feat(web): customize chat timeline backgrounds

[maria-rcks]

adds wallpaper image URLs, local files, clipboard paste, opacity, blur, preview, and removal in appearance through a compact Wallpaper row below Motion with a customize menu. the menu reuses the chat's message, working timer, and tool-call renderers, and unmounts on close to stop animations and cancel unfinished imports. agent text and tool labels receive theme-colored shadows over wallpaper. blur preserves the image size and crop, avoiding horizontal drift and zoom. wallpaper stays in the chat column; user and agent messages scroll beneath the short progressive header blur, with new messages anchored below its 24px tail.

verified with web typecheck, scoped lint, passing CI, and browser checks of slider persistence, image paste, removal/reapply, close cancellation, and desktop/narrow light/dark layouts. previous timeline verification covered first-message positioning and scrolling with 149 existing tests; native OS file dialogs remain unverified, and generalized pre-decode dimension limits remain a shared image-pipeline follow-up.

new-thread composer glass now samples the wallpaper while idle: its mobile view-transition name is scoped to the transition lifetime. verified at desktop and narrow widths, including runtime transition-name activation and cleanup, web typecheck, scoped lint, and all 5 existing draft transition tests.

model: gpt-6; harness: codex.

Note

Add timeline wallpaper settings to chat view with opacity and blur controls

• Adds wallpaper image (max 1.5M chars), opacity (0–100), and blur (0–30) fields to ClientSettings with validation schemas in settings.ts; decoding defaults are empty image, opacity 20, blur 0
• Adds a wallpaper editor in Appearance settings that accepts HTTP(S) URLs or local image files, compresses local files, probes loads with a timeout, and persists results to client settings; includes thumbnail preview, opacity/blur sliders, and image removal
• Renders the wallpaper behind the timeline in ChatView.tsx via ChatTimelineBackground.tsx and a layered top-bar blur via ChatTopbarBlur.tsx; MessagesTimeline now reserves measured header height for anchor metrics, overflow checks, and minimap scrolling
• Converts user message bubbles to glass surfaces using the message surface color with text-shadow removal; the surface-glass CSS utility now accepts an optional base color variable, falling back to the normal background variable
• Risk: UserMessageBubble replaces the previous message-colored background wrapper with a glass surface — the removed background-class assertion in MessagesTimeline.test.tsx is the only in-tree test update. The top fade mask is disabled while a wallpaper is active, changing scroll appearance for timelines with a wallpaper set.

^{Macroscope summarized 3ca4946.}

[macroscopeapp]

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — This PR introduces a sizable wallpaper workflow with local/remote image persistence and changes chat timeline rendering, layering, message surfaces, and scroll anchoring. It also establishes new wallpaper product defaults, so the scope and default-setting impact merit human review.

^{You can add or adjust custom eligibility rules. Learn more.}

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