Problem

Running lint from a worktree under ~/pub/cli.worktrees/* intermittently fails with phantom lint issues pointing at file paths in other worktrees — including deleted ones (failed to parse file … no such file or directory).

golangci-lint keys its results cache on file contents but stores each cached issue's absolute path. Two worktrees with byte-identical packages (the near-static tools/ module is the usual culprit) get a cross-worktree cache hit in the machine-global ~/Library/Caches/golangci-lint, so the second worktree inherits the first's absolute paths. The //nolint post-processor then re-opens those paths to apply suppressions; when the other worktree has been deleted the open fails, so suppressed issues (e.g. dupword) leak through as phantom failures.

Upstream: this is golangci/golangci-lint#6656, closed as an accepted trade-off (won't-fix, no opt-out flag shipped) of the shared-cache work in #6445 ("decrease cache entropy", which dropped the path from the cache key in v2.12.0). The maintainer's position: "the core of linters is required absolute paths." A commenter reproduced the exact //nolint-leak variant. #6445 also notes concurrent cross-worktree runs on the shared cache are unsafe (file races).

Fix

Set GOLANGCI_LINT_CACHE to a per-worktree path ({{.ROOT_DIR}}/.task/golangci-lint) in a top-level env: block, so the cache lives under each worktree's already-gitignored .task/. No two worktrees can share it → contamination is structurally impossible.

Verified with disposable worktrees (create A → lint → delete A → lint identical B): 3 phantom dupword failures before, 0 issues after. CI is unaffected: the lint job runs a single clean checkout and never persists this directory (setup-go caches only the Go build cache).

Performance trade-off (measured)

Isolation removes cross-worktree cache reuse, so a fresh worktree's first full lint runs cold. Measured on the root module with the shared go-build cache kept warm (only golangci-lint's own issues cache is affected):

So the penalty only hits full task lint / full / all. The everyday ./task loop (lint-q, changed files only) is unaffected.

Two mitigations for developers with many worktrees:

• Opt-out: Task's env: yields to an inherited value, so export GOLANGCI_LINT_CACHE=~/Library/Caches/golangci-lint restores cross-worktree reuse with no Taskfile edit.
• task seed-lint-cache: copies the main worktree's cache into the current one so the first full lint runs warm (~4s in testing). Safe because the main worktree is permanent, so its cached issue paths always resolve; no-ops when GOLANGCI_LINT_CACHE is overridden.

Testing

Reproduced the failure and confirmed the fix, the opt-out precedence, and the seed task end-to-end using disposable detached worktrees. yamlfmt -lint clean.

This pull request and its description were written by Isaac.