pure plugin reconciler poc

this branch isolates the framework-free implementation from the three-way plugin runtime experiment.

shape

• an iterative capability graph plans activation and targeted restarts
• plugin instances own explicit lifo finalizer stacks
• contributions are staged per plugin and published as frozen snapshots
• failed candidates are cleaned up without replacing the live composition
• cleanup attempts every dependent-first instance and aggregates failures

this is the smallest and fastest planner in the experiment. for production, its graph algorithm should drive effect scopes rather than keeping manual finalizer ownership.

proved

• 32 tests cover dependency order, blocking, rollback, cycles, unchanged instance reuse, order-insensitive declarations, activation implementation replacement, active callback reentrancy, synchronous callback microtasks, plain-function callback returns, prompt activation-context expiry, descendant async tasks, late activation-context calls, queued input snapshots, observer isolation, cleanup reporting, unusual ids and slots, immutable snapshots, and a 20,000-plugin stack-safe chain
• manifest validation enforces semver, prevents entrypoint path escape, and keeps mobile declarative
• the demo exercises activation, replacement, teardown, and a 250-plugin chain

run

vp test run packages/plugin-runtime-poc/src
vp run --filter @t3tools/plugin-runtime-pure-poc typecheck
vp run --filter @t3tools/plugin-runtime-pure-poc demo

this is an isolated runtime poc. it does not load packages, add a sandbox, expose plugin rpc, or wire product ui.