fix: resolve_target fallback via git worktree list for external worktrees

[helizaga]

Summary

• Adds a git worktree list --porcelain fallback as the last step in resolve_target() before returning "not found"
• Catches worktrees created outside the gtr-managed directory (e.g. via raw git worktree add /some/other/path -b feature) that the existing directory scan cannot find
• Only runs when all existing fast paths fail — zero performance impact on the happy path

Note: Issue #127 was closed as already fixed by #123/#126 (discover_repo_root fix). This PR addresses a separate gap where resolve_target couldn't find worktrees stored outside the gtr-managed worktrees directory.

Test plan

• New BATS test: externally-created worktree found via porcelain fallback
• Full test suite passes (271 tests)
• Manual verification: git worktree add /tmp/ext -b ext-branch → git gtr go ext-branch succeeds
• Manual verification: without fix, same scenario fails with "Worktree not found"

Summary by CodeRabbit

• Bug Fixes
  • Improved worktree resolution to locate externally-created worktrees when initial lookup fails, enhancing fallback behavior and error handling.
• Tests
  • Added coverage validating the fallback lookup for external worktrees and the reported worktree attributes.

[coderabbitai]

Caution

Review failed

The pull request is closed.

Walkthrough

Adds a last-resort lookup in resolve_target that queries git worktree list --porcelain, parses entries to match a branch identifier, and emits a tab-separated line (is_main, path, branch) when found; preserves existing control flow if no match.

Changes

Cohort / File(s)	Summary
Core fallback logic lib/core.sh	Adds a porcelain-driven fallback in resolve_target: runs git worktree list --porcelain, iterates/parses entries to find a branch match, prints TSV (is_main<TAB>path<TAB>branch) and returns success; unchanged behavior if still not found.
Test coverage tests/core_resolve_target.bats	Adds a test that creates an external worktree and asserts resolve_target returns is_main=0, a path ending with the external suffix, and the expected branch via the porcelain fallback.

Sequence Diagram(s)

mermaid
sequenceDiagram
participant Caller
participant resolve_target
participant GitCLI
participant Filesystem
Caller->>resolve_target: request resolution for
resolve_target->>Filesystem: check managed worktrees directory
alt found in managed directory
Filesystem-->>resolve_target: match (is_main/path/branch)
resolve_target-->>Caller: return TSV match
else not found
resolve_target->>GitCLI: git worktree list --porcelain
GitCLI-->>resolve_target: porcelain entries
resolve_target->>resolve_target: parse entries, match branch
alt match found in porcelain
resolve_target-->>Caller: return TSV (is_main/path/branch)
else no match
resolve_target-->>Caller: error "Worktree not found"
end
end

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Poem

🐰
A branch once hidden, now I trot,
Through porcelain lines I trace the spot.
Main or linked, I sniff the trail,
A hop, a find — no worktree fails. 🥕

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: adding a fallback mechanism in resolve_target using git worktree list --porcelain to find worktrees.
Linked Issues check	✅ Passed	The PR implements the core requirement from #127: resolve_target now searches for worktrees outside the managed directory via git worktree list --porcelain, enabling it to find branches in the main working tree.
Out of Scope Changes check	✅ Passed	All changes are directly scoped to the stated objective: lib/core.sh adds the fallback lookup logic, and tests/core_resolve_target.bats adds corresponding test coverage.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fix/resolve-target-fallback-127

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