fix(web): isolate same-origin agent view lifecycles

[tusharbhardwaj-bk]

What Changed

• Coordinate URL-backed agent views by normalized origin so only one inline or expanded iframe is live at a time.
• Switch ownership through an empty commit, then mount a fresh iframe from the exact stored URL.
• Add Chromium credentialless isolation to cross-origin URL frames while preserving the opaque self-origin sandbox.
• Make Node, Vite, hosted web, and desktop HTML shells unframeable to close redirect-based sandbox escapes.
• Document browser support and authenticated-app limitations.

Why

Two immutable agent-view renders can point at different fragment-addressed rooms on one origin. Keeping both iframes mounted lets the apps share origin storage and collaboration channels, so a later card can display stale state from the earlier room even though its render ID and stored URL are correct.

The lifecycle is now serialized by origin and tested at the DOM-node boundary. credentialless adds an ephemeral Chromium partition for the top-level T3 document; it is intentionally documented as defense in depth, not per-render storage isolation. Firefox and Safari retain the exclusive remount lifecycle.

UI Changes

Historical same-origin URL cards remain visible but inactive cards show Open this view. Selecting one disconnects the current iframe before mounting a new node. The focused DOM suite records detach-before-attach and exact src values for A → B → A and expanded/pending switches.

Deployed screenshots and an interaction recording will be attached from the experimental environment during the required post-merge verification; no room fragments or keys will be captured.

Verification

• apps/web: 16 focused agent-view unit/DOM tests passed.
• apps/server: 147 focused Agent UI and static-router tests passed.
• Hosted/desktop framing tests: 9 passed.
• Web, server, and desktop package typechecks passed.
• Fork marker check passed.

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes

Written by GPT-5.6-Sol in T3 Code (Codex harness).

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[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	—	13.5 KiB	—	15.1 KiB	✅
Codex	Thread snapshot wire	—	7.2 KiB	—	7.3 KiB	✅
Codex	Live turn WebSocket wire	—	6.4 KiB	—	7.8 KiB	✅
Codex	Live turn WebSocket decoded	—	55.6 KiB	—	66.4 KiB	✅
Codex	Live turn messages	—	10	—	21	✅
Claude	Total thread wire	—	13.5 KiB	—	15.1 KiB	✅
Claude	Thread snapshot wire	—	7.2 KiB	—	7.3 KiB	✅
Claude	Live turn WebSocket wire	—	6.4 KiB	—	7.8 KiB	✅
Claude	Live turn WebSocket decoded	—	56.5 KiB	—	66.4 KiB	✅
Claude	Live turn messages	—	10	—	21	✅

Baseline: unavailable · PR result: 9472e8d · 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: 110.4 KiB
• Claude decoded thread snapshot: 111.1 KiB

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