Add story 51: Deterministic Spike Lifecycle Management

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.story_kit/stories/upcoming/51_deterministic_spike_lifecycle_management.md

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+---
+name: Deterministic Spike Lifecycle Management
+test_plan: pending
+---
+
+# Story 51: Deterministic Spike Lifecycle Management
+
+## User Story
+
+As a developer running autonomous agents, I want all spike file mutations to happen through server MCP/REST tools that auto-commit to master, so that spikes are tracked consistently alongside stories and bugs.
+
+## Prerequisites
+
+- Story 49 (Deterministic Bug Lifecycle Management)
+- Story 50 (Unified Current Work Directory)
+
+## Acceptance Criteria
+
+- [ ] New MCP tool `create_spike(name, description, goals)` creates a spike file in `.story_kit/spikes/` with a deterministic filename and auto-commits to master
+- [ ] New MCP tool `list_spikes()` returns all open spikes (files in `.story_kit/spikes/` excluding `archive/`)
+- [ ] New MCP tool `archive_spike(spike_id)` moves a spike from `.story_kit/spikes/` to `.story_kit/spikes/archive/` and auto-commits to master
+- [ ] `start_agent` moves spike files into `.story_kit/current/` and auto-commits
+- [ ] All auto-commits use deterministic commit messages (e.g. "story-kit: create spike spike-3-explore-foo", "story-kit: archive spike spike-3")
+- [ ] Agents never need to edit spike markdown files directly — all mutations go through server tools
+
+## Out of Scope
+
+- Spike-to-story conversion tooling
+- Time-boxing or expiry for spikes