Stabilize runTrampoline unit tests

[dmerand]

What

Stabilize the runTrampoline unit tests in packages/app/src/cli/services/function/build.test.ts.

Why

main hit a timeout in runTrampoline > runs v1 trampoline on v1 module in this broken build. These tests were doing more setup than the code under test needs, which made them slower and more prone to flake.

How

• use a fixed wasm module path in the runTrampoline tests instead of constructing a full function extension
• mock binary existence checks so the tests skip download setup
• keep coverage on wasm import detection and the expected trampoline invocation

Testing

Re-run the previously failing macOS Node 20 CI lane and confirm it stays green.

Measuring impact

• n/a - this doesn't need measurement, e.g. a linting rule or a bug-fix

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes

[dmerand]

• Stabilize runTrampoline unit tests #7101 👈 (View in Graphite)
• main

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[github-actions]

We detected some changes at packages/*/src and there are no updates in the .changeset.
If the changes are user-facing, run pnpm changeset add to track your changes and include them in the next release CHANGELOG.

Caution

DO NOT create changesets for features which you do not wish to be included in the public changelog of the next CLI release.

[github-actions]

Coverage report

St.❔	Category	Percentage	Covered / Total
🟢	Statements	82.28%	15106/18360
🟡	Branches	74.85%	7453/9957
🟢	Functions	81.31%	3793/4665
🟢	Lines	82.67%	14283/17278

Test suite run success

3990 tests passing in 1527 suites.

Report generated by 🧪jest coverage report action from 9d01c5e

[Copilot]

Pull request overview

This PR aims to stabilize the runTrampoline unit tests in the function build test suite by removing reliance on dynamically created testFunctionExtension() instances and using a consistent module path/mocking setup.

Changes:

• Replaces per-test testFunctionExtension().outputPath usage in runTrampoline tests with a shared functionModulePath constant.
• Adds fileExists to the fs imports and mocks it to resolve true in beforeEach.

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[Copilot]

fileExists is imported here and later mocked in beforeEach, but the functions under test in this file (including runTrampoline) don’t call fileExists (they use readFileSync). Consider removing the fileExists import and its mock setup unless you’re intentionally asserting behavior that depends on it.