[FEATURE]: Conformance Tests for Rust/Go/Python plugin frameworks. #22

Epic: CPEX Rust Core (#12)

Summary

Create a shared test corpus of YAML scenario files that validate behavioral parity between the Python PluginManager and the Rust core. Scenarios are the source of truth for what "correct CPEX behavior" means.

Motivation

Multiple runtimes (Python, Rust, Go via FFI) must produce identical results for the same plugin configuration and input. Without a shared conformance suite, behavioral drift between runtimes is inevitable. The test corpus catches differences early and serves as the behavioral specification.

Scope

• YAML scenario format: hook type, plugin declarations (mode, priority, config), input payload, expected outcome (allow/deny/modify), expected extension state
• Scenario categories:
  • Hook ordering — plugins execute in priority order within each mode
  • 5-phase execution — sequential before transform before audit before concurrent before background
  • Allow/deny behavior — first deny halts pipeline, audit/transform can't block
  • Payload modification — modified payloads propagate to next plugin in chain
  • Extension modification — labels append-only, delegation chain append-only, custom mutable
  • Capability filtering — plugins only see declared extensions
  • Timeout semantics — plugin exceeds timeout, on_error behavior applies
  • Error handling — Fail/Ignore/Disable modes
• Test runner for Python: pytest loading scenarios from YAML
• Test runner for Rust: cargo test loading same YAML files
• Test runner for Go: go test loading same YAML files (when Go bindings available)

Acceptance Criteria

• At least 30 scenarios covering all categories above
• Python runner passes all scenarios against the existing Python PluginManager
• Rust runner passes all scenarios against cpex-core
• A scenario failure clearly reports: expected vs actual, which runtime, which scenario
• Adding a new scenario is just adding a YAML file — no code changes needed