chore(agents): pin Python v0.0.50

[AntoineToussaint]

Production finding

Mind’s live Pytest rerun continued to launch python__0.0.48 after the fixed Python v0.0.50 release became globally resolvable. This is expected from the CLI’s reproducible source-workspace contract: the CLI pin, not latest-version discovery, is authoritative.

Change

Advance GenericPythonPluginVersion from v0.0.48 to the qualified v0.0.50 release containing Core v0.2.126 tox/nox test-command derivation.

Proof

• Python v0.0.50 release CI and three-platform GoReleaser green
• GOWORK=off go test ./pkg/sourceworkspace ./pkg/engine ./cmd/test -count=1
• GOWORK=off go vet ./pkg/sourceworkspace ./pkg/engine ./cmd/test
• complete GOWORK=off go test ./... -count=1
• complete GOWORK=off go vet ./...
• git diff --check

After the CLI release, the same Mind production cell will verify that the runtime actually launches python__0.0.50 and derives pytest rather than release automation.