#468 Stale extension bundles break after swamp upgrade

After upgrading swamp (e.g. 20260523 → 20260527), pulled extension bundles in .swamp/bundles/ can become stale and fail to load with errors like:

error: Import "zod" not a dependency
    at file:///.swamp/pulled-extensions/@swamp/ssh/models/_lib/schemas.ts:27:22
error: bundling failed

The model silently disappears (Model not found: ssh) until the user manually deletes the stale bundle directory and re-pulls:

rm -rf .swamp/bundles/<hash>/
swamp extension pull @swamp/ssh --force

Expected: swamp update or the upgrade process should invalidate/rebuild stale bundles automatically. The swamp doctor extensions --repair command exists but doesn't catch this case since the bundle file physically exists — it's just compiled against an older bundler/runtime.

Environment: macOS, swamp 20260527.235818.0, extension @swamp/ssh 2026.05.25.1