test(knowledge-base): isolate home expansion coverage

[mldangelo-oai]

Summary

• Follow up on fix(knowledge-base): expand ~ in --knowledge-base paths #254 without changing production behavior.
• Replace the persistent node:os module mock with a homedir spy restored after the test.
• Verify ~other paths remain unchanged without depending on the current working directory.

Verification

• Focused randomized knowledge-base tests: 8 passed, 0 failed.
• The same focused tests pass with a real ~other/docs/scope.md fixture in the working directory.
• Full randomized SDK suite: 1,032 passed, 11 expected skips, 0 failed (seed 12345).
• pnpm run types
• pnpm run format
• Codex code and security reviews found no issues.

[mldangelo-oai]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. You're on a roll.

Reviewed commit: d12422e243

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[chatgpt-codex-connector]

Security review completed. No security issues were found in this pull request.

Reviewed commit: d12422e243

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