fix(md): file streaming patch preview

[icecrasher321]

Summary

Fixes markdown file preview flicker during streamed workspace file edits by guarding preview activation, replay, reconnect, and cache handoff state.

Type of Change

• Bug fix

Testing

Tested manually

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
docs	Skipped		May 6, 2026 3:38am

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PR Summary

Medium Risk
Touches core chat streaming/preview session state and resource activation behavior, which can cause regressions like incorrect tab switching or stale preview content if edge cases were missed. Changes are localized to preview-session handling and add tests to reduce risk.

Overview
Reduces file-preview flicker during streamed file edits by only rendering/activating streaming previews once a session has renderable content (via new hasRenderableFilePreviewContent).

Hardens preview session reconciliation by preventing replayed/stale streaming events from overwriting completed sessions (shouldReplaceSession), tracking which tab “owned” a preview to decide when auto-activation is allowed, and suppressing resource auto-selection during handoff from preview completion to persisted file resources.

On preview completion, seeds the workspace file-content query cache with the final preview text and tightens completion success checks before adding/activating the resulting file resource. Updates unit tests to cover renderability and session replacement rules.

^{Reviewed by Cursor Bugbot for commit 6f4bbe6. Configure here.}

[greptile-apps]

Greptile Summary

This PR guards markdown file preview activation, replay, reconnect, and cache handoff state to eliminate flicker during streamed workspace file edits. The core fix is adding hasRenderableFilePreviewContent as a gate so the preview panel and active-resource switching only fire once actual streamed content has arrived, rather than on the first lifecycle event.

• hasRenderableFilePreviewContent is introduced as a shared predicate (previewText.length > 0 || previewVersion > 0) and threaded through ResourceContent, mothership-view, and use-chat to gate all activation, chrome-sync, and UI render paths.
• shouldReplaceSession gains a guard that prevents replayed streaming events from overwriting a fully-completed session, fixing reconnect state regression.
• Resource event handoff (completedPreviewResourceHandoffRef) coordinates between the file_preview_complete handler and the subsequent resource event so that activation is suppressed when the preview panel was already managing focus.

Confidence Score: 5/5

Safe to merge; the change is a targeted guard around preview activation that does not alter the underlying streaming or file-write logic.

All activation, cache-seed, and resource-handoff paths gate correctly on hasRenderableFilePreviewContent. The reconnect-replay guard in shouldReplaceSession is tested and closes a real regression. No data-loss or activation race was introduced in the changed paths.

The resource event handler in use-chat.ts grew significantly; reviewers should follow the completedPreviewResourceHandoffRef cleanup flow (both the stale-handoff branch at ~3011 and the current-handoff branch at ~3034) to verify nothing is leaked if a resource event arrives without a corresponding preview session.

Important Files Changed

Filename	Overview
apps/sim/app/workspace/[workspaceId]/home/hooks/use-file-preview-sessions.ts	Adds hasRenderableFilePreviewContent predicate and a replay guard in shouldReplaceSession; both are well-tested and correct.
apps/sim/app/workspace/[workspaceId]/home/hooks/use-chat.ts	Large changeset introducing activation-owner tracking, handoff refs, cache seeding, and suppression logic; logic is sound but inline latestPreviewForResource and complex handoff cleanup increase maintenance surface.
apps/sim/app/workspace/[workspaceId]/home/components/mothership-view/components/resource-content/resource-content.tsx	Correctly removes the stale previewSession && guard from the streaming-file branch and adds hasRenderableFilePreviewContent checks to both derived text values.
apps/sim/app/workspace/[workspaceId]/home/components/mothership-view/mothership-view.tsx	Tightens shouldShowStreamingFilePanel to gate on hasRenderableFilePreviewContent; minimal and correct change.
apps/sim/app/workspace/[workspaceId]/home/hooks/use-file-preview-sessions.test.tsx	New tests cover the pending-empty, version-gated renderable, and completed-session replay cases for the two new exported functions.

Sequence Diagram

sequenceDiagram
    participant Stream as SSE Stream
    participant Chat as use-chat handler
    participant Sessions as useFilePreviewSessions
    participant Resources as Resources state
    participant UI as ResourceContent

    Stream->>Chat: file_preview_start
    Chat->>Sessions: upsert(pending, v=0, text='')
    Note over UI: guard: hasRenderable=false - no activation

    Stream->>Chat: file_preview_target
    Chat->>Chat: rememberPreviewActivationOwner(session)
    Chat->>Sessions: upsert(baseSession)
    Chat->>Resources: syncPreviewResourceChrome (activate if autoActivate)

    Stream->>Chat: file_preview_content (first)
    Note over Chat: prevSession has no renderable content
    Chat->>Sessions: upsert(streaming, v=1, text='...')
    Chat->>Resources: syncPreviewResourceChrome - activate preview
    UI-->>UI: streamingPreviewText defined - render FileViewer

    Stream->>Chat: file_preview_content (subsequent)
    Note over Chat: prevSession already renderable - skip chrome sync
    Chat->>Sessions: upsert(streaming, v=N, text='...')

    Stream->>Chat: file_preview_complete (success=true, id matches)
    Chat->>Sessions: complete(session)
    Chat->>Resources: setResources (add real file, remove streaming-file)
    Chat->>Chat: completedPreviewResourceHandoffRef.set(fileId)
    Chat->>Chat: seedCompletedPreviewContentCache(fileId, previewText)

    Stream->>Chat: resource event (file added)
    Chat->>Chat: read completedPreviewHandoff - suppressActivation?
    alt suppress activation
        Chat->>Resources: setResources (add without activating)
    else normal
        Chat->>Resources: addResource - activate
    end
    Chat->>Chat: delete handoff ref (cleanup)

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[icecrasher321]

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[icecrasher321]

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^{Reviewed by Cursor Bugbot for commit 6f4bbe6. Configure here.}