%)	66.4 KiB	✅
Codex	Live turn messages	8	8	0 (0.0%)	21	✅
Claude	Total thread wire	13.6 KiB	13.6 KiB	+20 B (+0.1%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.1 KiB	7.1 KiB	+8 B (+0.1%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.5 KiB	6.5 KiB	+12 B (+0.2%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	57.8 KiB	57.8 KiB	0 B (0.0%)	66.4 KiB	✅
Claude	Live turn messages	8	8	0 (0.0%)	21	✅

Baseline: 7cefb60 · PR result: 5a70ed5 · 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: 114.1 KiB
• Claude decoded thread snapshot: 114.7 KiB

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