test(executor-e2e): stage upload artifact fixtures

[Copilot]

Summary

The executor E2E harness emitted raw agent params for upload-build-attachment and upload-pipeline-artifact, but both executors consume the post-MCP staged Result shape. As a result, the scenarios failed during NDJSON parsing on missing staged_file and never exercised the upload paths.

• Staging helper

  • Added stagedSafeOutputFile() to mirror MCP staging metadata:
    • staged_file
    • file_size
    • staged_sha256
    • staged file contents

• Scenario updates

  • Updated both build upload scenarios to emit staged Result fields instead of params-only NDJSON.
  • Kept upload-workitem-attachment unchanged; it still reads file_path directly.

• Coverage

  • Added focused Vitest coverage for staged filename generation, UTF-8 byte sizing, and SHA-256 metadata.

ndjson: async (_ctx, state) => ({
  artifact_name: state.artifactName,
  ...state.staged.result,
})

Test plan

• cargo build
• npm test
• npm run typecheck
• npm run build:executor-e2e

[jamesadevine]

@copilot can you add tests for the negatives here e.g. incorrect sha256 is rejected

[Copilot]

@copilot can you add tests for the negatives here e.g. incorrect sha256 is rejected

Added negative coverage in 90b70ce: upload-pipeline-artifact now has a test that records the correct file size but an incorrect SHA-256 and asserts the executor rejects it with a SHA-256 mismatch.

[jamesadevine]

@copilot not a rust test, a test in the executor-e2e bundle!

[Copilot]

@copilot not a rust test, a test in the executor-e2e bundle!

Addressed in bc1e672: removed the Rust-only negative and added executor-e2e bundle coverage for upload-pipeline-artifact rejecting an incorrect staged_sha256.