3.9.0: ModelError exception note and relation data fixes

This release makes ModelError easier to diagnose, tightens how relation data permissions are enforced, and fixes a set of typing and ops.testing issues. There is also a new how-to guide on securing a charm.

New and improved

• ModelError now tells you which hook command failed, and during which event (#2786). When a call to Juju fails, a traceback notes line now shows what was running, so you no longer have to work it out the long full traceback chain.

Traceback (most recent call last):
  ...
ops.model.SecretNotFoundError: db-password
Hook command 'secret-get' (label='db-password', refresh=False, peek=False) failed during the 'config-changed' hook.

Fixes worth knowing about

• A relation that no longer exists raises RelationNotFoundError (#2748). Before this fix, it raised a ModelError with "permission denied" text.
• Tracing errors say which destination rejected the data (#2714). This helps when you send traces to more than one destination.
• Set on in charms and libraries without # type: ignore (#2775). Remove any type: ignore comments you added to get past the type checker.

In ops.testing

• If your charm's __init__ ends with _Abort(0) (such as a load_config() status set), the test treats it as a success (#2780). Before this fix, _Abort(0) counted as a success only when it came from an event handler.

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What's Changed

Features

• Add an exception note when ModelError is raised (#2786)

Fixes

• Make _CharmSpec covariant in its charm type (#2715)
• Say which tracing destination rejected the data (#2714)
• Detect Pydantic dataclasses from before 2.11 when mapping aliases (#2768)
• Enforce relation databag read permissions on all access paths (#2738)
• Use cached leadership in security logging, renew lease on success by @cristiangirlea (#2778)
• A gone relation raises RelationNotFoundError, not "permission denied" (#2748)
• Treat an _Abort(0) from the charm's __init__ as success in ops.testing (#2780)
• Record trace data in every ops.testing run with opentelemetry-sdk 1.45 (#2787)
• Let charms and libraries set on without a type: ignore (#2775)

Documentation

• Surface the tool versions page (#2712)
• Update Concierge links and intersphinx URLs in doc source (#2725)
• Add retry loop to version check in K8s tutorial charm (#2689)
• Merge HACKING.md into CONTRIBUTING.md, fewer files in root (#2734)
• Add a how-to guide for securing a charm (#2721)
• Condense and trim CONTRIBUTING.md (#2754)
• Fix the self-review command in the discoverability how-to (#2764)
• Mount the project directory to a target relative to the home directory (#2765)
• Pull tutorial code snippets from examples/ (#2544)

Tests

• Add conformance tests for the tracing and certificate_transfer interfaces (#2711)
• Make pyright check whole trees rather than a list of directories (#2779)

Refactoring

• Drop typing.cast where narrowing can do the work (#2723)
• Only import pdb when a debugger is actually requested (#2740)

CI

• Enrich scheduled-failure issues with an LLM triage pass (#2663, #2781)
• Stop tox writing a .venv redirect file in the examples (#2769)
• Move the release process from release.py to workflows (#2772)

Full Changelog: 3.8.2...3.9.0

Thanks @cristiangirlea for your contribution to this release!