fix(server): import agent sessions from a project's linked worktrees

[n4mr3g]

Problem

Importing a project from onboarding brings in only the sessions whose cwd is the project root. Since #10493, onboarding no longer offers linked worktrees, because their history belongs to the main checkout, but the main checkout's import never picks that history up. Any session that ran in a linked worktree is never imported anywhere.

This hits anyone who runs agents in worktrees: Claude Code desktop (every session runs in <repo>/.claude/worktrees/<name>), claude --worktree, subagents with worktree isolation, and plain git worktree add checkouts. On my machine, 52 of the last 30 days' sessions across four repos were dropped this way.

To reproduce:

1. In a normal clone, git worktree add ../repo-feature and run a Claude Code session in ../repo-feature.
2. Start T3 Code with a fresh home and import the repo from the welcome screen.
3. Only sessions that ran in the repo root are imported.

Change

prepareRecentThreads now accepts a session whose cwd is a linked worktree whose commondir resolves to the project's .git directory. The match uses the existing directoryIdentity, so aliases and case variants behave as they do for the root. T3-managed worktrees stay excluded, since their threads already exist.

An importable outcome now carries the worktree's path and the branch from its HEAD. The importer sets them as the thread's worktreePath and branch, so resuming runs the provider in the checkout the session started in.

The cost is one .git stat per candidate and two small file reads per linked worktree. No git process.

Scope and approval

Submitted as a small fix for an obvious bug: the scanner's doc comment says linked worktrees are skipped because their history belongs to the main checkout, and this makes the import do that. The welcome screen still does not list worktrees as candidates, so the onboarding UI and its behavior are unchanged.

Overlap with #16688: for bare repositories, a worktree session could match both the bare root's project and the worktree's own project. The second import hits the existing project conflict check and is skipped with a warning, so nothing is duplicated.

Verification

• vp test run apps/server/src/project/AgentSessionScanner.test.ts apps/server/src/project/AgentSessionImporter.test.ts: 83 passed, 1 failed. The failure, "excludes sandboxes reached through a symlink into the worktrees dir", also fails on main on macOS and is unrelated.
• New scanner test: a root session, a session in a linked worktree, one in a linked worktree of a different repo, and one in a T3-managed worktree of the same repo. Only the first two are imported, and the worktree session carries its path and branch. A second test covers a project whose .git is a gitdir: pointer (submodule or --separate-git-dir).
• The importer test checks that worktreePath and branch reach the created thread.
• vp run --filter t3 typecheck and vp lint apps/server/src/project: clean.
• Ran the patched scanner read-only against my real ~/.claude history for four repos: 52 importable worktree sessions (4, 9, 19 and 20), each with the worktree's current branch.

Not checked: resuming an imported worktree thread end to end in a running app, and Windows path handling for commondir.

Created with Claude Opus 5.5 in Claude Code.

🤖 Generated with Claude Code

[macroscopeapp]

Approvability

Verdict: Approved at 43174b5

Macroscope's review found this PR approvable — This is a focused server bug fix that restores import of sessions from a project’s linked worktrees and records their existing branch/path metadata for resume behavior. The production changes are localized, avoid schema or default changes, preserve exclusions, and include targeted scanner and importer tests.

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[coderabbitai]

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📥 Commits

Reviewing files that changed from the base of the PR and between 243dd64 and 43174b5.

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📒 Files selected for processing (2)

• apps/server/src/project/AgentSessionScanner.test.ts
• apps/server/src/project/AgentSessionScanner.ts

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🚧 Files skipped from review as they are similar to previous changes (1)

• apps/server/src/project/AgentSessionScanner.ts

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📝 Walkthrough

📝 Walkthrough

📝 Walkthrough

Walkthrough

Recent-thread discovery now includes linked worktrees that belong to the selected project. Imported threads retain the matched worktree path and branch when available.

Changes

Linked Worktree Thread Import

Layer / File(s)	Summary
Match linked worktrees apps/server/src/project/AgentSessionScanner.ts, apps/server/src/project/AgentSessionScanner.test.ts	The scanner matches linked worktrees by Git directory identity, accepts matching transcript paths, and reports their path and branch. Tests cover project, managed, and unrelated worktrees, plus a project whose .git file points to a separate Git directory.
Carry metadata into imported threads apps/server/src/project/AgentSessionImporter.ts, apps/server/src/project/AgentSessionImporter.test.ts	The importer copies the worktree path and branch to the created thread. Missing worktree metadata remains null; the test checks the created-thread event payload.

Priority: ⬇️ Low

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

Change: Bug fix

Sequence Diagram(s)

sequenceDiagram
  participant AgentSessionScanner
  participant AgentSessionImporter
  participant ThreadCreatedEvent
  AgentSessionScanner->>AgentSessionImporter: return importable thread with worktree metadata
  AgentSessionImporter->>ThreadCreatedEvent: emit thread with worktree path and branch

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Suggested reviewers: juliusmarminge

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Merge Risk: ⚪ Minimal · up to 43174

Linked-worktree sessions can be imported and resumed from their worktree. No merge-blocking issue is established.

Pre-merge checks | 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.
Title check		The title clearly and concisely describes the main change: importing agent sessions from linked worktrees.
Description check		The description includes complete Problem, Change, Scope and approval, and Verification sections. It explains the bug, implementation, scope, test results, known failure, and unchecked areas.

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✨ Finishing Touches

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[coderabbitai]

Actionable comments posted: 1

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• 🪄 Fix CodeRabbit comments on this PR

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Inline comments:
Review comments at @apps/server/src/project/AgentSessionScanner.ts:
- Around line 1387-1395: Update the root `.git` handling in the project setup to
resolve file-based gitdir pointers using the existing `readGitIdentity`
resolution path, then compute `gitDirIdentity` from the resolved directory.
Preserve the current behavior for directory-based `.git` entries.

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📥 Commits

Reviewing files that changed from the base of the PR and between 18656a3 and 243dd64.

📒 Files selected for processing (4)

• apps/server/src/project/AgentSessionImporter.test.ts
• apps/server/src/project/AgentSessionImporter.ts
• apps/server/src/project/AgentSessionScanner.test.ts
• apps/server/src/project/AgentSessionScanner.ts

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