fix: update Python sidecar package guidance

[nanookclaw]

Summary

Closes #756.

The Python SDK auto-start failure message still pointed users at the old pmxtjs package. This updates the message to install pmxt-core while preserving the existing pmxt-server manual-start guidance, matching the current sidecar package naming used elsewhere in the project.

I also added a small source-level regression test under the Python SDK tests. It checks that the startup guidance includes npm install -g pmxt-core, keeps the pmxt-server hint, and no longer references pmxtjs in pmxt/client.py.

Verification:

• PYTEST_DISABLE_PLUGIN_AUTOLOAD=1 pytest tests/test_client_startup.py

Plain pytest tests/test_client_startup.py is blocked in my local environment before collection by a globally installed pytest plugin import error for evalcraft; the focused test above passes with external plugin autoload disabled.

[realfishsam]

PR Review: VERIFIED

What This Does

Fixes a stale package name in the Python SDK's auto-start failure error message: pmxtjs (the TypeScript npm package) was incorrectly told to Python users when the correct install target is pmxt-core (the sidecar server). Adds a source-level regression test to prevent the same mistake from recurring.

Blast Radius

• sdks/python/pmxt/client.py: error message text only — no behavioral change, no API surface touched
• sdks/python/tests/test_client_startup.py: new test file, no production impact
• No core logic, no generated files, no OpenAPI schema, no TypeScript SDK, no exchange normalizers touched

Consumer Verification

Before (base branch): A Python user whose sidecar fails to auto-start sees:

Failed to start PMXT server: ...

Please ensure 'pmxtjs' is installed: npm install -g pmxtjs
Or start the server manually: pmxt-server

pmxtjs is the TypeScript SDK — installing it does not provide the sidecar server. The advice is actively misleading.

After (PR branch): Same error path shows:

Failed to start PMXT server: ...

Please ensure 'pmxt-core' is installed: npm install -g pmxt-core
Or start the server manually: pmxt-server

pmxt-core is the correct sidecar package (confirmed by core/package.json "name": "pmxt-core" and the "pmxt-server" bin entry).

The fix is consistent with:

• sdks/typescript/pmxt/client.ts:337 — already pmxt-core
• sdks/typescript/pmxt/server-manager.ts:226 — already pmxt-core
• sdks/python/pmxt/server_manager.py:434 — already pmxt-core

Test Results

• Build: N/A (docs/message-only change)
• Unit tests: PASS — ran test_client_startup.py in clean environment, 1 passed
• Regression check: confirmed test fails against the unpatched file (pmxtjs in source → assertion pmxtjs not in source fails as expected)
• CI check runs: not available (PR from fork, no CI results recorded)

Findings

1. sdks/python/QUICKREF.py:8 — missed stale reference (non-blocking)
   The PR's own test asserts "pmxtjs" not in client_source — it scans client.py only. QUICKREF.py line 8 still says npm install -g pmxtjs under "Start Server:". This is the same category of bug the PR fixes and should be cleaned up (either in this PR or as immediate follow-up). It is a docstring/reference file not an error message, so it won't surface to users at runtime, but it will confuse developers reading the quick reference.

2. Test design (note, not blocking)
   test_client_startup.py scans source text rather than exercising runtime behavior. This is intentional and reasonable for catching stale string literals. The assert "pmxtjs" not in client_source assertion is appropriately broad — it will catch any future reintroduction of pmxtjs anywhere in client.py. One edge case: if the error message text is ever extracted to a module-level constant or moved to server_manager.py, the test would need updating, but that's a future maintenance concern, not a bug today.

PMXT Pipeline Check

• Field propagation (3-layer): N/A
• OpenAPI sync: N/A
• Financial precision: N/A
• Type safety: N/A
• Auth safety: N/A

Semver Impact

patch — error message wording only; no API surface, no response shape, no SDK behavior changed

Risk

The one remaining gap is QUICKREF.py:8. Everything else is clean. The fix is mechanically correct, parity with TypeScript and server_manager.py is confirmed, and the regression test works as intended.

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