feat(ffi): surface auth connect errors in language wrappers

[kixelated]

Follow-up to #1649, which added Unauthorized (HTTP 401) and Forbidden (HTTP 403) variants to the moq-ffi MoqError so callers can distinguish an auth rejection from a retryable transport failure. That PR landed the Rust side but left the language wrappers without an ergonomic way to act on the new variants (the Cross-Package Sync row for rs/moq-ffi). This closes that gap.

Summary

Parity helpers next to the existing isShutdown:

• Swift — MoqError.isAuth (true for .Unauthorized / .Forbidden)
• Kotlin — MoqException.isAuth
• Go — moq.IsAuthError(err), using errors.Is over the generated ErrMoqErrorUnauthorized / ErrMoqErrorForbidden sentinels
• Python — re-export MoqError from the moq package so callers can except moq.MoqError.Unauthorized without reaching into moq_ffi

Plus an auth-error note in each wrapper's guide (doc/lib/{swift,kt,go,py}) and the C library doc (doc/lib/c), which documents the distinct return codes + moq_error() strings since libmoq has no named C constants for them.

The variants themselves are already emitted by every binding (flat UniFFI error), so this is purely the ergonomic + documentation surface.

Test plan

• CI just ci runs just {py,kt,go} check on the Linux runner (these wrappers were skipped for fix(native): surface terminal auth connect errors #1649 since it didn't touch them); Go compiles IsAuthError against freshly-regenerated bindings that now include ErrMoqErrorForbidden.
• swift check is macOS-only and skips on the Linux runner; the isAuth helper mirrors the existing isShutdown exactly.
• gofmt clean; Python isort/__all__ ordering consistent with existing style.

(Written by Claude)

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 9c5f81ef-e71c-4052-920d-92c14409746b

📥 Commits

Reviewing files that changed from the base of the PR and between b7cd320 and 49640b2.

📒 Files selected for processing (9)

• doc/lib/c/index.md
• doc/lib/go/moq.md
• doc/lib/kt/moq.md
• doc/lib/py/moq-rs.md
• doc/lib/swift/moq.md
• go/moq/errors.go
• kt/moq/src/jvmAndAndroidMain/kotlin/dev/moq/Errors.kt
• py/moq-rs/moq/__init__.py
• swift/Sources/Moq/Errors.swift

✅ Files skipped from review due to trivial changes (5)

• doc/lib/kt/moq.md
• doc/lib/go/moq.md
• doc/lib/c/index.md
• doc/lib/swift/moq.md
• doc/lib/py/moq-rs.md

🚧 Files skipped from review as they are similar to previous changes (4)

• py/moq-rs/moq/init.py
• swift/Sources/Moq/Errors.swift
• go/moq/errors.go
• kt/moq/src/jvmAndAndroidMain/kotlin/dev/moq/Errors.kt

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Walkthrough

This PR adds authentication/authorization error handling guidance and helpers across the Moq SDK ecosystem. Implementations in Go, Kotlin, and Swift each provide an isAuth or IsAuthError convenience helper to detect HTTP 401/403 rejections, which are marked as terminal and non-retryable. Python's MoqError is exported in the public API to enable direct exception handling. All language bindings include documentation with code examples demonstrating how to distinguish authentication failures from transient transport errors, prompting for new credentials instead of reconnecting.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'feat(ffi): surface auth connect errors in language wrappers' accurately summarizes the main change—adding ergonomic helpers and documentation to expose authentication/authorization errors in language wrappers.
Description check	✅ Passed	The description clearly relates to the changeset, explaining the motivation (follow-up to #1649), the specific changes across all four language wrappers (Swift, Kotlin, Go, Python) and C documentation, and the test plan.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

✨ Simplify code

• Create PR with simplified code
• Commit simplified code in branch fix/wrapper-auth-errors

Warning

There were issues while running some tools. Please review the errors and either fix the tool's configuration or disable the tool if it's a critical failure.

🔧 golangci-lint (2.12.2)

level=error msg="[linters_context] typechecking error: pattern ./...: directory prefix . does not contain main module or its selected dependencies"

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[kixelated]

@Qizot do you need this?

[Qizot]

@kixelated yes, please