[Bug]: Agent file links to Claude Code's scratch folder are unclickable, or open a file named "..." #30757

Before submitting

• I searched existing issues and did not find a duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

apps/web (file-link detection in chat), and the agent instructions T3 adds to Claude threads

Steps to reproduce

1. Run a Claude thread in a worktree on a Linux server. T3 server 0.1.8-nightly.20261104.4165, Claude Code 2.1.318, macOS desktop client.
2. Have the agent save a file to its scratch folder and mention it. Claude Code's scratch folder has a long path with segments that start with a dash, for example:
   /tmp/claude-1000/-home-me--t3-worktrees-proj-t3-abc123/<session-uuid>/scratchpad/notes.md
3. The agent writes the path the way T3's instruction asks ("Link any other file you produce using its absolute path"). Observed in one thread, it did that in three ways:
   • A. As plain text, in full.
   • B. In inline code, shortened with an ellipsis: `/tmp/claude-1000/...`.
   • C. As a Markdown link: [notes.md](/tmp/claude-1000/-home-me--t3-worktrees-proj-t3-abc123/<session-uuid>/scratchpad/notes.md).
4. Click each one.

Expected behavior

The file opens read-only in the file viewer, as for other absolute paths outside the workspace (#9140).

Actual behavior

• A: The path is not turned into a link. There is nothing to click. I haven't isolated which part of the path stops detection. The dash-led segments are my guess.
• B: The text becomes a file chip. Clicking it asks the server for a file literally named ...:

  WorkspaceFileSystemOperationError: Workspace file operation 'realpath-target' failed at '/tmp/claude-1000/...'
  

  The viewer then shows "The file could not be accessed or read" with "Attempted path /tmp/claude-1000/...". This looks like T3 cut the path short, but it was the agent's own shorthand.
• C: Works.

Only form C works reliably, and the instruction doesn't ask for it.

Suggested fix

1. Make the agent instruction name the format that works, for example: "Link each file you produce as a Markdown link with its absolute path, [name](/abs/path). Never shorten the path."
2. Detect long absolute paths in plain text, including segments that start with -.
3. Don't make a file chip from a path whose last segment is ..., or any other run of dots only.

Item 1 alone would have prevented this, for every agent and machine.

Impact

Minor bug or occasional failure. Each time it happens, the user sees a broken or missing link to a file the agent just made, and it looks like T3 can't read /tmp.