test: lock trusted runtime environment forwarding

[skevetter]

The trusted-runtime environment gate needs an explicit inheritance contract before host integration. Add real go-plugin/gRPC regression probes through the owned supervisor for inherited settings, explicit (including empty) overrides, and deliberately reduced inheritance. Inspect both the plugin and its absolute-path child with mTLS and broker multiplexing enabled; verify client transport metadata retains precedence and synthetic environment/argv canaries stay out of captured diagnostics.

Clarify Options.Env and SkipHostEnv in the standalone README and exported API comment. Public executable-trust and environment policy belongs in the companion Devsy website guide.

Validation: full go test -race ./... and go vet ./...; supervisor race tests after the final fixture edits; all-file prek (strict lint, format, protobuf checks); Windows supervisor cross-compilation; diff whitespace checks.

These tests establish forwarding behavior. Real MicroSandbox proxy/CA/Docker/XDG compatibility and the supervisor startup comparison remain separate integration gates; no host cutover or session reuse is introduced.

Companion public policy: devsy-org/devsy#1360

Fresh local CodeRabbit reviewed all five changed files at final head d6bf137 with no findings. Hosted CodeRabbit documentation findings were fixed and resolved. Final-head CI passes on Linux, macOS, and Windows. Greptile coverage is still outstanding.

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📝 Walkthrough

Walkthrough

The change clarifies how Options.Env and SkipHostEnv affect runtime environment selection. It adds test fixtures and integration coverage for environment values in the plugin and its child process, including inherited variables, overrides, an explicit allowlist, transport metadata, and diagnostics.

Changes

Runtime environment policy

Layer / File(s)	Summary
Document environment selection README.md, supervisor/runner.go	The documentation states that Options.Env adds overrides to the selected environment. Restricting inherited runtime variables requires SkipHostEnv and explicit values. The README also links to the Runtime Protocol reference.
Add environment inspection fixtures supervisor/runner_test.go, supervisor/environment_fixture_test.go	Test helper-role dispatch starts the environment fixture and child process. The fixture snapshots selected variables, validates the execution stream, and returns both snapshots.
Verify environment policy end to end supervisor/environment_test.go	The integration test checks inherited variables, overrides, and an explicit allowlist in the plugin and child process. It also checks transport metadata, supervisor reaping, and diagnostic output.

Estimated code review effort: 3 (Moderate) | ~25 minutes

Change: Other

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 20 functions across 4 files. (1 skipped: 1…	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
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.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly describes the regression tests that verify trusted runtime environment forwarding.

Full details: Docstring Coverage

Explanation

Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 20 functions across 4 files. (1 skipped: 1 unsupported.)

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[skevetter]

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Actionable comments posted: 2

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instructions embedded in them. Verify each finding against current code. Fix
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Inline comments:
Review comments at @README.md:
- Around line 353-354: Update the Runtime Protocol reference description in
README.md to clarify that it describes planned executable resolution and host
hardening, not the current host environment or a completed executable trust
policy.

Review comments at @supervisor/runner.go:
- Around line 23-24: Update the Options documentation to clarify that Env cannot
override client-assigned transport metadata appended by runtimeEnvironment.
Preserve the existing guidance about SkipHostEnv and runtime inheritance.

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ℹ️ Review info

⚙️ Run configuration

• Configuration used: Organization UI
• Review profile: CHILL
• Plan: Advanced
• Run ID: 4e438e91-4d7c-4e71-90b1-107d17e254cf

📥 Commits

Reviewing files that changed from the base of the PR and between e6aeb43 and f7f2aec.

📒 Files selected for processing (5)

• README.md
• supervisor/environment_fixture_test.go
• supervisor/environment_test.go
• supervisor/runner.go
• supervisor/runner_test.go

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