Auto-surface errors and failed tests on build failure

[conorluddy]

Summary

• On build/test failure, the top 5 errors and/or failed test details are now shown inline in the default minimal output
• Previously, agents saw only Build: FAILED (1 errors, 0 warnings) and needed a second round-trip with --get-errors to see actual error messages
• Success output is unchanged (zero token increase for passing builds)
• --verbose output unchanged
• --get-errors <id> still works for deeper drill-down
• JSON output on failure now includes errors and failed_tests arrays

Example output after this change

Build failure:

Build: FAILED (2 errors, 0 warnings) [xcresult-20260224-221804]

Errors (2):

1. Cannot find 'MyProtocol' in scope
   Location: /path/to/File.swift:line 135

2. Type 'ViewController' does not conform to 'Sendable'
   Location: /path/to/VC.swift:line 42

Test failure:

Tests: FAIL (11/12 passed, 4.2s) [xcresult-20260224-221804]

Failed tests (1):

1. LoginFlowTests/testInvalidCredentials
   XCTAssertEqual failed: ("Error") is not equal to ("Success")

Test plan

• Linting passes on all modified files
• --help still works
• Introduce deliberate build error in a test project, confirm errors appear inline
• Introduce deliberate test failure, confirm failed test details appear
• --json on failure includes errors array; on success, no errors key
• --verbose output unchanged

🤖 Generated with Claude Code