fix(auth): tighten Windows credentials ACL (#104)

[naufalfx805-source]

What does this PR do?

Closes #104.

This stops the Windows credentials path from silently relying on POSIX chmod(0o600), which Node cannot enforce on Windows ACLs.

Changes:

• On win32, ensureRestrictiveMode() now runs icacls with an args array: icacls <path> /inheritance:r /grant:r <USERNAME>:F.
• The POSIX chmod path remains unchanged for non-Windows hosts.
• If Windows ACL tightening cannot run, the CLI emits an explicit warning instead of silently pretending chmod protected the file.
• Adds unit coverage for the Windows ACL path using injected platform/spawn dependencies, so CI can verify this from any OS.

Verification

• npm test -- src/lib/credentials.test.ts -> 24 passed, 1 skipped
• npm run lint
• npm run typecheck
• npm run build
• git diff --check

Summary by CodeRabbit

• Bug Fixes
  • Improved credential-file permission tightening across platforms.
  • Added Windows support to apply restrictive ACLs to the current user when creating credentials.
  • Automatically warns when restrictive permissions cannot be applied (e.g., user lookup or permission command failure).
  • Kept the existing secure permission behavior for Unix-like systems.
• Tests
  • Added Windows-specific coverage for successful ACL tightening and warning scenarios.

[coderabbitai]

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro Plus

Run ID: ac1af55a-9256-4219-b423-6e84bfca113f

📥 Commits

Reviewing files that changed from the base of the PR and between 06b450e and b906cf2.

📒 Files selected for processing (1)

• src/lib/credentials.ts

🚧 Files skipped from review as they are similar to previous changes (1)

• src/lib/credentials.ts

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Walkthrough

Credential permission tightening now handles Windows through icacls ACL commands with injectable execution and warning callbacks, while retaining Unix chmod behavior. Tests cover successful Windows ACL invocation and failure warnings.

Changes

Credential permission enforcement

Layer / File(s)	Summary
Platform-aware permission tightening src/lib/credentials.ts	ensureRestrictiveMode accepts injectable runtime options, applies restrictive Windows ACLs through icacls, reports failures, and preserves Unix mode tightening.
Windows permission behavior tests src/lib/credentials.test.ts	Tests verify Windows ACL arguments and warning behavior when ACL tightening cannot execute.

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

Suggested reviewers: zeshi-du

Sequence Diagram(s)

sequenceDiagram
  participant CredentialsWriter
  participant ensureRestrictiveMode
  participant spawnSync
  participant WarningHandler

  CredentialsWriter->>ensureRestrictiveMode: tighten credentials file permissions
  ensureRestrictiveMode->>spawnSync: execute icacls with restrictive ACL arguments
  spawnSync-->>ensureRestrictiveMode: return execution status
  ensureRestrictiveMode->>WarningHandler: warn when username detection or ACL execution fails

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🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 60.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main change: tightening Windows credential ACLs.
Linked Issues check	✅ Passed	The PR tightens Windows ACLs with icacls, warns when enforcement can't run, and preserves the POSIX chmod path.
Out of Scope Changes check	✅ Passed	The changes stay focused on Windows credential permission handling and related tests.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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