[anth-volk]

Fixes #17

First of a stack of four pull requests that move Microcosm's upload transport into the emitter (plan step 2, E1 then H1). This one makes the emitter installable on its own and runnable as the build's child process. The next pull request adds the typed interface package whose client starts this command.

What changes

• microcosm-emitter command (microcosm_emitter.cli). uv tool install microcosm-emitter installs it outside the build's environment.
  • microcosm-emitter host --socket … --parent-pid … runs the existing service host, configured on standard input as before.
  • microcosm-emitter version prints the emitter version and accepted socket protocol versions as JSON.
• Started as the build's child, never as a service. The command is meant to be started exactly as today's launcher starts python -m microcosm_emitter.host (host/launcher.py:101): no separate environment, so it inherits the build's environment variables and user and finds the same Hugging Face credential (HF_TOKEN, then HUGGINGFACE_TOKEN, then the saved hf auth login token, core/auth.py:105–109). PR 2 adds the launcher and the test that proves this.
• Parent identification without psutil in the build. --parent-created-at is now optional. Without it, the host reads the named process's creation time and then checks again that the process is its own parent (os.getppid()); otherwise it refuses to start. A match after the read proves the creation time is the parent's, not that of an unrelated process given the same process ID after the parent exited. Launchers that pass the creation time behave as before.
• hello request. Only a host started by microcosm-emitter host answers {"action": "hello"}: with the emitter version, the accepted protocol versions (microcosm_emitter.compatibility.SUPPORTED_PROTOCOL_VERSIONS, now (1,)) and the loaded and skipped modules, typed as compatibility.HelloResponse. A host started with python -m microcosm_emitter.host (the in-process launcher) answers hello with an error, as for any unknown action.
• --skip-unavailable-modules starts the host without requested modules that this emitter does not install, so a newer build can still use an older emitter's modules. A request to a skipped module is refused like one to an unknown module, and the host still refuses to start if none of the requested modules is installed. Without the flag, a missing module still stops startup.
• python -m microcosm_emitter.host keeps working for Microcosm builds pinned to microcosm-emitter==0.2.1.
• README: a section on installing the emitter on its own.

Release

The fragment is added: merging releases the next minor version of microcosm-emitter to PyPI.

Validation

Red-green by commit (macOS, Python 3.14; only the test files this pull request adds or changes):

Commit	Red (tests first)	Green
3b33e27 Run the emitter host from an installed microcosm-emitter command	tests/host/test_installed_command.py, tests/test_package_names.py: 7 failed, 4 passed (2 existing tests, and 2 new guards for existing behaviour: python -m microcosm_emitter.host still starts, and hello without a description is refused)	11 passed; re-run after commit: 11 passed

ruff check and ruff format --check pass. CI runs the full suite.

Overlap with open pull requests

Max's #5, #6 and #7 also edit README.md; #5 also edits pyproject.toml (its dev dependencies, which this does not touch). Expect at most a small README rebase.

Review fixes (2026-10-20)

Each fix was written red, then green; only the test files this pull request adds or changes were run.

Commit	Finding	Red (tests first)	Green
8f599da Expect the missing-module error in the module selection test	test_module_selection_refuses_missing_and_duplicate expected "exactly one" for a missing module; load_module raises ModuleNotInstalledError. This was the CI failure on every pull request of the stack.	tests/host/test_runtime.py: 1 failed, 14 passed (as in CI)	15 passed
33c54d2 Read the parent's creation time before the final parent check	parent_process read create_time() after its only getppid() check.	tests/host/test_installed_command.py: 2 failed, 8 passed	10 passed
1ecadcf Let the parent-exit test see a host that outlives its parent	The test's short-lived build gave the host its standard error pipe, so subprocess.run(capture_output=True) returned only after the host exited and the final psutil.wait_procs assertion never ran. The build now gives the host no output pipes and reports its creation time.	Test-only fix. Against a host whose parent check always succeeds, the new test fails at "the host kept running after its parent exited" (1 failed); the old one failed only by a 30-second TimeoutExpired	Real host: 10 passed
22fca11 Type the hello payload and test skipped modules	README and fragment did not say that only microcosm-emitter host answers hello; no tests for --skip-unavailable-modules with every module missing or for a request to a skipped module; optional TypedDict.	The two skip tests passed against unchanged code (they guard existing behaviour: 11 passed); the TypedDict test failed (1 failed, 11 passed). README and fragment changes need no red step	12 passed

Re-run after the last commit: tests/host/test_installed_command.py, tests/host/test_runtime.py, tests/test_package_names.py: 30 passed. tools/check-quality.sh and tools/check-changelog.sh pass.

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