story-kit: remove 66_spike_pipeline_stage_state_machine

.story_kit/work/1_upcoming/66_spike_pipeline_stage_state_machine.md

@@ -1,25 +0,0 @@
----
-name: Pipeline Stage State Machine Spike
-test_plan: pending
----
-
-# Story 66: Pipeline Stage State Machine Spike
-
-## User Story
-
-As a Story Kit developer, I want to explore a generalised pipeline stage pattern where each stage is defined by filesystem convention (config.toml, setup script, verify script) and the server drives a uniform loop: enter, validate, setup, execute agent, verify, gate, advance.
-
-## Acceptance Criteria
-
-- [ ] Document the proposed directory structure: .story_kit/pipeline/{stage}/config.toml|setup|verify
-- [ ] Document how work/ directories mirror pipeline/ definitions
-- [ ] Document config.toml schema: agent name, gate policy (advance vs hold)
-- [ ] Document how setup and verify scripts work (executables, exit 0 = pass, env vars passed in)
-- [ ] Document how custom stages would work (user-defined, no Rust changes needed)
-- [ ] Document how human-in-the-loop gates work at each stage (configurable auto-advance vs hold-for-approval)
-- [ ] Evaluate trade-offs vs current hardcoded stage approach
-- [ ] Recommend: implement as-is, simplify, or defer
-
-## Out of Scope
-
-- TBD