Add automatic platform detection from scheme build settings

[jjfeiler]

Summary

When using session-set-defaults to configure a watchOS, tvOS, or visionOS scheme, the simulator build tools (build_sim, build_run_sim, test_sim) would incorrectly use "iOS Simulator" as the destination platform, causing build failures.

Problem

After setting session defaults with a Watch scheme:

session-set-defaults --scheme "MyApp Watch App" --simulatorName "Apple Watch Ultra 2"

Running build_sim would fail with:

Unable to find a device matching the provided destination specifier:
    { platform:iOS Simulator, OS:latest, name:Apple Watch Ultra 2 (49mm) }

The available destinations showed watchOS Simulator options, but the tool was hardcoded to use iOS Simulator.

Solution

This PR adds automatic platform detection by querying the scheme's build settings (SDKROOT and SUPPORTED_PLATFORMS) before building. The detected platform is then used to construct the correct destination string.

Changes

• New file: src/utils/platform-detection.ts - Utility function detectPlatformFromScheme() that:

  • Runs xcodebuild -showBuildSettings for the specified scheme
  • Parses SDKROOT and SUPPORTED_PLATFORMS to determine the target platform
  • Returns the appropriate XcodePlatform enum value (iOS Simulator, watchOS Simulator, etc.)

• Modified: src/mcp/tools/simulator/build_sim.ts - Calls platform detection before building

• Modified: src/mcp/tools/simulator/build_run_sim.ts - Calls platform detection before building

• Modified: src/mcp/tools/simulator/test_sim.ts - Calls platform detection before running tests

• Updated tests: Account for the additional platform detection call in mocked executors

Test plan

• All existing tests pass (1157 passed)
• Tested with iOS scheme - correctly uses iOS Simulator
• Tested with watchOS scheme - correctly uses watchOS Simulator
• Manual testing with tvOS and visionOS schemes (not tested, but follows same SDKROOT pattern)

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🤖 Generated with Claude Code

[coderabbitai]

Walkthrough

This pull request introduces automatic platform detection for Xcode simulator builds. A new platform detection utility queries xcodebuild settings to determine the target simulator platform (iOS, watchOS, tvOS, or visionOS) from the scheme's configuration. The build and test flows are updated to invoke this detection as an initial step, followed by the actual build command. Test files are refactored to expect the two-step command sequence, with updated assertions validating platform detection, build invocations, and corresponding log prefix labels for each stage.

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title directly and clearly summarizes the main change—adding automatic platform detection from scheme build settings—which is the core objective of the pull request.
Description check	✅ Passed	The description is comprehensive and directly related to the changeset, explaining the problem, solution, and changes made with concrete examples and test results.
Docstring Coverage	✅ Passed	Docstring coverage is 88.89% which is sufficient. The required threshold is 80.00%.

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