Adapter security

Third-party adapters must not get unrestricted host access.

Permissions (`AdapterPermissions`)

Flag	Meaning
`read_project`	Read source tree
`write_output`	Write generated files
`execute_build`	Run build/test tools
`network`	Network I/O
`read_environment`	Read env vars

Built-ins use a fuller permission set. External adapters default to minimal (read_project only) once package loading lands.

Isolation goals

Crash isolation (ADAPTER_FAILURE without killing the migration)
Timeouts and memory budgets for untrusted adapters
Deterministic hooks only

Telemetry from plx adapters report is local-only by default.