confidence-engine/docs/experiment-60b28.md

Experiment 60B.28 — Explicit Uncertainty Prefix Proposition Coverage

Branch: feature/proposition-prefix-coverage-v0.31
Starting HEAD: 4e66e1ffbf1b8aa9103f72430c14e26d48f7f1fd
Date: 2026-08-14
Status: COMPLETE

Objective

Close the narrow live coverage gap identified in 60B.27 by extending bounded proposition-prefix normalisation so explicit uncertainty forms beginning:

Unknown whether...
Uncertain whether...

enter the same whether ... proposition-extraction path already established in 60B.26.

60B.27 Coverage Gap

60B.27 confirmed that the live cleanup from 60B.26 was working correctly for:

• material target preservation
• evidence framing activation
• explanatory rationale removal from the final question
• source graph meaning preservation

But the live node description began:

Unknown whether one prospective enterprise customer will sign if we launch this year, so that the remaining £700k of the expected £1.2M annual revenue is realized.

The existing bounded proposition path recognised:

Whether...
Uncertainty about whether...
Uncertainty regarding whether...

but not:

Unknown whether...
Uncertain whether...

So formulation fell back to the nominal label instead of preserving the full unresolved proposition.

Exact Prefix Normalisation Added

Production change was limited to lib/graph/question-formulator.js.

Inside extractMeaning(), the description-start normalisation used before the existing ^whether proposition check now also strips these explicit uncertainty prefixes case-insensitively:

unknown
uncertain

This means the following bounded forms are now treated equivalently for proposition extraction:

Whether X...
Unknown whether X...
Uncertain whether X...
Uncertainty about whether X...
Uncertainty regarding whether X...

Each now exposes:

whether X

before the existing rationale-boundary stripping and evidence framing logic runs.

Focused Regression Behaviour

The exact 60B.27 regression now formulates:

What evidence would clarify whether one prospective enterprise customer will sign if we launch this year?

The final question excludes:

• £700k
• £1.2M
• annual revenue

while the source node description remains unchanged.

Additional focused deterministic coverage also confirms:

• Uncertain whether... preserves the proposition with evidence framing
• bare Whether... remains unchanged
• Uncertainty about whether... remains unchanged
• Uncertainty regarding whether... remains unchanged
• direct interrogatives remain unchanged
• nominal non-whether behaviour remains unchanged
• formulation-only cleanup does not mutate the source description

Preserved Existing Paths

This change did not:

• redesign question formulation
• broaden parsing beyond explicit uncertainty markers
• convert arbitrary unknown descriptions into propositions
• mutate graph descriptions
• change question templates, routing, provider logic, schema, or proposal application

Verification

Focused command run exactly as bounded:

npx vitest run tests/graph/question-formulator.test.js

Result:

PASS — 37/37 tests

What Remains Unproven Until Exact Live 60B.27 Rerun

Deterministic formulation coverage is now proven for the targeted prefix gap, but the exact live end-to-end 60B.27 rerun is still required to reconfirm that the same proposition-preserving output appears through the full runtime path with live model-selected graph updates.