fix(picker): stash collect warnings until skim releases the terminal

[max-sixty]

Summary

collect::collect emits warnings on stderr (stale default branch, batch-fetch failure, drain timeout, per-row task errors). On the wt list path that's fine. On wt switch, collect runs on a background thread while skim's TUI owns the terminal — eprintln overlays the rendered frame and corrupts skim's clear math, leaving fragments visible after the user picks.

Reproducer (synthetic picker-test repo with a stale worktrunk.default-branch set):

▲ Configured default branch ghost-branch does not exist locally
↳ To reset, run wt config state default-branch clear

…appears overlaid on picker rows mid-render.

Approach

Warnings flow through a new PickerProgressHandler::stash_warning. The picker holds an Arc<Mutex<Vec<String>>> shared with its handler, collect appends from the bg thread, and the picker drains and emits the lines after Skim::run_with returns (and in the dry-run path after the bg thread joins). Late warnings still in flight on the bg thread fall on the floor with the thread, per the existing "don't join after skim" rule.

wt list's stderr behavior is unchanged — when progressive_handler is None, the same closure writes straight to stderr.

The drain-timeout warning + hint that previously hardcoded wt list is now subcommand-agnostic and follows writing-user-outputs patterns: "Listing worktrees timed out after Xs", command at end of clause, semicolon between alternatives, -vv last.

Test infrastructure

Three small extractions made the new code testable end-to-end and brought patch coverage up from 66.7% to 100%:

• drain_stashed_warnings(&Mutex<Vec<String>>) in picker/mod.rs — both drain call sites collapse to one line; helper body has dedicated unit tests.
• format_drain_timeout_diag(received_count, &items) in collect/mod.rs — pure formatter; snapshot-tested for the no-blocked and blocked-items paths.
• handle_drain_timeout(drain_outcome, collect_deadline, &emit) in collect/mod.rs — wraps the previously-untestable DrainOutcome::TimedOut branch (DRAIN_TIMEOUT is 120s with no test seam). Three unit tests synthesize DrainOutcome values directly to cover all branches: timeout-fires, intentional-truncation, complete-outcome.

Plus a new integration test in switch_picker_dry_run.rs that runs the picker in dry-run mode against a stale worktrunk.default-branch and asserts the warning + reset hint reach stderr after the bg thread joins.

Test plan

• cargo run -- hook pre-merge --yes — 3508 tests pass, pre-commit clean (8 new tests across the helpers above).
• wt list warning snapshot tests still pass — non-picker stderr unchanged.
• Manual repro: WORKTRUNK_PICKER_DRY_RUN=1 wt switch --no-cd against picker-test with a stale default branch now surfaces both warning lines on stderr after the picker exits.

This was written by Claude Code on behalf of @max-sixty

[worktrunk-bot]

codecov/patch failed at 66.7%. The misses split into three groups:

src/commands/list/collect/mod.rs:641-642 — the picker-handler branch of the new emit_warning closure (h.stash_warning(line)). The non-picker branch on line 643 is covered, but no test runs collect::collect with progressive_handler: Some(...) and a warning trigger. This is the most reachable gap — a focused unit test that wires a mock PickerProgressHandler through collect with a stale-default-branch repo would cover it.

src/commands/list/collect/mod.rs:1419-1424 — the drain-timeout warning emission (Listing worktrees timed out after Xs + the -v/-vv hint). DRAIN_TIMEOUT is 120s with no test seam, so this path was already untested on main; codecov flags it now because the lines were rewritten from eprintln! to emit_warning(...) (new lines from its perspective).

src/commands/picker/mod.rs:672, 693 — the dry-run and post-skim drain loops. Picker integration tests use WORKTRUNK_PICKER_DRY_RUN=1 and don't trigger any warning-producing condition during collect, so the loop body never executes. Difficult to cover without a heavier picker harness.

Dismissing approval per CLAUDE.md (codecov/patch is mandatory). Happy to push a unit test for the first gap if useful.

[worktrunk-bot]

codecov/patch failed at 66.7%. The misses split into three groups:

src/commands/list/collect/mod.rs:641-642 — the picker-handler branch of the new emit_warning closure (h.stash_warning(line)). The non-picker branch on line 643 is covered, but no test runs collect::collect with progressive_handler: Some(...) and a warning trigger. This is the most reachable gap — a focused unit test that wires a mock PickerProgressHandler through collect with a stale-default-branch repo would cover it.

src/commands/list/collect/mod.rs:1419-1424 — the drain-timeout warning emission (Listing worktrees timed out after Xs + the -v/-vv hint). DRAIN_TIMEOUT is 120s with no test seam, so this path was already untested on main; codecov flags it now because the lines were rewritten from eprintln! to emit_warning(...) (new lines from its perspective).

src/commands/picker/mod.rs:672, 693 — the dry-run and post-skim drain loops. Picker integration tests use WORKTRUNK_PICKER_DRY_RUN=1 and don't trigger any warning-producing condition during collect, so the loop body never executes. Difficult to cover without a heavier picker harness.

Dismissing approval per CLAUDE.md (codecov/patch is mandatory). Happy to push a unit test for the first gap if useful.

codecov/patch failed — see follow-up review for analysis

[worktrunk-bot]

codecov/patch failed at 92.85% (5 misses out of 70 changed lines). All remaining uncovered lines are the call site of format_drain_timeout_diag inside the DrainOutcome::TimedOut branch (src/commands/list/collect/mod.rs:1428-1434):

1428: let diag = format_drain_timeout_diag(received_count, &items_with_missing);
1429: emit_warning(warning_message(&diag).to_string());
1430: emit_warning(
1432:     "A git command likely hung; for details, re-run with -v; ..."
1434:     .to_string(),

The pure function itself is now covered by the two new snapshot tests; the gap is the same pre-existing untestable path the prior review flagged — DRAIN_TIMEOUT is 120s with no seam to fire the branch synthetically. Picker (drain_stashed_warnings, stash_warning) and the picker-handler branch of emit_warning are at 100%.

Dismissing my approval per CLAUDE.md (codecov/patch is mandatory). Options to clear the check: refactor the drain-timeout block into a helper that takes drain_outcome + emit_warning and unit-test it against a synthetic DrainOutcome::TimedOut, or accept the gap and merge with explicit approval.

codecov/patch failed at 92.85% — 5 lines uncovered in the drain-timeout call site