feat(chat): preview agent media on web and mobile

[gabrielelpidio]

Problem

Agent-produced images and saved browser evidence are currently shown as paths instead of useful previews. The previous implementation in #4872 depended on the V1 orchestration layer removed by #2829.

What changed

• add a durable orchestration V2 image_view turn item and project Codex imageView / saved imageGeneration events into it
• render V2 image outputs and markdown image/video paths in web and mobile chat
• resolve workspace media, browser artifacts, and V2 thread images through short-lived signed asset URLs
• persist preview_snapshot evidence either to a unique server artifact (save: true) or a validated workspace-relative PNG (savePath)
• harden external-file serving and screenshot writes against traversal and symlink swaps

Codex has a native image event and now emits the first-class V2 item. Other providers still get provider-independent markdown media rendering until their adapters expose an equivalent native event.

Important

This PR is intentionally stacked on #2829. TODO: retarget/rebase it to main after #2829 merges.

Verification

• 8 focused test files, 111 tests passed
• contracts, shared, web, and mobile typechecks passed
• real V2 Codex turn persisted a completed image_view item and rendered the same projection in web and iOS
• web and iOS both rendered the first-class V2 image output and a relative markdown workspace image; image expansion was also exercised

The server typecheck currently reaches the existing #2829 error in untouched apps/server/src/mcp/toolkits/worktree/registration.test.ts (ServerConfig | WorkspacePaths missing from the expected test context). #2829's own Check and Test jobs are already failing at this base head.

Screenshots

Web — inline previews

Web — expanded preview

Mobile — iOS

Reimplements the media-preview work from #4872 against orchestration V2.

Model: GPT-5.6-Sol
Harness: T3 Code (Codex)

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Note

High Risk
Touches signed asset serving, symlink-safe file I/O, and new asset claim types—security-sensitive paths that must stay fail-closed; broad surface across server, contracts, web, and mobile.

Overview
Adds inline image and video previews in web and mobile chat instead of raw paths, reimplemented on orchestration V2 after the V1 layer removal.

Orchestration & feed: Introduces a durable V2 image_view turn item (Codex imageView / saved imageGeneration). Completed items surface as dedicated image-output timeline/feed rows; failed ones stay in the work log.

Markdown media: New MarkdownMedia (web + mobile) resolves markdown img/video via resolveMarkdownMediaSource—direct URLs, thread workspace files, browser-artifact, or thread-image—and loads them through signed asset URLs with loading/error UI and image expand.

Assets & server: Extends AssetResource with browser-artifact and thread-image; video workspace previews use exact-file claims. resolveAsset can return streamed open-file responses. noFollowFile hardens reads/writes and screenshot persistence against traversal/symlinks.

Preview MCP: preview_snapshot can save: true (server artifact + savedScreenshotPath) or savePath (validated workspace PNG); tool hints updated accordingly.

Mobile markdown: renderImage / context lets native selectable markdown delegate image nodes to the same media pipeline.

^{Reviewed by Cursor Bugbot for commit 0387ef2. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Add inline media preview for agent images and videos in web and mobile chat

• Adds image_view as a new turn item type in the orchestration V2 contract, projected from Codex image/imageGeneration items and emitted as image-output timeline/feed entries in both web and mobile.
• Web chat renders image-output rows as clickable thumbnail previews via ImageOutputTimelineRow, and markdown img/video tags are now rendered through a new MarkdownMedia component that resolves thread-scoped asset URLs.
• Mobile chat adds MarkdownMedia and ThreadImageOutput components with loading, unavailable, and tap-to-expand states; custom image rendering is injected into markdown via a new renderImage prop and React context.
• The preview_snapshot MCP tool now accepts optional save (boolean) or savePath parameters to persist screenshots either to the server's browser-artifacts store or a workspace-relative path, with symlink traversal protection.
• New AssetResource variants (browser-artifact, thread-image) are added to contracts, with corresponding resolveAsset and issueAssetUrl logic backed by no-follow file opening on Linux, macOS, and other platforms.
• Risk: resolveAsset now returns an open-file variant with a ReadStream in addition to the existing file variant; callers that exhaustively switch on ResolvedAsset must handle the new case.

^{Macroscope summarized 0387ef2.}

[andybergon]

Fresh reproduction after #6433 merged:

• Server: T3 Code Nightly 0.0.34-nightly.20260824.1172; Android client version not captured.
• A Codex turn returned three valid PNGs through the image-view tool.
• Desktop rendered all three in the work stream.
• Mobile did not expose them as tappable or downloadable images, and the completed turn’s final message could not preserve them as normal attachments.
• Current source routes normal attachments and workspace Markdown images to the full-screen viewer, but image-view results remain trapped in tool output.

This confirms that the first-class agent image-output path covered by this PR is still needed after #6433.