Contain source-upgrade process trees

[chubes4]

Summary

• route source-upgrade child execution through the shared ControllerChildGuard containment primitive
• terminate remaining process-group members before reporting successful or failed root completion
• preserve nonzero, timeout, wait, and attach errors as primary while appending bounded cleanup diagnostics
• prove successful source commands cannot leave runnable background descendants

Verification

• cargo nextest run -p homeboy-upgrade source_upgrade_completion_reaps_background_process_group source_upgrade_timeout_terminates_the_entire_child_process_group --no-fail-fast passed repeatedly
• cargo nextest run -p homeboy-upgrade --no-fail-fast: 182/182 passed
• cargo check -p homeboy-upgrade
• cargo fmt --check
• git diff --check
• independent review: no actionable findings

Addresses the source-upgrade subcluster of #12008. The broader issue remains open for order-dependent engine/core/agent/lab failures that pass in isolated reproduction.

AI Assistance

OpenAI gpt-5.6-sol via OpenCode reproduced the process-tree cluster, isolated the divergent source-upgrade owner, implemented and reviewed the containment repair, and ran focused/package verification under human direction. Chris Huber remains responsible for every line.

[chubes4]

CI prerequisite update: this branch now includes the existing one-line AdoptArgs fixture commit from #11996 so current main can compile workspace tests and reach the focused process-tree tests. The source-upgrade repair remains independent; the prerequisite diff disappears when #11996 lands.

AI assistance: OpenAI gpt-5.6-sol via OpenCode identified and applied the existing prerequisite under human direction. Chris Huber remains responsible for the branch.

[homeboy-ci]

Homeboy Results — homeboy

Lint

✅ review lint — passed

ℹ️ Full options: homeboy self docs commands/lint
ℹ️ Save lint baseline: homeboy review lint homeboy --baseline
Deep dive: homeboy review lint homeboy --changed-since 66a6691

Artifacts and drill-down

• CI results artifact: homeboy-ci-results-homeboy-review-lint-homeboy-fast-Linux contains immediate command JSON for this action invocation.
• Observation artifact: homeboy-observations-homeboy-review-lint-homeboy-fast-Linux contains exported Homeboy run history for deeper queries.
• Drill-down: download the observation artifact, then run homeboy runs import <dir>, homeboy runs list, and homeboy runs findings <run-id>.
• Artifacts are attached to the workflow run: https://github.com/Extra-Chill/homeboy/actions/runs/31293722672

Audit

⚠️ review audit — no measurement

Deep dive: homeboy review audit homeboy --changed-since 66a6691

Artifacts and drill-down

• CI results artifact: homeboy-ci-results-homeboy-review-audit-homeboy-fast-Linux contains immediate command JSON for this action invocation.
• Observation artifact: homeboy-observations-homeboy-review-audit-homeboy-fast-Linux contains exported Homeboy run history for deeper queries.
• Drill-down: download the observation artifact, then run homeboy runs import <dir>, homeboy runs list, and homeboy runs findings <run-id>.
• Artifacts are attached to the workflow run: https://github.com/Extra-Chill/homeboy/actions/runs/31293722672

Tooling versions

• Homeboy CLI: homeboy 0.334.0+9ed09c21a203-dirty
• Extension: rust from https://github.com/Extra-Chill/homeboy-extensions
• Extension revision: 8f471080
• Action: unknown@unknown

[chubes4]

Superseded by #12012, which landed the verified source process-tree containment repair on main. AI assistance disclosure: OpenAI gpt-5.6-sol via OpenCode was used to verify patch equivalence and reconcile the PR queue.