[Salochi]

Problem

A chat link to a folder outside the workspace (for example /home/me/projects/favicon-preview/) opens the file surface with "The path is a directory or special file, not a regular file." Folders inside the workspace open in the tree, but a host path cannot be revealed there, so the surface gives up. The user then has to find each file and link it by hand.

Change

When the file surface's read of a host path fails with path_not_file, it now shows a flat, read-only listing of that folder instead of the error:

• Folders first, then files, in natural sort order (reuses fileBreadcrumbChildren).
• Clicking a file opens it in the normal preview. Clicking a subfolder, or the Up to … row, lists that folder in place, through the same onOpenFile path as chat links.
• New HostFolderListing.tsx. filePath.ts gains hostFolderChildPath and hostFolderParent (POSIX and Windows separators, drive roots).

No server or contract change. The listing uses the existing projects.listEntries with the folder as cwd and directoryPath: "" (immediate children only, no index), which filesystem:read already authorizes. Sessions without that permission see the same "cannot read host files" state as before.

Workspace folders and every existing file preview are unchanged.

Scope and approval

Fork UX improvement to an existing surface (Nick asked for it after hitting the error on host folder links). It stays read-only and reuses an existing RPC and permission.

Verification

• vp test run apps/web/src/components/files/filePath.test.ts apps/web/src/components/files/FilePreviewPanel.test.ts passes, with new cases for joining and parent paths: trailing slashes, /, /home → /, C:\Users → C:\.
• tsc --noEmit -p apps/web passes.
• Manual, on a live T3 Hermes server: clicked a chat link to /home/aeris/projects/favicon-preview/; got the listing and opened PNG and GIF previews from it. Image previews from host folders depend on the companion fix in "fix(web): images outside the workspace preview from the file surface". Up to /home/aeris/projects navigated up.
• Not checked: mobile (separate files screen, unchanged), and very large folders. The listing renders every entry, the same as the breadcrumb menu.

Screenshots: none captured. Chromium doesn't run on the box this was built on. Before was the error text quoted above; after is the plain list. Happy to add captures if wanted.

Model/harness: Claude Opus 5.5 via Hermes Agent (ACP) in T3 Code.

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[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	5.0 KiB	5.0 KiB	0 B (0.0%)	6.8 KiB	✅
Codex	Thread snapshot wire	3.8 KiB	3.8 KiB	0 B (0.0%)	4.9 KiB	✅
Codex	Live turn WebSocket wire	1.2 KiB	1.2 KiB	0 B (0.0%)	2.0 KiB	✅
Codex	Live turn WebSocket decoded	20.9 KiB	20.9 KiB	0 B (0.0%)	29.3 KiB	✅
Codex	Live turn messages	2	2	0 (0.0%)	8	✅
Claude	Total thread wire	5.0 KiB	5.0 KiB	0 B (0.0%)	6.8 KiB	✅
Claude	Thread snapshot wire	3.8 KiB	3.8 KiB	0 B (0.0%)	4.9 KiB	✅
Claude	Live turn WebSocket wire	1.2 KiB	1.2 KiB	0 B (0.0%)	2.0 KiB	✅
Claude	Live turn WebSocket decoded	21.2 KiB	21.2 KiB	0 B (0.0%)	29.3 KiB	✅
Claude	Live turn messages	2	2	0 (0.0%)	8	✅

Baseline: cb44cd7 · PR result: 21cb889 · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 108.5 KiB
• Claude decoded thread snapshot: 108.8 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.

[Salochi]

Superseded by upstream pingdotgg/t3code#15045 (synced here as aa35fb3, "folder breadcrumbs navigate to parent folders"). Host folders outside the workspace now open as a file tree rooted at that folder, which covers this flat listing and more. Closing instead of resolving the conflict. Branch kept for reference.

Image previews inside those host folders still need #224: upstream's WorkspaceImagePreview still requests a workspace-file asset.