fix: subprocess probes inherited a relative BUNDLE_GEMFILE and broke on chdir

[pftg]

Master has been red for six consecutive commits on Test Ruby & Rails (3.3, rails81_gems.rb, false). This unblocks the release.

What broke

Six probe tests die with:

/tmp/d20260824-4743-risnub/gemfiles/rails81_gems.rb not found (Bundler::GemfileNotFound)
	from /opt/.../rubygems.rb:1397:in `<top (required)>'
	from <internal:gem_prelude>:2:in `<internal:gem_prelude>'

All six route through one helper, GemNameEntryPointTest.probe, which spawns a bare ruby with chdir: a tmpdir and passed no env — so the child inherited BUNDLER_SETUP. RubyGems ends rubygems.rb with:

require ENV["BUNDLER_SETUP"] if ENV["BUNDLER_SETUP"] && !defined?(Bundler)

The child therefore re-enters bundler/setup before it reaches -e, and resolves the workflow's relative BUNDLE_GEMFILE: gemfiles/rails81_gems.rb against its cwd — the tmpdir.

Why only ruby 3.3, and why never locally

Bundler >= 2.6 rewrites BUNDLE_GEMFILE to an absolute path during setup; the 2.5 that ships with ruby 3.3 leaves it alone. Measured:

ruby	BUNDLE_GEMFILE after require "bundler/setup"
3.3.12 (bundler 2.5)	gemfiles/rails81_gems.rb — relative, breaks
4.0.6 (bundler 2.7)	/abs/path/gemfiles/rails81_gems.rb

bundle exec expands it too, which is why every local run was green. The 3.3/rails81 cell failed first and fail-fast cancelled the other 3.3 cells — they were not passing, just unreported.

This is the repo's own documented rule applied by halves: a subprocess probe of a tree it built itself must chdir out of the project and scrub the bundle. The chdir landed; the scrub did not.

The fix — class, not instances

• PROBE_ENV in test_helper.rb is now the single child environment for probes that chdir out of the project: BUNDLER_SETUP, BUNDLE_GEMFILE, RUBYLIB, RUBYOPT. legacy_deletion_test.rb had hand-rolled three of the four (missing BUNDLER_SETUP) and now shares it.
• Scrub vs absolutise, decided per probe. Every probe that spawns bare ruby with its own -I load paths wants no bundler at all → scrub. Every probe that chdir: PROJECT_ROOT genuinely wants the bundle, and a relative BUNDLE_GEMFILE resolves fine from there → left alone. A relative BUNDLE_GEMFILE stays a legitimate thing for a workflow to set, so .github/workflows/test.yml is unchanged.
• NO_BUNDLE_GATE opens every probe and aborts if the bundle leaked in. Without it the scrub could silently stop working and stay green on every ruby but 3.3 — exactly how this reached master six times.
• The gate is tested against the opposite condition: restoring BUNDLER_SETUP alone must make the same probe refuse to run.

Verification

Mutation — reverting the scrub, under a CI-shaped env (relative BUNDLE_GEMFILE), reproduces the CI trace exactly:

bundler/definition.rb:38: /var/folders/.../T/d20260824-32758-8r245p/gemfiles/rails81_gems.rb not found (Bundler::GemfileNotFound)
	from rubygems.rb:1459:in '<top (required)>'
	from <internal:gem_prelude>:2
4 runs, 4 failures

The same mutation under a plain local run — where the old code was silently green — now fails loudly:

GATE: the probe inherited the development bundle, so it proves nothing

That is the hole this closes. Restore verified byte-identical (sha256 5b6ac333… before and after).

Green both ways: rake test:unit 720 runs / 0 failures normally and with the env CI uses (CI=true + relative BUNDLE_GEMFILE); rake test:canonical 610 runs / 0 failures; standardrb lib test 161 files, no offenses.

No version.rb or CHANGELOG.md changes.

🤖 Generated with Claude Code

https://claude.ai/code/session_014BQJX6eWzBj2UTm5zQsjEs

Summary by Sourcery

Prevent subprocess probes from inheriting the development bundle when they run from temporary or deleted project trees.

Bug Fixes:

• Prevent subprocess probes from inheriting the development Bundler environment when running outside the project, avoiding failures caused by relative bundle paths after chdir.
• Share consistent environment cleanup across subprocess probes, including legacy deletion checks.

Enhancements:

• Add a subprocess guard that fails loudly when a probe accidentally runs with Bundler loaded.
• Add coverage verifying that the guard rejects an inherited Bundler setup before executing probe code.

Tests:

• Add regression coverage for rejecting leaked Bundler state in subprocess probes.

Summary by CodeRabbit

• Bug Fixes

  • Improved validation for commands run outside the project directory, preventing inherited development environment settings from affecting results.
  • Added safeguards to detect and reject improperly configured subprocess environments before execution.

• Tests

  • Expanded automated coverage for environment isolation and legacy project-tree scenarios.
  • Updated probe guidance to ensure reliable behavior when working with removed or isolated project files.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 60a82b62-f6fe-4adb-86f7-8d5741b784d4

📥 Commits

Reviewing files that changed from the base of the PR and between 75cf9f9 and bf694c1.

📒 Files selected for processing (3)

• test/test_helper.rb
• test/unit/gem_name_entry_point_test.rb
• test/unit/legacy_deletion_test.rb

Included review availability: Your plan provides up to 1 included review per hour; 0 remain after this review.

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📝 Walkthrough

Walkthrough

Subprocess probes now use a shared environment that removes Bundler and project load-path settings. The probe helper adds a no-Bundler gate. Legacy deletion probes merge their deleted-tree setting into the shared environment, with coverage for inherited Bundler setup.

Changes

Probe isolation

Layer / File(s)	Summary
Shared probe environment contract test/test_helper.rb	Defines frozen PROBE_ENV overrides for Bundler and Ruby load-path settings.
Probe execution gate and validation test/unit/gem_name_entry_point_test.rb, test/unit/legacy_deletion_test.rb	Passes the environment to subprocess probes, rejects probes when Bundler is loaded, and applies PROBE_ENV to legacy deletion probes. Tests cover inherited BUNDLER_SETUP rejection.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: ⚪ Minimal · up to bf694

The change isolates test subprocesses from inherited bundle settings and adds regression coverage; no actionable merge-blocking risk remains after normal checks and review.

🚥 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 clearly identifies the main fix: preventing subprocess probes from inheriting a relative BUNDLE_GEMFILE when changing directories.
Docstring Coverage	✅ Passed	Docstring check was indeterminate for this PR — some files could not be analyzed in time. Not blocking.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/probe-env-under-ci

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Reviewer's Guide

Fix subprocess probes that chdir into temporary or deleted trees by scrubbing inherited Bundler and Ruby environment variables, while adding an executable gate and regression test to ensure probes cannot silently validate the wrong environment.

File-Level Changes

Change	Details	Files
Centralize subprocess environment isolation for probes that run outside the project tree.	Define a frozen environment scrubber removing Bundler and Ruby load-path variables. Reuse the scrubber in the legacy deleted-tree probe instead of maintaining a partial copy. Keep probes rooted at the project directory on the inherited bundle because they intentionally exercise it.	test/test_helper.rb test/unit/legacy_deletion_test.rb
Prevent probes from silently running under the development bundle and add regression coverage for the original failure mode.	Inject a child-process gate that aborts if Bundler is already loaded. Apply the gate and scrubbed environment to gem-name entry-point probes. Add a test that restores BUNDLER_SETUP and verifies the gate aborts before executing the probe body.	test/unit/gem_name_entry_point_test.rb

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