From f23e2b2de0844887a46bdcae704205ebc8895a22 Mon Sep 17 00:00:00 2001
From: robbond <rob@rdbsolutions.co.uk>
Date: Wed, 12 Aug 2026 10:41:31 +0100
Subject: [PATCH] docs: record update-only previous-question fix

---
 docs/current-handoff.md  |  6 +++++
 docs/experiment-57j81.md | 51 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 57 insertions(+)
 create mode 100644 docs/experiment-57j81.md

diff --git a/docs/current-handoff.md b/docs/current-handoff.md
index 8de626e..41a27a4 100644
--- a/docs/current-handoff.md
+++ b/docs/current-handoff.md
@@ -183,6 +183,12 @@ _Created by Experiment 34. Updated by Experiments 38–53, 54A–54Z, 55A–55F,
 
 ---
 
+### Experiment 57J.81 — Update-Only Previous Question Fix
+
+**Objective:** Fix the 57J.80 apparatus defect where `FIXTURE_MODE=updateOnly` passes `previousQuestion = null` through to the production Zod validator, which rejects with `"Expected string, received null"` at `request_validation` stage before any model inference.
+
+**Classification: A — FIX VALIDATED (tooling only).** The pre-anchored fixture already contains the exact question text at `unresolved_question` ("Are the projected office savings from relocation realistic?"). Changed the harness to derive `previousQuestion` from that committed anchor (`fixtureData.unresolved_question ?? savingsNode.label`) instead of sending `null`. Source is the fixture anchor — no independent duplicate hardcoded question added. Zero production code changed. 49 harness tests pass (5 new deterministic regressions). The update-only apparatus can now reach the real production Update path without requiring Start.
+
 ---
 
 ### Experiment 57J.53 — Structured Fidelity Multi-Turn Progress
diff --git a/docs/experiment-57j81.md b/docs/experiment-57j81.md
new file mode 100644
index 0000000..e71fee9
--- /dev/null
+++ b/docs/experiment-57j81.md
@@ -0,0 +1,51 @@
+# Experiment 57J.81 — Update-Only Previous Question Fix
+
+**Branch:** `feature/semantic-action-contract-v0.23`
+**Starting HEAD:** `ce01e70` (tooling: add pre-anchored update-only mode to canonical harness)
+
+## Objective
+
+Fix the 57J.80 defect: update-only mode sends `previousQuestion = null`, which the production Zod validator rejects with `"Expected string, received null"` at `request_validation` stage, blocking all model inference.
+
+## Defect Source
+
+When `FIXTURE_MODE=updateOnly`, the harness sets `selectedQuestion = null` (line 242 of `reproduce-multi-turn-investigation.mjs`) and then passes it as `previousQuestion` to the Update request. The production validation schema (`lib/graph/schema.js:207`) requires `previousQuestion: z.string().min(1)`.
+
+## Fix
+
+**Source of previousQuestion:** FIXTURE ANCHOR (derived from committed fixture, not a hardcoded duplicate).
+
+The pre-anchored fixture already contains the exact question text in two locations:
+- `unresolved_question` at the fixture level (snake_case, from JSON)
+- The anchor node's `label` field on `n_savings_realism`
+
+**Change in harness** (`scripts/reproduce-multi-turn-investigation.mjs`):
+```javascript
+let selectedQuestion = fixtureData.unresolved_question ?? savingsNode.label;
+```
+
+This replaces `let selectedQuestion = null;` — both the harness and its test simulation now derive `previousQuestion` from the committed savings-realism anchor.
+
+**Exact previousQuestion:** `"Are the projected office savings from relocation realistic?"`
+
+## Classification: A — FIX VALIDATED (tooling only)
+
+One tooling commit fixes the boundary condition. The pre-anchored fixture already contains the required question string; no production code, prompts, or schemas changed.
+
+## Tests added
+
+1. Direct assertion that `previousQuestion` is a non-empty string
+2. Direct assertion that `previousQuestion` matches the committed savings-realism anchor exactly
+3. Direct assertion of exact fixture graph transmission (replaces indirect node-count check)
+4. Direct assertion of exact ANSWER_2 in request body
+5. Explicit zero-HTTP-call guard for missing ANSWER_2
+
+All 49 harness tests pass. Zero Ollama calls. Zero live API calls.
+
+## What this enables
+
+The update-only apparatus can now reach the production Update path without requiring a prior Start call. Experiment 57J.80's incremental-meaning test case is unblocked and ready to run against the model inference stage.
+
+## Production code changed: NO
+## Ollama calls: 0
+## Live API calls: 0