perf(web): defer image URL requests for thread history

[t3dotgg]

Opening a thread requested signed URLs for every loaded image, including images in rows that were not mounted.

Mounted user rows now request their own image URLs, including gallery images and annotation crops. Local previews and offscreen upload handoffs keep the existing preload and cleanup flow.

Asset TTLs, virtualization, and mobile code are unchanged. Assistant markdown and worklog images keep their existing queries.

Checks

• All 242 focused tests and web typecheck passed.
• Targeted lint has no new warnings. Formatting passed.
• A Node proof using the real asset atoms reduced initial requests from 300 or 3,000 to 15. Each fixture mounted four user rows and kept one offscreen handoff active.
• The proof checked gallery URLs after row unmount, crops, handoffs, environment isolation, URL refresh, and independent markdown and worklog requests.

Newly mounted history rows can wait for their first signed URL. No browser or device run was used.

Created with GPT-6 Astra (preview) in Codex.

---

Note

Medium Risk
Changes when and how chat image URLs are fetched; history rows may briefly lack signed previews until mount, but scope is limited to web chat attachments with dedicated tests.

Overview
Stops prefetching signed URLs for every image in loaded thread history and instead loads them only where they are needed.

ChatView now builds asset requests with selectHandoffImageResources, so offscreen upload handoffs still get server URLs while the rest of history is not scanned for signing. Each mounted user timeline row in MessagesTimeline calls selectMessageImageResources and useAssetUrls for its own gallery (including crops), skipping attachments that already use blob: or data: previews. Preview wiring uses createMessageAttachmentPreviewProjector so signed URLs apply only after local handoff previews are released.

New session-logic tests cover resource selection, empty-handoff fast paths, and handoff vs row preview behavior.

^{Reviewed by Cursor Bugbot for commit ba96662. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Defer image URL requests for thread history in ChatView

• Adds selectHandoffImageResources and selectMessageImageResources selectors in session-logic.ts that deduplicate image attachment IDs and skip attachments with local blob: or data: preview URLs.
• ChatView.tsx now requests stored image URLs only for user messages with pending preview handoffs, instead of for every image attachment in loaded server history.
• MessagesTimeline.tsx requests image URLs per mounted user-message row and projects resolved URLs into displayed image attachments; file, video, and unknown attachments still use original message data.
• Behavioral Change: ChatView no longer bulk-requests image URLs for all server-history attachments; consumers expecting eager URL resolution for full history must rely on per-row mounting instead.

^{Macroscope summarized ba96662.}

[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	13.8 KiB	+248 B (+1.8%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.0 KiB	7.0 KiB	−3 B (−0.0%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.5 KiB	6.7 KiB	+251 B (+3.8%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	57.0 KiB	58.5 KiB	+1.5 KiB (+2.6%)	66.4 KiB	✅
Codex	Live turn messages	8	10	+2 (+25.0%)	21	✅
Claude	Total thread wire	13.6 KiB	13.5 KiB	−79 B (−0.6%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.0 KiB	7.0 KiB	−3 B (−0.0%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.6 KiB	6.5 KiB	−76 B (−1.1%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	57.9 KiB	57.8 KiB	−88 B (−0.1%)	66.4 KiB	✅
Claude	Live turn messages	10	8	−2 (−20.0%)	21	✅

Baseline: d7cf8aa · PR result: ba96662 · 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: Approved at ba96662

Macroscope's review found this PR approvable — This is a narrowly scoped web performance change that defers signed image URL requests for offscreen thread history while preserving mounted-image loading and pending-preview handoffs. It adds no schema, deployment, security-sensitive behavior, or new user-facing capability, and the core selection and preview-projection behavior is covered by tests.

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