Render-time filesystem probes (canonicalize / exists) run per row on the GPUI thread #154

Status — still open (reviewed 2026-08-22)

The broader #155 I/O sweep moved operations that can be offloaded away from the GPUI thread, and chat.rs has since been split into chat/mod.rs + chat/model.rs + components — but the synchronous render-path probes remain on current main (e8a5f1cc).

Current evidence

• crates/services/src/user_files.rs:5: relativize_to_workspace canonicalizes the workspace root on every call.
• Render callers: crates/ui/src/chat/model.rs:560, crates/ui/src/chat/components/changed_files.rs:105, crates/ui/src/diff/view.rs:99 and :182, and crates/ui/src/markdown/view.rs:208.
• crates/ui/src/markdown/link_target.rs:49 still calls path.exists() while resolving relative Markdown-link candidates.

Impact

The calls scale with changed-file rows and Markdown links and can repeat as views rebuild. Local filesystems make the cost easy to miss; network or slow filesystems can turn it into visible frame-time work.

Direction

Cache rather than offload:

• canonicalize the workspace root once per active cwd/session and pass the resolved root into render models;
• keep a small document-scoped link-target existence cache, invalidated on document/base-dir changes (or explicitly accept bounded staleness).

Acceptance criteria

• Rendering changed-file rows and Markdown links performs no filesystem I/O.
• Cache invalidation is covered when cwd/base directory or Markdown content changes.
• A render-focused test or instrumentation check prevents these probes from returning.

Effort: S–M · Risk: LOW