Fix nats-core type issues

[caspervonb]

• Fix error callback type to accept Exception | str
• Fix _handle_info parameter type to use ProtocolServerInfo
• Use isinstance narrowing for protocol message unions
• Fix JWT auth type narrowing in _setup_jwt_auth
• Fix minor type issues in tests and bench tool
• Remove unused type: ignore comments

[Copilot]

Pull request overview

This PR focuses on resolving typing issues across nats-core, improving type narrowing for protocol parsing and JWT auth handling, and tightening type correctness in tests and tooling.

Changes:

• Update protocol message handling to use isinstance-based narrowing (Info/Err) instead of op checks.
• Adjust client callback and handler typing (notably error callbacks and _handle_info), plus refine JWT auth type narrowing.
• Fix minor typing issues in tests/bench tool and expand CI type-check coverage to include nats-core.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
nats-core/tools/bench.py	Removes an unnecessary type: ignore for sub.messages iteration.
nats-core/tests/test_protocol.py	Uses isinstance(msg, Err) for safer type narrowing in protocol parsing tests.
nats-core/tests/test_examples.py	Adds assertions/guard rails to satisfy typing and ensure CompletedProcess is always returned or an error is raised.
nats-core/tests/test_client.py	Adds a narrowing assertion for msg.reply in JWT request/reply test.
nats-core/src/nats/client/__init__.py	Improves protocol union narrowing, broadens error callback type, updates _handle_info typing, and refines JWT auth narrowing/validation.
.github/workflows/check.yml	Runs ty type checking for both nats-core and nats-server.

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[Copilot]

In _setup_jwt_auth, the elif isinstance(jwt, tuple) and isinstance(jwt[0], Path): branch does not verify that jwt[1] is also a Path, so the code needs a type: ignore and can still blow up at runtime if the tuple shape is wrong. Consider checking tuple length and isinstance(jwt[1], Path) in the condition and then assign without type: ignore.

[Copilot]

In the tuple-of-strings JWT branch, indexing (jwt[0], jwt[1]) plus assert isinstance(...) is weaker than the previous unpacking: it won’t validate tuple length (can raise IndexError) and assert can be stripped with python -O, removing the runtime type checks. Prefer explicit validation (e.g., length/type checks that raise TypeError) and/or unpacking to keep errors deterministic and user-friendly.

Suggested change

	jwt_str, seed_str = jwt[0], jwt[1]
	assert isinstance(jwt_str, str)
	assert isinstance(seed_str, str)
	if len(jwt) != 2:
	msg = f"jwt tuple must contain exactly 2 elements (jwt, seed), got {len(jwt)}"
	raise TypeError(msg)
	jwt_str, seed_str = jwt
	if not isinstance(jwt_str, str) or not isinstance(seed_str, str):
	msg = (
	"jwt tuple elements must be strings: "
	f"got types ({type(jwt_str).__name__}, {type(seed_str).__name__})"
	)
	raise TypeError(msg)