ADR-002: Plugin contract versioning

Status: ACCEPTED
Date: 2026-05-08
Deciders: cproudlock
Supersedes: none

Context

Once sister sites start writing their own plugins (or pulling community plugins), the framework's plugin contract becomes a public API. Without a versioning story, any change to BasePlugin or the core platform models can silently break installed plugins at remote sites.

The existing BasePlugin and PluginMeta already declare a core_version field (default ">=1.0.0"), but it is not enforced anywhere. The plugin loader does not check it before instantiation.

Decision

The framework adopts semantic versioning for the plugin contract, declared in two places:

Framework version (shopdb/__init__.py): a single __contract_version__ constant. This is the version of the platform contract as defined in ADR-001. Bumped according to semver:
- Major: breaking change to BasePlugin ABC, PluginMeta schema, or any model in the platform contract (Asset, AssetType, AssetStatus, AssetRelationship, Vendor, Location, BusinessUnit, Model, OperatingSystem).
- Minor: additive change (new optional hook, new field on a contract model with default).
- Patch: bug fix, no contract surface change.
Plugin requirement (plugins/<name>/manifest.json): the existing core_version field, expressed as a semver range (e.g., ">=1.0.0,<2.0.0").

The plugin loader (shopdb/plugins/loader.py) checks core_version against __contract_version__ at load time. Mismatch in dev = re-raise (fail loud). Mismatch in prod = log error, mark plugin as incompatible, exclude from registration.

The __contract_version__ starts at 1.0.0 when ADR-001 is accepted and the Machine retirement migration is complete (whichever comes later). Until then, the framework is pre-1.0; plugins should declare core_version: ">=0.1.0,<1.0.0".

Consequences

Positive

Sister sites can pin a known-good framework version. They will not be silently broken when the framework is upgraded.
Plugin authors know what counts as a breaking change because the contract surface is enumerated in ADR-001.
The loader fails predictably: a mismatched plugin is reported, not silently disabled.

Negative / cost

Discipline required: every change to the contract surface must be classified (major / minor / patch). Adding a version-bump skill (or a check in code review) reduces the chance of mis-classification.
__contract_version__ becomes a coupling point. Forgetting to bump it after a breaking change means downstream plugins crash silently at runtime instead of failing at install.

Neutral

Existing plugins (plugins/printers/, etc.) ship as part of the framework, so their core_version is always the current __contract_version__. The discipline matters mostly for external / sister-site plugins.

Alternatives considered

No versioning, just trust. Works for an in-tree-only world. Fails the moment a sister site ships its own plugin. Rejected.
Calendar versioning (e.g., 2026.05.0). Easier to bump, harder to communicate breaking changes. Rejected; semver is the industry standard for library-like contracts.
Per-hook versioning. Each hook has its own version. Too granular; plugins still couple to multiple hooks. Rejected.

Open questions

When does the framework declare 1.0.0? Tied to ADR-001 (Asset retirement of Machine) and the framework being deemed "ready for sister sites". Best-effort target: end of Phase 5 in the refactor plan.
Should core_version accept commercial-grade ranges (^1.0.0) or stick to PEP 440 / npm-style ranges? Recommend pip-style (>=,<) to match Python ecosystem.

References

shopdb/plugins/base.py (PluginMeta declaration)
shopdb/plugins/loader.py (where the version check belongs)
ADR-001 (defines what is in the contract)

Docs

Install and operate

Data import

Plugins

Integrations

Project

ROADMAP

ADRs

Proposals

PROPOSAL-ge-enforce-plugin