fix(policy): require github preset for git egress

[rluo8]

Summary

Remove system Git from the brew network policy so enabling Homebrew no longer implicitly grants Git access to GitHub. GitHub Git egress now requires the explicit github preset, restoring the intended least-privilege boundary.

Related Issue

Fixes #6502

Changes

• Remove /usr/bin/git from the brew preset while retaining Homebrew and curl access.
• Document that runtime Homebrew uses the baked-in installation and that GitHub Git access belongs to the github preset.
• Add a behavioral regression test over effective merged policies:
  • brew alone does not grant /usr/bin/git access to github.com:443.
  • brew with github does grant that access.
• Update the existing brew binary allowlist assertion and ratchet its legacy test-file size budget.

Type of Change

• Code change (feature, bug fix, or refactor)
• Code change with doc updates
• Doc only (prose changes, no code sample modifications)
• Doc only (includes code sample changes)

Quality Gates

• Tests added or updated for changed behavior
• Existing tests cover changed behavior — justification:
• Tests not applicable — justification:
• Docs updated for user-facing behavior changes
• Docs not applicable — justification: This restores the documented opt-in GitHub policy boundary; no user workflow or configuration syntax changes.
• Sensitive paths changed (security, policy, credentials, preflight, onboarding, inference, runner, sandbox, or messaging)
• Sensitive-path review completed or maintainer-approved waiver recorded — reviewer/approval link/justification:
• Non-success, skipped, or missing CI check accepted by maintainer — check name, approval link, and follow-up issue:

Verification

• PR description includes the DCO sign-off declaration and every commit appears as Verified in GitHub
• Normal pre-commit, commit-msg, and pre-push hooks passed, or npm run check:diff passed when hooks were skipped or unavailable
• Targeted behavior tests pass for the current change set, or tests are marked not applicable above — command/result or justification:
• Applicable broad gate passed — npm test for broad runtime/test-harness changes; npm run check for repo-wide validation/coverage changes — command/result:
• Quality Gates section completed with required justifications or waivers
• No secrets, API keys, or credentials committed
• npm run docs builds without warnings (doc changes only)
• Doc pages follow the style guide (doc changes only)
• New doc pages include SPDX header and frontmatter (new pages only)

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Signed-off-by: Rui Luo ruluo@nvidia.com

Summary by CodeRabbit

Summary

• Bug Fixes

  • Updated the Homebrew policy preset to exclude system Git binaries by default (so GitHub Git access requires the GitHub preset).

• Tests

  • Added coverage ensuring GitHub github.com:443 egress for Git is denied with only the Homebrew preset, and permitted when Homebrew + GitHub presets are both active.
  • Updated Homebrew filesystem read/write whitelist expectations to remove /usr/bin/git and include the Homebrew-managed ~/.linuxbrew/bin/brew path.

• Chores

  • Adjusted the test file size budget expectation.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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Configuration used: Path: .coderabbit.yaml

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📥 Commits

Reviewing files that changed from the base of the PR and between 9d1c3a7 and 0aee7ec.

📒 Files selected for processing (1)

• ci/test-file-size-budget.json

✅ Files skipped from review due to trivial changes (1)

• ci/test-file-size-budget.json

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📝 Walkthrough

Walkthrough

The brew preset removes /usr/bin/git from its allowed binaries. Existing policy expectations and the file-size budget were updated, and a new test checks that GitHub git access only appears when both brew and github presets are active.

Changes

Brew preset git access boundary fix

Layer / File(s)	Summary
Brew preset binary allowlist change nemoclaw-blueprint/policies/presets/brew.yaml	Removes /usr/bin/git from the brew preset binary allowlist and adds a comment about excluding system git for git-based Homebrew operations.
Existing policy test updated for new allowlist test/policies.test.ts, ci/test-file-size-budget.json	Updates the brew preset expectation list to include ~/.linuxbrew/bin/brew, removes /usr/bin/git, and adjusts the file-size budget entry for test/policies.test.ts.
New GitHub access boundary test test/brew-github-policy-boundary.test.ts	Adds helpers to merge presets and detect GitHub git egress, then asserts brew alone denies it while brew plus github allows it.

Estimated code review effort: 2 (Simple) | ~10 minutes

Sequence Diagram(s)

sequenceDiagram
  participant Test as brew-github-policy-boundary.test.ts
  participant Resolver as resolveEffectivePolicy
  participant PresetLoader as policy preset loader
  participant Checker as allowsGitToReachGitHub

  Test->>Resolver: resolveEffectivePolicy(["brew"])
  Resolver->>PresetLoader: load brew preset
  PresetLoader-->>Resolver: brew policy entries
  Resolver-->>Test: effective policy
  Test->>Checker: inspect network_policies
  Checker-->>Test: false

  Test->>Resolver: resolveEffectivePolicy(["brew","github"])
  Resolver->>PresetLoader: load brew preset
  PresetLoader-->>Resolver: brew policy entries
  Resolver->>PresetLoader: load github preset
  PresetLoader-->>Resolver: github policy entries
  Resolver-->>Test: merged effective policy
  Test->>Checker: inspect network_policies
  Checker-->>Test: true

Loading

Suggested labels: area: sandbox, bug-fix

Suggested reviewers: ericksoa, kjw3

🚥 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 summarizes the main change: requiring the github preset for GitHub git egress.
Linked Issues check	✅ Passed	[#6502] The changes remove git from the brew preset and add tests showing GitHub egress only works when github is explicitly enabled.
Out of Scope Changes check	✅ Passed	The added test and file-size-budget tweak are directly tied to the policy fix and do not introduce unrelated changes.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

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[coderabbitai]

Actionable comments posted: 2

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@test/brew-github-policy-boundary.test.ts`:
- Around line 20-31: The test helper allowsGitToReachGitHub is re-implementing
policy matching instead of using the real sandbox policy logic. Update the test
to exercise the actual src/lib/policy evaluator/enforcer used at runtime, and
assert its result for the GitHub/git case rather than parsing YAML and checking
host/port/binary fields manually. If needed, replace the custom predicate with a
call into the production policy API so the test stays aligned with enforcement
semantics.
- Around line 33-47: The new guard checks in resolveEffectivePolicy add two if
statements that violate the test-conditionals limit. Replace those fail-fast
checks with assertion-based validation in the same function, keeping the logic
around policies.loadPreset, policies.extractPresetEntries, and
policies.mergePresetIntoPolicy but removing explicit if/throw branches.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

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Run ID: 4dafa802-be38-49ac-90e3-0463082bbff6

📥 Commits

Reviewing files that changed from the base of the PR and between e962d05 and c5dff46.

📒 Files selected for processing (4)

• ci/test-file-size-budget.json
• nemoclaw-blueprint/policies/presets/brew.yaml
• test/brew-github-policy-boundary.test.ts
• test/policies.test.ts

💤 Files with no reviewable changes (1)

• test/policies.test.ts