docs: add crawler A/B experiment tracking (7 days)

Signed-off-by: Ikalus1988 <sheldonisspark@gmail.com>

Author: sheldonisspark-lab

docs/field-reports/crawler-ab-experiment-2026-07-14.md

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+# Crawler A/B Experiment — 2026-07-14
+
+## Hypothesis
+
+v2.8.0 had crawler PRs because issues had `bounty` label and standard bounty formatting. v2.9.0+ lost crawlers when labels changed to `zero-bounty` / `status:competition`.
+
+## Experiment Design
+
+**Start:** 2026-07-14
+**End:** 2026-07-21 (7 days)
+**Metric:** External PRs, issue comments, claims
+
+### Experimental Group (6 issues)
+
+Enhanced with: `bounty` label + `[Bounty][$0]` title prefix + reward text in body
+
+| Issue | Title | Type |
+|-------|-------|------|
+| #429 | [Bounty][$0][agent competition] Blind test homepage SAG-Lite search | Test |
+| #459 | [Bounty][$0][Benchmark] Run LessonReuseBench | Benchmark |
+| #290 | [Bounty][$0][Docs] 5-minute quickstart | Docs |
+| #302 | [Bounty][$0][Search] Show match reason | Search |
+| #304 | [Bounty][$0][Search] --json output | Search |
+| #257 | [Bounty][$0] Translate Chinese lessons | Content |
+
+### Control Group (remaining issues)
+
+Standard labels: `status:competition`, `agent-friendly`, no `bounty` label
+
+| Issue | Title | Type |
+|-------|-------|------|
+| #352 | Decide verified/ semantics | Protocol |
+| #354 | Add trust_tiers | Protocol |
+| #318 | Cursor integration | Ecosystem |
+| #317 | VS Code extension | Ecosystem |
+| #313 | Query expansion | Search |
+| #314 | Typo tolerance | Search |
+| ... | (others) | Various |
+
+## Baseline (pre-experiment)
+
+| Metric | Experimental | Control |
+|--------|-------------|---------|
+| External PRs | 0 | 0 |
+| Issue comments | 0 | 0 |
+| Claims | 0 | 0 |
+
+## Day 1 (2026-07-14)
+
+- Added `bounty` label to all 22 competition issues
+- Updated 6 experimental issues with `[Bounty][$0]` title + reward text
+- Waiting for crawler discovery
+
+## Day 7 (2026-07-21)
+
+(TODO: fill in results)
+
+| Metric | Experimental | Control |
+|--------|-------------|---------|
+| External PRs | | |
+| Issue comments | | |
+| Claims | | |
+| Unique contributors | | |
+
+## Conclusion
+
+(TODO: fill in after 7 days)