Phase 2 (#1075): Migrate simple stages run(state) → run(gremlin)

[xbrianh]

Part of #1075. Depends on #1090 (Phase 1).

Stages

base.py, composite.py, sequence.py, exec.py, agent.py, agent_runner.py

What

1. Change StageProtocol abstract signature in base.py to run(self, gremlin: Gremlin) -> Outcome.
2. Change every concrete run(self, state: State) to run(self, gremlin: Gremlin).
3. Inside each body, replace every state.X with gremlin.state.X.
4. Drop from gremlins.executor.state import State from each file.

Callsite change in _collect_stages: state.make_runner(stage) → pass gremlin directly; make_runner assigns gremlin.state then calls await stage.run(gremlin).

Files

• gremlins/stages/base.py
• gremlins/stages/composite.py
• gremlins/stages/sequence.py
• gremlins/stages/exec.py
• gremlins/stages/agent.py
• gremlins/stages/agent_runner.py
• gremlins/executor/gremlin.py (make_runner update)

Tests

Suite passes. No behavioral change — gremlin.state.X forwards identically to the old state.X.