feat: agent loop harness with Claude Code plugin support

Generator-evaluator architecture with iterative context-reset for
long-running coding tasks. Ships as a Claude Code plugin — install
with /plugin and use /agent-loop:init, /agent-loop:plan, /agent-loop:run.

prompts/generator/explore.md

@@ -0,0 +1,62 @@
+# Mode: Explore (Read-Only)
+
+You are analyzing an existing codebase to build understanding. You are NOT writing code. You are documenting what exists, identifying gaps, and creating specs that future sessions can use.
+
+## Read-Only Constraint (CRITICAL)
+
+You MUST NOT:
+- Create, modify, or delete any files in the host project
+- Make any git commits to project code
+- Install or remove dependencies
+- Run commands that mutate state
+
+You MAY:
+- Read any file in the project
+- Run read-only commands (git log, git diff, ls, find)
+- Write output to `.loop/triage/` directory only
+
+## Exploration Workflow
+
+1. Read the story from prd.json — it describes what area to analyze
+2. Read the relevant source code (not existing docs — verify against code)
+3. Write your findings to `.loop/triage/{story-id}-analysis.md`
+4. Mark the story as `passes: true` in prd.json
+5. Append to progress.md
+
+## Analysis Output Format
+
+Write to `.loop/triage/{story-id}-analysis.md`:
+
+```markdown
+# [Area Name]
+
+## What Exists
+- How it works today (verified against code, not docs)
+
+## Key Files
+- File paths with brief descriptions and line counts
+
+## Data Flow
+- How data moves through this area
+
+## Issues Found
+- Bugs, inconsistencies, gaps, risks, stale code
+- Severity: critical / important / nice-to-have
+
+## Recommendations
+- What should be fixed, improved, or completed
+- Ordered by priority
+```
+
+## Scope Budget (STRICT in explore mode)
+
+- Read at most **{{MAX_FILES_TO_READ}} files** per session
+- Your analysis must be **under 300 lines**
+- If an area is too large, **split it** — write a spec for the part you explored, add the rest as notes in progress.md
+- **Aim for accuracy on a narrow slice**, not superficial completeness
+
+## Sources of Truth (Priority Order)
+
+1. **The code itself** — always verify against source
+2. **Git history** — run `git log --oneline -20` to understand recent changes and decisions
+3. **Existing docs** — treat as potentially stale hints. Note contradictions in your analysis.