fix(web): binary files get a real empty state instead of a raw read error

[tsouth89]

Closes part of #4973.

What changed

Clicking a chat file link for a build artifact — an installer, an archive, a recording — opened the file panel onto a dead end. The panel printed the read error verbatim in red: it named the internal failure, repeated the absolute workspace root, and offered nothing to do next.

The panel had no way to tell a binary file apart from any other read failure. The server raises a typed WorkspaceBinaryFileError, but ws.ts folds it into ProjectReadFileError, so the only thing that survives to the client is the structured failure discriminator — and the query state was dropping it on the floor. This surfaces that field, then renders a proper empty state for binary_file that names the file and hands back its path. Every other read failure keeps the message it shows today.

Why

#4973 asks for artifacts T3 Code cannot open to stop being useless links. #5366 covers the context-menu half of that with "Open in folder". This is the other half: the state you actually land on when you click. The two compose — once #5366 lands, "Open in folder" is the natural second action to drop into this empty state.

Keying on failure rather than the error message also means the panel is no longer one prose edit away from silently falling back to the raw string.

UI changes

Before	After

Captured in a real client against a 9.6 MB .exe in the workspace, dark theme, file explorer collapsed so the preview area is legible.

Verification

• vp test run src/components/files/FilePreviewPanel.test.ts --project unit — 9 passed
• pnpm --filter @t3tools/web typecheck
• vp lint on the four changed files
• One integrated pass in a real client: opened a binary artifact in the file panel and confirmed the empty state renders and Copy path copies the absolute path. The before/after images above are from that pass.

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for the UI change
• I included a video for animation/interaction changes — not applicable, no motion

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Written by Claude Opus 5 in Claude Code.

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Note

Low Risk
UI-only branching on an existing server failure code; non-binary errors unchanged and behavior is covered by new unit tests.

Overview
When a workspace file read fails because the content is not UTF-8 text (binary_file), the file preview panel now shows a dedicated empty state instead of the raw server error string.

Project file query hooks expose a structured errorFailure alongside the error message so the UI can branch on failure type without parsing prose. FilePreviewPanel uses that to render BinaryFilePreview: a short description naming the file (basename only) and an optional Copy path action when an absolute path is available. Other read failures still use the existing destructive error message.

Helpers isBinaryFilePreviewError and binaryFilePreviewDescription in filePreviewMode.ts centralize detection and copy; unit tests cover them.

^{Reviewed by Cursor Bugbot for commit e167768. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Replace raw read error with empty state UI for binary file previews

• Adds isBinaryFilePreviewError and binaryFilePreviewDescription helpers in filePreviewMode.ts to detect and describe binary file failures using a structured 'binary_file' failure code.
• Introduces a BinaryFilePreview component in FilePreviewPanel.tsx that shows an empty state with the filename and a 'Copy path' button (with clipboard feedback) instead of a raw error message.
• Extends query state in projectFilesQueryState.ts to surface a structured errorFailure field alongside error, enabling the panel to branch on failure type.

^{Macroscope summarized e167768.}

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Approvability

Verdict: Approved 2597729

This is a straightforward UI improvement that replaces a raw error message with a friendly empty state for binary files. The changes are self-contained, use existing UI primitives, and include unit tests with no runtime behavior changes beyond better error presentation.

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