Case-insensitive filesystems: differently-cased launch paths create duplicate project entries

Additional detail after tracing where the duplicate is actually rooted (macOS desktop app):

The sidebar groups sessions by an originCwd field that the app stores per session and leaves as the raw, un-canonicalized launch-path string — even though it canonicalizes cwd and worktreePath to the on-disk casing in the same record:

.cwd          = /Users/<you>/Projects/foo/...   <- canonicalized
.originCwd     = /Users/<you>/projects/foo        <- raw launch casing; drives sidebar grouping

The lowercase path is persisted in three stores, so a partial cleanup doesn't hold:

1. ~/.claude.json -> projects keys
2. ~/Library/Application Support/Claude/claude-code-sessions/**/local_*.json -> originCwd (also cwd/worktreePath on some)
3. Electron Local Storage (leveldb)

Editing ~/.claude.json while the app is running is also futile — the live process re-writes its own project key on the next state flush.

Suggested fix: canonicalize originCwd (e.g. fs.realpathSync.native()) at capture time and dedupe grouping keys case-insensitively on case-insensitive volumes, plus a one-time migration that merges case-variant entries across all three stores.

Concrete trigger (more actionable than manual mis-launch): the duplicate is generated by the app's own "suggested task → open in a new session" (spawn-task) feature, not by the user typing a lowercase path.

Reproduced state on a real install:

• 12 spawned sessions (records carrying spawnSeed) were written with a lowercase originCwd (/Users/<you>/projects/<repo>), while their cwd/worktreePath were canonical capital — so the new session lands under a second, differently-cased project group in the sidebar.
• The spawn records show spawnSeed: { "worktreeHookBased": true }, i.e. these follow-up sessions launch through a git-worktree path. That launch path appears to capture a non-canonical project root rather than realpath-ing it.
• Effect compounds: once one session's project root is recorded lowercase, every follow-up task spawned while working there piles into the phantom group, so it looks like a persistent, self-regenerating duplicate.

I could not confirm from the stored records whether the child inherits the parent session's raw path or the spawn/worktree code independently mis-cases it (spawnSeed stores no parent pointer) — but either way the fix is the same: canonicalize the project root at session-spawn / worktree-launch time (fs.realpathSync.native()), don't propagate a raw path string. Repos that use git worktrees heavily hit this far more than typical users.

Same root cause, different trigger — worth folding into whatever normalisation fixes this: on Windows, path separators produce the same duplication as case does.

C:\Users\<u>\…\repo\project-main and C:/Users/<u>/…/repo/project-main are one directory, and both spellings are valid and equivalent on Windows, but they are stored and rendered as two separate entries. In my install:

| spelling | session records |
|---|---:|
| C:\Users\…\repo\project-main | 116 |
| C:/Users/…/repo/project-main | 4 |

Two rows in the picker, identical labels, distinguished only by a truncated path.

One addition that may matter for the fix: this is not only the ~/.claude.json projects map. The Claude Code folder picker in the desktop app duplicates the same way, and its list is built from a different store — the originCwd field of %APPDATA%\Claude\claude-code-sessions\<…>\local_*.json. I verified they are independent: pruning ~/.claude.json to 9 project entries left the picker showing a different set of 10. So path normalisation likely needs to happen in both places, or in a shared helper.

Filed the picker side with full measurements in #86181 (it also covers deleted folders never leaving the list, which is separate from this issue).