docs: add independent timing holdout protocol

docs/research/day_level_holdout_v3_annotation_protocol.md

@@ -0,0 +1,55 @@
+# Day-Level Holdout V3 Annotation Protocol
+
+Purpose: collect independent, source-backed timing labels for
+`references/real_case_calibration/day_level_holdout_v3_preregistration.json`.
+This packet does not alter chart rules, thresholds, or product wording.
+
+## Independence
+
+- The annotator must not have edited timing rules or existing control dates.
+- `adjudicator` identifies the independent person or organization that resolved
+  ambiguity. It must not be the timing-rule author.
+- Use a public source URL for every row. Do not use an absent search result as
+  evidence of `no_target_event`.
+
+## One annotation row
+
+```json
+{
+  "case_id": "public_subject_stable_id",
+  "domain": "career",
+  "label": "target_event",
+  "start": "YYYY-MM-DD",
+  "end": "YYYY-MM-DD",
+  "source_url": "https://public-source.example/event",
+  "adjudicator": "independent-labeler-id",
+  "time_uncertainty_days": 0
+}
+```
+
+`label` is exactly one of:
+
+- `target_event`: source establishes the requested event in the stated interval.
+- `no_target_event`: source establishes a genuine non-event interval, such as a
+  dated diary, schedule, or contemporaneous record that would have recorded the
+  target event. Mere silence is invalid.
+
+Use day precision only when the source supports it. Otherwise widen `start` and
+`end`, and record the uncertainty in `time_uncertainty_days`.
+
+## Frozen acceptance gate
+
+- At least 20 independently labeled positive cases.
+- At least 80 independently labeled negative intervals.
+- Every row has all eight fields shown above and a public URL.
+- Existing four-control and pilot files remain prohibited from tuning.
+
+Before submitting labels, run:
+
+```bash
+python3 scripts/day_level_holdout_validator.py \
+  references/real_case_calibration/day_level_holdout_v3_preregistration.json
+```
+
+Only `ready_for_blind_replay` permits a blind replay. It still does not permit
+retuning the frozen rules.

references/real_case_calibration/day_level_holdout_v3_preregistration.json

@@ -3,6 +3,7 @@
   "status": "awaiting_independent_labels",
   "frozen_rule_version": "v3_preregistered_not_tuned",
   "truth_policy": "independent_source_and_adjudicator_required",
+  "annotation_protocol": "docs/research/day_level_holdout_v3_annotation_protocol.md",
   "prohibited_tuning_data": [
     "docs/benchmark/public_real_case_negative_controls_holdout_v2_4controls_20260717.json",
     "docs/benchmark/public_real_case_negative_control_pilot_2026_07_11.json"