# 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:

```text
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:

```text
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:

```text
Whether...
Uncertainty about whether...
Uncertainty regarding whether...
```

but not:

```text
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:

```text
unknown
uncertain
```

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

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

Each now exposes:

```text
whether X
```

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

## Focused Regression Behaviour

The exact 60B.27 regression now formulates:

```text
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:

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

Result:

```text
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.