confidence-engine/docs/experiment-57j78.md

Experiment 57J.78 — Pre-Anchored Update-Only Mode (Committed)

Branch: feature/semantic-action-contract-v0.23 Starting HEAD: 9b7721c (experiment: audit pre-anchored live apparatus) Commit message: tooling: add pre-anchored update-only mode to canonical harness

Objective

Eliminate the dependency on temporary uncommitted script modifications identified in audit 57J.77, by adding a committed pre-anchored update-only mode to the canonical harness (scripts/reproduce-multi-turn-investigation.mjs). This allows any agent session at current HEAD to inject an arbitrary graph into the Update request body without first running Start.

Changes Made

1. scripts/reproduce-multi-turn-investigation.mjs (+177 lines)

Added:

• ESM imports (fs, fileURLToPath, path) for deterministic fixture loading
• FIXTURE_PATH constant pointing to tests/fixtures/pre-anchored-update-savings-realism.json
• fixtureMode env-var selector (default: undefined → normal mode)
• runUpdateOnlyMode() async function:
  • Validates ANSWER_2 env-var exists before any live call
  • Loads committed fixture from deterministic path
  • Verifies single savings-realism anchor invariant
  • Deep-copies fixture graph (no mutation of original)
  • Skips Start entirely; sends exactly one Update via postJson() through production HTTP route
  • Preserves all hardened capture fields (answerMeaning, updatedProposal, structuralActionRequired, selectedQuestion, persistent graph snapshot)
  • Blocks on missing ANSWER_2 with zero live calls
  • Reports rejection diagnostics identically to normal mode

2. tests/reproduce-multi-turn-investigation.harness.test.js (+183 lines)

Added 7 new harness tests:

• Blocked ANSWER_2 → zero calls, correct error message
• Accepted structuralActionRequired=true in capture
• Rejected snapshot preservation with structural linkage errors
• Exact ANSWER_2 body forwarding verification
• Pre-anchored rejected answerMeaning preservation
• Blocked mode verification (zero fixture load errors)
• Normal-mode isolation proof (accepted/rejected capture unchanged)

Updated runPreAnchoredSimulation mock to persist rejectedProposalSnapshot on rejection return values. Added runPreAnchoredSimulationWithBlock() helper.

Evidence

Test Suite	Pre-existing	New	Total	Result
Harness harness tests	39	7	46	ALL PASS (19ms)

• No production code changed
• No Ollama calls made
• No live API calls made
• Normal-mode Start→Update chain preserved under guard
• Syntax validated via node --check

Execution Commands

Pre-anchored update-only mode:

FIXTURE_MODE=updateOnly \
  ANSWER_2="I am unsure whether the projected office savings from the relocation are realistic." \
  node scripts/reproduce-multi-turn-investigation.mjs

Normal start→update mode (unchanged):

node scripts/reproduce-multi-turn-investigation.mjs

Design Decisions

1. Environment variable over CLI flag: FIXTURE_MODE env-var is simplest, requires no arg parsing, and matches existing pattern (CONFIDENCE_ENGINE_BASE_URL).

2. ANSWER_2 required guard: Prevents accidental live calls without a clear answer payload. Zero calls made if missing.

3. ESM imports for path resolution: fileURLToPath(import.meta.url) resolves the fixture path relative to the script location, matching Node.js ESM best practices.

4. No schema/schema validator changes: The committed fixture file was already validated per existing schema enums in test 57J.74 (tests on lines 582-624 of the test file).

5. Normal mode guard: fixtureMode !== undefined check prevents the pre-anchored path from being activated when no env-var is set, preserving all existing start→update behavior.

Verification

1. All 46 harness tests pass in under 20ms
2. No production code was modified
3. Syntax validated via node --check
4. Normal-mode Start→Update chain preserved at its original location (line 63 of the mjs file)
5. Pre-anchored mode explicitly documented with inline JSDoc comments

Satisfies 57J.77 Recommendation

"Add committed pre-anchored mode to the canonical harness by adding a single config flag that bypasses Start and reads the fixture into the Update request body, mirroring what runPreAnchoredSimulation() documents as its intended behaviour."

This commit implements exactly that recommendation — runUpdateOnlyMode() is the committed implementation of what runPreAnchoredSimulation() previously documented only as a test-only mock.