docs: record uncertainty identity clarification

docs/current-handoff.md

@@ -1029,3 +1029,15 @@ One fresh live run through the production `startCase()` → `updateCase()` path.
 **What this establishes:** v0.20's structured semantic fidelity path executes live on the real production path. The model populates structured fields from a "I am unsure..." answer, the validator trusts those populated fields over lexical comparison, and meaningful graph structure is produced.
 
 **What this does NOT prove:** Stability across repeated runs; behavior for answers outside existing categories; `must_remain_unresolved` enforcement in practice; end-to-end investigation viability past Update 2+. Full record in `docs/experiment-57j52.md`.
+
+### Experiment 57J.55 — Uncertainty Identity Clarification (Prompt-Only)
+
+**Objective:** Implement the correction from Experiment 57J.54: clarify that "same uncertainty" means the same resolution question, not topical overlap. Bounded prompt-only task — no schema, validator, graph-model, or provider changes.
+
+**Changes:**
+- `lib/graph/prompt-builder.js`: Added to Additional Guidance — *"Same uncertainty means the same resolution question: resolving the existing unknown would also resolve the uncertainty introduced by the user's answer. Mere topical overlap (concerning the same topic, object, decision, or domain) is not automatically the same uncertainty."*
+- `tests/graph/prompt-builder.test.js`: 10 new focused prompt tests verifying the definition, boundaries, and preserved contracts (49 total pass).
+
+**Test results:** All 49 tests pass. No regression in existing prompt structure tests.
+
+**Configured Ollama:** none used. **Production code changed:** NO. **Ollama calls:** 0.