Execute read-only git queries under --dry-run

[bkildow]

The bug

wt prune --dry-run reports No merged worktrees to prune. in every repository, no matter how many branches are actually merged. Found while trying to reclaim disk space across two projects that had 29 and 5 fully-merged worktrees respectively — dry-run insisted there was nothing to do in both.

--verbose shows the tell — the only git command is prefixed, meaning it never ran:

$ wt prune --dry-run --verbose
[dry-run] git --git-dir /…/.bare worktree list --porcelain
No merged worktrees to prune.

Why

cmd/prune.go:35 builds its Runner with IsDryRun(), and Run() returned "", nil without executing under dry-run. WorktreeList() goes through Run(), so it parsed empty output into a nil slice, the loop had nothing to iterate, and prune fell through to the "nothing to do" branch.

IsBranchMerged() had the mirror-image problem — it returned true unconditionally under dry-run. That one was masked: the worktree list was already empty, so it was never reached. Fix only the list and dry-run would have proposed pruning every worktree, merged or not.

Dry-run should suppress the changes, not the analysis that decides which changes to propose.

The change

Split Query() out of Run(). Query always executes and takes the read-only callers (WorktreeList, ListRemoteBranches, HasLocalBranch, GetDefaultBranch, ResolveStartPoint); Run keeps the dry-run gate for state-changing commands. IsWorktreeDirty, IsBranchMerged, GetLastCommitAge and GetBehindCount build their own exec calls, so their dry-run early-returns are just dropped.

This also fixes wt status, which reported unknown commit ages and 0 behind-counts under --dry-run.

Tests

TestDryRunMode covered these queries against a /nonexistent git dir and passed — for the wrong reason. The stubs meant the bogus path was never touched, so the test proved only that the stubs existed. Narrowed it to state-changing commands, where a fake git dir is the right tool.

Added TestDryRunExecutesQueries, which builds a real repo with one merged and one unmerged branch. Against main it fails all five assertions:

--- FAIL: TestDryRunExecutesQueries
    dry-run WorktreeList returned nothing; queries must execute under dry-run
    dry-run IsBranchMerged(unmerged, main) = true, want false
    dry-run HasLocalBranch(no-such-branch) = true, want false
    dry-run IsWorktreeDirty = false on a dirty tree
    dry-run GetLastCommitAge = "unknown", want a real relative date

go build, go vet, and the full suite pass on the branch.

Verified against real repos

Built the patched binary and re-ran the case that started this. Both counts match an independent git merge-base --is-ancestor sweep, and --dry-run still removed nothing:

$ wt prune --dry-run      # affiliated
→ Merged worktrees:
  issue/ADBUILD-1655-xss-member-news  …
  …29 total…

$ wt prune --dry-run      # newyorkcares-drupal
→ Merged worktrees:
  …5 total…
✓ Pruned 5 worktree(s)

https://claude.ai/code/session_01FyzmAG45hK4qPXFgVEbFHn