[HOLD FOR INTAKE] feature AIENG-624: add --from-github-actions option to subset command

[mnamachivayam]

Summary

Adds a --from-github-actions flag to smart-tests subset, selecting the GitHub App flow where the server creates the build and test session implicitly from the GitHub Actions environment instead of the client passing a --session.

This unblocks GitHub App users, for whom commit/file-change data isn't available at subset time and test sessions were always created in Observation Mode — so real subsetting never occurred.

With the flag set, the CLI detects GITHUB_RUN_ID, GITHUB_RUN_ATTEMPT, GITHUB_REPOSITORY, GITHUB_JOB and RUNNER_NAME and sends them in the subset payload (fromGithubActions, githubActionsRunId, githubActionsRunAttempt, githubActionsJobName, githubActionsRunnerName, repositoryOwner, repositoryName), so the server can resolve commit and file change data via the GitHub API and subset in non-Observation mode.

- name: Run tests with Smart Tests
  run: |
    smart-tests subset --from-github-actions maven --target 80% src/test/java > subset.txt
    mvn test -Dsurefire.includesFile=subset.txt

Flag behaviour

Invocation	Result
--from-github-actions, no --session	GitHub App flow
--session only	classic flow, unchanged
both	error (contradictory intent)
neither	error (existing behaviour)
--from-github-actions outside GitHub Actions	error
--from-github-actions with a missing/malformed variable	error naming the variable
--from-github-actions --non-blocking	warning; --non-blocking ignored

Test plan

• 6 new tests covering the GitHub App payload, the --session conflict, running outside GitHub Actions, a missing variable, a malformed GITHUB_REPOSITORY, and the no-flag/no-session error
• Full suite: 497 tests pass
• flake8 and mypy clean
• Manually exercised the flow and each error path against the CLI

🤖 Generated with Claude Code

[Konboi]

LGTM

[Konboi]

👍