Record what the spec got wrong about the model that exists

docs/segmentation.md §4 priced arm B as costing a C dependency under the
NDK and treated that as most of the difference between the arms. It is not
a cost that has to be paid: `ort`'s `alternative-backend` disables its
linking entirely and `ort-tract` supplies the API from tract, which is pure
Rust. D13's "largest exception the policy would tolerate" turns out not to
be needed, and the answer generalises to the face pipeline — so D13's
runtime half is now answered and only its licensing half is open.

Three findings contradict §4 outright and are recorded as F4-F6 rather than
quietly designed around. There is no ADE20K-trained YOLO, so the shipped
vocabulary selects subjects and not stuff — "select the sky" comes from the
watershed or from nowhere. It is instance segmentation, so it partitions
nothing and two people come back as two instances. And tract cannot parse a
dynamic-shape export, which fixes the input at 640 square and makes tiling
the only route to more semantic resolution.

Arm C ships, but §8's criteria are not what decided it, and saying so
matters more than claiming the process worked. §8 asked for a two-
interaction margin over arm A on a traced corpus. That comparison was never
run: F4 and F5 changed what the arms are, and a model that recognises
subjects but has no word for sky cannot be a selection tool alone, while a
watershed cannot tell a person from the wall behind them. They stopped
being candidates and became complements.

What is *not* done is written down as plainly: the 24-image corpus is
untraced, so M1-M4 have no numbers and "this feels right" has not become
one. M5 is answered on one device only, and region ids now reach the
sidecar — so a cross-vendor divergence would mean a mask written on the
desktop meaning something else on Android. F3 stands.

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				@@ -1084,7 +1084,8 @@ Full rationale in [requirements.md §8](requirements.md). Summary:

				| D10 | Single adaptive interface | Decided |

				| D11 | Product positioning | Decided |

				| D12 | Scope versus pace | **Open** |

				| D13 | Face inference runtime and model licensing | **Open** |

				| D13 | Face inference runtime and model licensing | **Runtime answered**, licensing open |

				| D14 | Segmentation source for local masking | Decided — arm C (docs/segmentation.md §14) |

				---