fix(web): size the chat image slot from server-reported dimensions

[juliusmarminge]

Stack 3/3 (#10201). Depends on #10198.

Problem

After #9938 a workspace image on web still moved the rows below it once: a portrait screenshot grew past its 16:9 slot when it decoded.

Fix

ChatMarkdownAssetImage applies the server's imageDimensions (#10198) through the existing authoredImageSizeStyle, so the slot is the image's final box from the moment the URL resolves. An authored width/height still wins; a caller's cap (the viewed-image row's maxHeight: 16rem) layers on top rather than shadowing the dimensions.

Evidence

Cold thread mount with image responses delayed 4 s, layout-shift observer armed before mount (same harness as #9938):

	#9938	this PR
Media layout-shift entries	1 (0.013 — portrait growing past 16:9)	0

The only remaining entry on the page is the composer resizing, unrelated to media.

Verification

• ChatMarkdown.workspace-images.test.tsx: slot is sized from server dimensions (width: 720px; aspect-ratio: 720 / 1400); authored size overrides server dimensions. 32 passed.
• apps/web typecheck clean.
• In-browser: portrait image renders with aspect-ratio: 720 / 1400 on the slot and the settled <img>; a 16rem maxHeight cap yields a 247×256 box.

Model: Claude Fable 5 · Harness: Claude Code in T3 Code

🤖 Generated with Claude Code

Note

Size chat asset images from server-reported dimensions

• ChatMarkdownAssetImage now reads reported width and height from successful asset URL loads and derives inline width, aspect ratio, and a height-derived max-width
• authoredImageSizeStyle gains an optional height-cap argument (default 30rem); when both dimensions are present the cap is folded into the max-width calculation
• PlainWorkEntryRow in MessagesTimeline.tsx switches from an inline max-height style to the new maxHeightRem prop, keeping the 16rem value
• Explicit incoming style props still take precedence; callers without dimensions can still apply a custom rem height cap as a fallback
• Risk: asset images without server-reported dimensions no longer get a computed aspect ratio — they fall back to the height-cap path only, which may shift layout for previously auto-sized images in ChatMarkdown.tsx

^{Macroscope summarized d18793c.}

[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

ℹ️ No successful main baseline artifact is available yet. This run establishes the initial measurement.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	—	13.6 KiB	—	15.1 KiB	✅
Codex	Thread snapshot wire	—	7.0 KiB	—	7.3 KiB	✅
Codex	Live turn WebSocket wire	—	6.6 KiB	—	7.8 KiB	✅
Codex	Live turn WebSocket decoded	—	57.1 KiB	—	66.4 KiB	✅
Codex	Live turn messages	—	10	—	21	✅
Claude	Total thread wire	—	13.5 KiB	—	15.1 KiB	✅
Claude	Thread snapshot wire	—	7.0 KiB	—	7.3 KiB	✅
Claude	Live turn WebSocket wire	—	6.5 KiB	—	7.8 KiB	✅
Claude	Live turn WebSocket decoded	—	57.8 KiB	—	66.4 KiB	✅
Claude	Live turn messages	—	8	—	21	✅

Baseline: unavailable · PR result: d18793c · 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: 113.8 KiB
• Claude decoded thread snapshot: 114.5 KiB

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

[macroscopeapp]

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — This is a localized image-layout fix that uses existing server dimensions, preserves authored sizes, and retains explicit height caps. It also changes the default rendering of un-authored workspace images from the prior 16:9-style slot to their reported aspect ratio, making it a product-default behavior change.

No code changes detected at d18793c. Prior analysis still applies.

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