# BrepFaultProbe Lessons

This file records the failure patterns that have already appeared in this project.

## 1. Do not require explicit labels when the geometry can be inferred

The sleeve-removal `b` case failed at first because the judge only accepted edges explicitly tagged as `push_face`.

Correct rule:

- accept explicit labels when present
- also infer the same feature from B-rep structure
- treat explicit labels as strong evidence, not the only evidence

## 2. Keep candidates separate from decisions

`*_candidate` is evidence, not a final answer.

If the pipeline mixes candidate evidence with final template matching, the judge will drift into false negatives or false positives.

## 3. Outer frame is not a functional feature

For 2D sketch graphs, the outer frame can be a valid drawable loop, but it does not by itself mean the image contains a meaningful machine-design feature.

Always separate:

- background outer frame
- actual functional loops
- inferred feature loops such as holes, slots, bosses, and ports

## 4. Image and model must share a canonical middle form

Raw raster edges and true section edges are not directly comparable.

The stable comparison point is:

- vertices
- drawable edges
- paths
- loops
- regions
- relations
- dimensions

## 5. Hatch lines are annotations

Section hatches must be excluded from drawable contour edges.

If they are treated as normal edges, the sketch graph becomes noisy and the loop/path matcher starts inventing structure.

## 6. One sample is not enough

A rule that works on one positive case may still fail on:

- unrelated cases
- weak candidates
- cases with no explicit role tags
- cases whose functional feature is expressed by a different geometric cue

Always verify at least:

- a positive case
- a negative case
- an unrelated case
- a weak/noisy case

## 7. Current open risk

`b` has been upgraded to infer push-face evidence from B-rep topology.

`c` and `d` still depend more on explicit region semantics, so they can repeat the same failure mode if the upstream extractor does not label them clearly enough.

## 8. Textbook image rules must name the exact measurable geometry

Failure pattern:

- A textbook rule says a "diameter" should be larger, but the drawing contains many diameters.
- If the extracted knowledge only says `boss_diameter > cover_diameter`, the B-rep pipeline may measure the wrong diameter, such as an inner hole, register-fit diameter, bearing-seat bore, bolt hole, or bolt-circle diameter.

Correct rule:

- The knowledge chunk must explicitly define the compared geometry by position and boundary role.
- Use terms such as `mounting-side outer contour`, `maximum outer diameter`, `cast boss outer boundary`, and `minimum boundary margin`.
- Also list excluded diameters when they are plausible distractors.

For Chapter 18.2.1, the rule is:

- compare the end cover mounting-side flange outer boundary or maximum outer diameter
- against the cast housing boss/recess/allowance-region outer boundary or maximum outer diameter
- require the housing cast boss boundary to contain the cover flange boundary with casting-position-error allowance
- do not compare the cover inner hole, register-fit diameter, bearing-seat bore, bolt holes, or bolt-circle diameter

Every image-to-rule extraction should preserve this level of specificity so model-side B-rep facts can be selected without ambiguity.