v1.57.4.0 fix(setup): route gen:skill-docs through bun_cmd; drop tail -3 pipe that masks bun failures

[DavidMiserak]

Summary

Fix two bugs in setup that silently broke skill doc generation on certain installations.

bun_cmd routing fix — Three helpers (link_codex_skill_dirs, link_factory_skill_dirs, link_opencode_skill_dirs) called literal bun run gen:skill-docs instead of the bun_cmd wrapper. The bun_cmd wrapper exists to handle Windows non-ASCII usernames: prepare_bun_for_windows_compile copies bun to an ASCII path and points BUN_CMD at it when needed. Bypassing it caused silent failures on affected installs. (setup:714, 919, 951)

Pipe-masking exit-code fix — The gbrain-detected SKILL.md regen ran bun_cmd run gen:skill-docs:user ... 2>&1 | tail -3. The pipe makes the subshell's exit status tail's, which is always 0, so the trailing || log "warning..." guard never fired when bun failed. Dropping the pipe restores correct failure detection. (setup:1297)

Both fixes were identified by @jbetala7 during review on #1883, carved out as a focused fast-merge PR per their request.

Test Coverage

CODE PATHS
[+] setup (shell script)
  ├── link_codex_skill_dirs()
  │   ├── [★★★ TESTED] bun_cmd invoked via $BUN_CMD — test:4
  │   └── [★★★ TESTED] uses bun_cmd, not bare bun — test:5
  ├── link_factory_skill_dirs()
  │   └── [★★★ TESTED] uses bun_cmd, not bare bun — test:5
  ├── link_opencode_skill_dirs()
  │   └── [★★★ TESTED] uses bun_cmd, not bare bun — test:5
  └── gbrain regen block (setup:1295-1298)
      ├── [★★★ TESTED] without pipe → || warning fires — test:1
      ├── [★★★ TESTED] with pipe (bug shape) → warning silent — test:2
      └── [★★★ TESTED] live block has no pipe — test:3

COVERAGE: 6/6 paths tested (100%)

Tests: 0 → 5 (+5 new)

Pre-Landing Review

Review: CLEAR (DIFF, 2026-06-08, same commit). Quality score: 9.0/10.

0 critical. 4 informational (all skipped — minor test quality suggestions, no blocking issues).

Adversarial: Pre-existing set -e dead-code in warning blocks (not introduced by this PR). Recommendation: ship as-is.

Design Review

No frontend files changed — design review skipped.

Eval Results

No prompt-related files changed — evals skipped.

Greptile Review

No Greptile comments.

Scope Drift

Scope Check: CLEAN — 4 setup lines + 5 tests + CHANGELOG/VERSION, no creep.

Plan Completion

No plan file detected.

TODOS

No TODO items completed in this PR.

Test plan

• bun test test/setup-bun-cmd-and-pipe-bugs.test.ts — 5 pass / 0 fail
• bun test — exit code 0 (pre-existing failures in E2E/browse suites unrelated to this branch)
• bash -n setup — syntax OK

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[jbetala7]

Verified on main — both fixes are real and this is exactly the carve-out we discussed on #1883:

• link_codex/factory/opencode_skill_dirs call literal bun run gen:skill-docs at setup:714/919/951, while the sibling install paths (setup:454/464/474) correctly use bun_cmd. On a non-ASCII Windows username the literal bun can't resolve the unicode path, the call exits nonzero, and the [ ! -d "$…_dir" ] guard immediately after silently proceeds as if generation succeeded. Switching those three to bun_cmd matches the rest of the function.
• the | tail -3 on the gbrain gen:skill-docs:user regen (setup:1297) masks the pipeline exit status, so a failed regen still reports success and the || log "warning…" branch never fires. Dropping it restores real failure detection.

Scope is tight (4 setup lines + a focused regression test), no phase restructure, no Playwright behavior change. Looks correct to me.