fix(web): open absolute folder links in the file explorer

[shardmods]

What Changed

Absolute folder links in chat now open a file explorer rooted at the linked folder. Opening a child file or copying/dragging a mention keeps its absolute path, so it continues to refer to the correct location outside the chat's workspace. Directory suffixes are stripped before Windows path conversion when dragging mentions.

Why

Clicking a link to /Users/user/Coding/t3code-local from a chat in /Users/user/Amethyst/design opened a file preview and failed because the target was a directory. The existing directory fallback excluded absolute paths. This extends that fallback by giving the explorer the linked directory as its root.

Related: #10909 added the workspace-relative folder fallback. #12449 handles links to the current workspace root; this fix also handles directories outside that workspace.

UI Changes

Captured in an isolated web development instance using the same seeded chat. Before: the folder link produces a read error. After: it opens the folder's contents; selecting a child file opens its contents from that folder. The shared web/desktop panel changed; native desktop and mobile were not separately exercised. Captured at 1280 × 800 against the upstream base and the PR patch.

Before	After

Before/after interaction recording — the fixed flow starts at 0:10; an idle pause is cut at 0:20.

Validation

• 22 tests passed across FilePreviewPanel.test.ts, projectFilesQueryState.test.tsx, and fileTreeDragMention.test.ts.
• Web typecheck passed with existing suggestions.
• Targeted lint passed with existing React warnings; formatting and git diff --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

Implemented and reviewed with GPT-6 through the Codex harness in T3 Code.

Summary by CodeRabbit

• New Features

  • File browsing now supports directories hosted outside the current project context.
  • File links, context-menu actions, and drag-and-drop mentions can use resolved absolute paths when viewing external directories.

• Bug Fixes

  • Improved path handling keeps displayed file links aligned with their actual project location while preserving correct selection behavior.

[coderabbitai]

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ℹ️ Recent review info

⚙️ Run configuration

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Run ID: 6bfa2984-bcb4-4e31-adfb-64001155996c

📥 Commits

Reviewing files that changed from the base of the PR and between f6cc6bc and fbb7d49.

📒 Files selected for processing (4)

• apps/web/src/components/files/FileBrowserPanel.tsx
• apps/web/src/components/files/FilePreviewPanel.tsx
• apps/web/src/components/files/fileTreeDragMention.test.ts
• apps/web/src/components/files/fileTreeDragMention.ts

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📝 Walkthrough

Walkthrough

The file explorer now supports host directories outside the chat workspace. It resolves entry paths for links, file opening, and drag mentions while preserving original tree paths for deselection.

Changes

External File Paths

Layer / File(s)	Summary
Path resolution and drag mentions apps/web/src/components/files/FileBrowserPanel.tsx, apps/web/src/components/files/fileTreeDragMention.ts, apps/web/src/components/files/fileTreeDragMention.test.ts	FileBrowserPanel optionally resolves entries against cwd. Context-menu mentions, file opening, and drag mentions use resolved paths. Drag deselection keeps the original tree paths.
Host directory explorer integration apps/web/src/components/files/FilePreviewPanel.tsx	Host directories use their relative path as the explorer CWD. The explorer remounts for the environment and CWD, displays the directory basename, enables absolute paths, and clears the selected tree path.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix

Sequence Diagram(s)

sequenceDiagram
  participant FilePreviewPanel
  participant FileBrowserPanel
  participant DragMentionController
  participant Composer
  FilePreviewPanel->>FileBrowserPanel: Pass host directory CWD and absolutePaths
  FileBrowserPanel->>FileBrowserPanel: Resolve entry path against CWD
  FileBrowserPanel->>DragMentionController: Provide resolved path callback
  DragMentionController->>Composer: Create mention with resolved path
  DragMentionController->>FileBrowserPanel: Deselect original tree path

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Suggested reviewers: maria-rcks

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 3 functions across 4 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description check	✅ Passed	The description includes all required sections, explains the change and rationale, provides UI screenshots and an interaction recording, and completes the checklist. It also documents validation resul…
Title check	✅ Passed	The title clearly and concisely describes the main change: absolute folder links now open in the file explorer.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create a new PR

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