# RetrieX Measurement Evidence Guard Fix

This patch tightens technical product-selection answers for measurement-parameter questions.

## Problem

The LLM could still merge similar water-treatment terms, for example treating `p-Wert` as `pH-Wert`, and then generate unsupported measurement ranges, application areas or recommendations.

## Change

The patch adds a generated `MEASUREMENT PARAMETER EVIDENCE CHECK` block to the final prompt when the user asks for configured measurement parameters such as pH, Redox/ORP or free chlorine.

For each relevant question, the PromptBuilder now:

- detects the requested measurement parameter from configurable YAML terms,
- scans RAG/URL context and each shop product record for explicit positive evidence,
- marks every shop record with a same-record evidence line,
- tells the model not to recommend a product when no explicit evidence exists,
- explicitly treats similar but non-equivalent terms such as `p-Wert`, `m-Wert`, `minus m-Wert`, `mmol/l` and alkalinity as insufficient for pH suitability.

## Files changed

- `src/Agent/PromptBuilder.php`
- `src/Config/PromptBuilderConfig.php`
- `config/retriex/prompt.yaml`

## Intended behavior

For `suche einen testomat der ph messen kann`, if the provided RAG/shop records only contain `p-Wert` or related alkalinity values but no explicit `pH` / `pH-Wert` evidence in the same record, the answer should start with uncertainty, for example:

`Ich finde in den bereitgestellten Quellen keinen sicher belegten Testomat fuer pH-Messung.`

It may still list shop hits as commercial/search hits, but not as verified pH-suitable devices.

## Scope

This patch does not touch retrieval, scoring, shop search, AgentRunner, SSE or LLM settings.
