fix(web): keybinding rows, nested markdown images, composer spacing, project picker

[rynfar]

Four change sets from the f94a0d646..1f8ed54ad T3 upstream review. Three cherry-picks and one cherry-pick with adaptation.

• #8627 (074bcd6dc) — the sidebar project picker popup stays inside the sidebar (min-w-0 overflow-hidden on the combobox popup and picker shell). Byte-identical to upstream; follow-up to #5931, already adopted.
• #8501 (c0e09f323) — markdown file previews resolve relative images from the file's directory instead of the project root; Windows drive paths, SVG fragments on signed URLs, and authored width/height/alignment are preserved; copy yields the authored markdown. Byte-identical; Pylon's workspaceRelativePath and editor-label divergence in markdown-links.ts / ChatMarkdown.tsx are untouched.
• #8532 (be218ac76) — the keybindings settings page becomes SettingsRow items instead of the four-column table that forced a 680px horizontal scroll. Upstream's file taken verbatim except the two product strings, which say Pylon.
• #8090 (660cddd3b) — four composer spacing defects, all verified present in Pylon: the scroll-to-end pill now ignores the shoulder-tab reserve unless a tab is present; the draft hero reduces its bottom padding when a tab is present; shoulder tabs inset to match the composer corner; and task segment bars hide past 10 steps.

The one adaptation

Upstream caps segment bars in its TaskSegments helper. Pylon renders segments through its fork-only TaskProgressSegments (TaskProgressStatus.tsx), so the cap (MAX_TASK_PROGRESS_SEGMENTS) lives there instead, with a test pinning both edges. That component is shared with the timeline turn-plan row, so the cap applies there too — at 24 steps the unfitted strip is ~286px of unshrinkable bar crowding out the row label, and the completed/total count still renders in both places, so no step count goes unrepresented. Review weighed gating on fit and preferred the single behaviour.

Pylon's task-dismissal helpers in ComposerTasksBadge.tsx survive; upstream's shouldShowPlanFollowUpPrompt context line was dropped from the import hunk because Pylon retired that symbol.

Verification

• vp test run across the twelve affected files — 380 tests passed.
• @t3tools/web and @t3tools/client-runtime typecheck clean; lint and format clean.
• Independent review: #8627/#8501 stat-identical to upstream; #8532 differs from upstream by exactly the two branding lines; the useLayoutEffect lands in ChatViewContent scope with complete deps; data-chat-composer-main-surface confirmed present so the shoulder reserve measurement is live.
• Not done: a browser pass. The keybindings rewrite has no rendering coverage, and the four spacing spots and the timeline segment row should be eyeballed at 1280×820 before merge.

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Claude Fable 5 in Pylon.

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[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

ℹ️ The exact PR base did not have a successful artifact. Baseline uses the latest successful main measurement shown below.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	13.3 KiB	13.3 KiB	−6 B (−0.0%)	15.1 KiB	✅
Codex	Thread snapshot wire	6.9 KiB	6.9 KiB	0 B (0.0%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.4 KiB	6.4 KiB	−6 B (−0.1%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	55.5 KiB	55.5 KiB	0 B (0.0%)	66.4 KiB	✅
Codex	Live turn messages	9	9	0 (0.0%)	21	✅
Claude	Total thread wire	13.3 KiB	13.3 KiB	+3 B (+0.0%)	15.1 KiB	✅
Claude	Thread snapshot wire	6.9 KiB	6.9 KiB	−4 B (−0.1%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.4 KiB	6.4 KiB	+7 B (+0.1%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	56.4 KiB	56.4 KiB	0 B (0.0%)	66.4 KiB	✅
Claude	Live turn messages	10	10	0 (0.0%)	21	✅

Baseline: 750d503 · PR result: f19e3d9 · 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: 109.4 KiB
• Claude decoded thread snapshot: 110.1 KiB

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