[Bug]: CodeView crashes with duplicate id when a regular file becomes a symlink

[branislavbudzak]

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

Steps to reproduce

1. Create a Git repository where AGENTS.md is a regular tracked file and CLAUDE.md is another regular tracked file:

   git init t3-codeview-type-change
   cd t3-codeview-type-change
   git config user.name "T3 repro"
   git config user.email "t3-repro@example.invalid"
   printf 'canonical instructions\n' > CLAUDE.md
   printf 'duplicated instructions\n' > AGENTS.md
   git add AGENTS.md CLAUDE.md
   git commit -m baseline

2. Open the repository in T3 Code and start a thread.

3. During a turn, replace the regular file with a relative symlink and commit it:

   rm AGENTS.md
   ln -s CLAUDE.md AGENTS.md
   git add AGENTS.md
   git commit -m 'use shared instructions'

4. After the turn checkpoint is created, open the turn diff or Changes view.

The checkpoint transition is a valid Git type change:

mode change 100644 => 120000 AGENTS.md

With git diff --no-renames, Git represents it as two file blocks with the same path:

diff --git a/AGENTS.md b/AGENTS.md
deleted file mode 100644
--- a/AGENTS.md
+++ /dev/null

diff --git a/AGENTS.md b/AGENTS.md
new file mode 120000
--- /dev/null
+++ b/AGENTS.md

This was also reproduced outside the original project with a minimal temporary repository.

Expected behavior

CodeView should render the regular-file-to-symlink transition as one type-change item, or safely two patch blocks with distinct internal IDs. A valid Git diff should not crash the thread view.

Actual behavior

The CodeView renderer throws a duplicate-ID error and T3 Code displays a full-page "Something went wrong" state:

Error: CodeView.addItem: duplicate id "AGENTS.mdAGENTS.md"
    at appendItemsInternal (t3code://app/assets/diffFileContents-*.js)
    at setItems (t3code://app/assets/diffFileContents-*.js)

The repository and symlink remain valid. In a second occurrence on 2026-09-10, Try again, Reload app, and fully restarting the application did not recover the affected thread: its persisted open diff panel was restored and triggered the crash again. The original conversation was recovered by closing only its persisted right panel, as described below.

The path-only identity collision has since been confirmed by a maintainer in this comment. The actual key contains a NUL separator: AGENTS.md\0AGENTS.md, which is invisible in the displayed error.

Related but distinct:

• [Bug]: Diff view captures only the first few edits from a turn and shifts the rest to the next turn #1434 concerns edits being assigned to the wrong turn. This report is a deterministic renderer crash on a valid type-change patch.
• Add Project browser and path autocomplete omit symlinked directories #8408 concerns browsing symlinked directories, not rendering a file type change.

Impact

Major degradation or frequent failure

The affected turn cannot be reviewed in CodeView. If its diff panel was open, the entire existing thread can remain inaccessible across application restarts. Creating a new thread is not necessary to recover the original conversation.

Version or commit

T3 Code desktop 0.0.40

Environment

• macOS 26.6.1, Apple Silicon arm64
• T3 Code desktop 0.0.40
• Codex CLI 0.154.0
• Node.js 26.8.1

Logs or stack traces

T3 Code (Alpha) 0.0.40
Error: CodeView.addItem: duplicate id "AGENTS.mdAGENTS.md"
    at appendItemsInternal (t3code://app/assets/diffFileContents-*.js)
    at setItems (t3code://app/assets/diffFileContents-*.js)

Verified recovery of the original thread (desktop 0.0.40)

A second occurrence happened after a turn completed using Claude Opus 5, so the observed failure is not limited to the Codex provider. This is an additional observation, not proof of provider causality.

Inspection of the installed 0.0.40 source maps and the live application showed:

• rightPanelStore.ts persists panel state in localStorage under t3code:right-panel-state:v2 (persisted schema version 11).
• The affected entry in state.byThreadKey had isOpen: true, surfaces: [{ id: "diff", kind: "diff" }], and activeSurfaceId: "diff".
• Changing only that entry's isOpen to false, then reloading, restored the same thread. The conversation, latest completed response, and message composer were visibly accessible again.
• No conversation database, checkpoint, repository file, or symlink was modified for this recovery.

