Report a missing registry file without a traceback

[dmccoystephenson]

Summary

• main() in src/arcade/__main__.py now catches OSError alongside registry.RegistryError, so a registry path that does not exist or cannot be read is reported by routers, hosts, check-registry and serve as a single arcade: <message> line on stderr instead of a Python traceback. The exit status stays 1, so scripts are unaffected.
• For serve, RegistryHolder.refresh(initial=True) already re-raises the OSError on first load before anything binds; that error now reaches the same one-line report. A side effect worth noting: any other OSError escaping a handler (for example a bind failure such as "Address already in use" in makeServer) is also printed as one arcade: ... line with exit 1 rather than a traceback.
• Regression tests added in tests/test_main.py: test_a_missing_registry_is_reported_without_a_traceback (parametrized over routers, hosts, check-registry) and test_serve_refuses_a_missing_registry_before_binding.
• CHANGELOG.md: a ### Fixed entry under ## [Unreleased]. __version__ is unchanged.

Closes #1

Test plan

• python3 -m pytest -q: 149 passed locally (Python 3)
• Regression check: with the __main__.py fix stashed, the 4 new test cases fail; with it restored, they pass
• CI: test (3.8), test (3.12), docker
• PYTHONPATH=src python3 -m arcade check-registry examples/games.yaml and black --check could not be run locally in this sandbox. CI runs check-registry, and the diff does not touch the example registry or the parser. The new code was written to black's 110-column style by hand.

No other open issues existed at triage, so none were skipped.

This PR description was drafted during a Gardener session (https://github.com/Stephenson-Software/gardener).

🤖 Generated with Claude Code

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drafted by Claude on behalf of Daniel Stephenson

[dmccoystephenson]

Self-review rubric (scored against CI run 37757498918 on the PR head and the diff):

• Scope: PASS. Three files changed (src/arcade/__main__.py, tests/test_main.py, CHANGELOG.md), each required by CLI prints a traceback when the registry file is missing #1. No formatting or rename churn.
• Tests-new: PASS. No new public function was added. The one changed behavior (main()'s except clause) is exercised by 4 new test cases.
• Tests-fix: PASS. With src/arcade/__main__.py stashed, pytest tests/test_main.py -k missing gave 4 failed. With it restored, 4 passed.
• Sibling structure: PASS. The new tests follow test_an_invalid_registry_is_reported_without_a_traceback and test_serve_refuses_an_invalid_registry_before_binding: same fixtures, same assertions on stderr prefix and empty stdout.
• Sibling renames: PASS. Nothing was renamed.
• Docs: PASS. The README does not describe CLI error output, so the only doc that changes is the CHANGELOG ### Fixed entry under ## [Unreleased].
• Issue resolution: PASS. CLI prints a traceback when the registry file is missing #1 names main()'s except clause and asks for a test in tests/test_main.py. Both are in the diff, and serve is covered too.
• CI: PASS. test (3.8), test (3.12) and docker all pass.
• Stdlib-only: PASS. No import lines were added.
• Py3.8: PASS. Only a tuple in an except clause was added, and test (3.8) is green.
• Vendored client untouched: PASS. trace_client.py is not in the diff.
• Naming: PASS. Only test-local missing and argv were added.
• Isolation headers: n/a. No server.py response path changed.
• Config documented / CLI documented: n/a. No ARCADE_* variable, subcommand or flag was added.
• Changelog: PASS. An entry was added under ## [Unreleased], and __version__ is unchanged.

Points for the reviewer:

• src/arcade/__main__.py:145: catching OSError covers more than the registry read. Any OSError that escapes a handler, such as a bind failure ("Address already in use") from makeServer in serve, now also prints as one arcade: ... line with exit 1 rather than a traceback. This seems a reasonable improvement in the same direction, but the change is wider than the issue's literal wording.
• black --check and the local check-registry examples/games.yaml invocation could not be run in this sandbox. CI covers check-registry. Black is not enforced in CI, and the added lines are under 110 columns.
• Out of diff: CHANGELOG.md has no ## [0.6.1] / ## [0.6.2] sections while __version__ is 0.6.3.dev0 and the 0.6.2 release is referenced in history. A separate issue was filed for this rather than editing release sections here.

None of the changed paths is on the do-not-auto-merge list. Merging was not authorized for this dispatch, so the PR is left for a maintainer.

This review was drafted during a Gardener session (https://github.com/Stephenson-Software/gardener).

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drafted by Claude on behalf of Daniel Stephenson