For another user stuck on the error page in 0.0.40, open View > Toggle Developer Tools > Console. This version-specific workaround identifies the current thread from its URL, saves a sessionStorage backup, closes only that thread's panel, and reloads:

(() => {
  const storageKey = "t3code:right-panel-state:v2";
  const raw = localStorage.getItem(storageKey);
  const data = JSON.parse(raw ?? "null");
  const threadId = location.hash.split("?")[0].split("/").filter(Boolean).at(-1);
  const panels = data?.state?.byThreadKey;
  const matches = Object.keys(panels ?? {}).filter(
    key => key.endsWith(":" + threadId)
  );
  if (!threadId || matches.length !== 1) {
    throw new Error("Expected exactly one current-thread panel; nothing changed.");
  }
  sessionStorage.setItem("t3-recovery-right-panel-backup", raw);
  panels[matches[0]].isOpen = false;
  localStorage.setItem(storageKey, JSON.stringify(data));
  location.reload();
})();

The recovery operation was verified on the affected thread using its explicit scoped key. The snippet above generalizes key selection to the current route. Avoid reopening the affected diff until the renderer fix is available. Clearing all localStorage or deleting the thread is unnecessary.

Additional fix and regression suggestions

The maintainer's proposed unique identity fix addresses the collision. These additional cases would cover the persistent lockout and prevent partial fixes:

1. Preserve both patch halves. Do not deduplicate by path and silently discard the deletion or symlink addition. If rendering two items, assign deterministic distinct IDs and use them consistently for collapse, selection/reveal, and annotation behavior. If merging, retain the old/new modes and contents.
2. Contain rendering failures within the diff panel. Keep the conversation and composer mounted, with a local error fallback offering to close the panel. The close action should persist isOpen: false, so restarting cannot restore the same failing panel indefinitely.
3. Regression coverage: regular file to symlink and the reverse; both patch halves and contents preserved; unique stable item IDs; collapse/reveal behavior after rerender; and reopening a thread with a persisted open diff panel. A deliberately failing diff renderer should leave the conversation usable and allow persistent panel closure.

The persisted-panel recovery is directly verified. The implementation and regression items above are suggestions, not a tested code patch.

[juliusmarminge]

Thanks for the tight repro — this looks like a real renderer crash, not a bad repository.

What’s going on

Git’s regular-file → symlink transition at the same path is a valid type change (100644 → 120000). With the usual patch form that is two diff --git blocks for the same path (delete the regular file, add the symlink). Checkpoint diffs from git diff --patch are fine; the failure is on the web side when those two blocks are turned into CodeView items.

parsePatchFiles from @pierre/diffs keeps both files. For non-renames it then drops prevName, so both halves resolve to AGENTS.md. buildFileDiffIdentityKey() in apps/web/src/lib/diffRendering.ts is only previous path + current path, so both items get AGENTS.md\0AGENTS.md. DiffPanel / AnnotatableCodeView pass that through as the CodeView id. Pierre’s CodeView.addItem throws on the duplicate; there is no local error boundary, so the root route shows “Something went wrong.”

The printed id "AGENTS.mdAGENTS.md" matches that key with the NUL separator hidden. Your path-only-id inference is right.

The same collision would hit working-tree / branch diffs in the same panel. PR CodeView keys by Pierre cacheKey, and mobile review ids include file.type, so those surfaces are less likely to throw.

Not a duplicate of

• [Bug]: clicked the "diff" button to open diff in right panel and UI crashed with "duplicate id" error #9427 / fix(server): keep a/ and b/ prefixes in rendered git patches #9438 — same CodeView.addItem: duplicate id crash class, but that one was empty names from diff.noprefix. Prefixes are already pinned.
• [Bug]: Diff view captures only the first few edits from a turn and shifts the rest to the next turn #1434 — edits assigned to the wrong turn.
• Add Project browser and path autocomplete omit symlinked directories #8408 — browsing symlinked directories.

Next step

Keep unique CodeView ids for same-path type-change halves (include type and/or mode in the identity key, or suffix collisions). Add a regression around the delete + new file mode 120000 patch. Optionally contain CodeView errors so one bad patch cannot take down the whole thread view.

Workaround still holds: avoid that turn’s diff, or start a new thread after the symlink is already in the tree.