Merge: origin's sync ordering and adoption work, its scan-complete trigger ported into library_ui/

docs/dev/requirements.md

@@ -1814,6 +1814,28 @@ tool for a hand-held set, and a photograph with real parallax is not a panorama.
 in one operation until HDR merge exists on its own. No live re-stitch: a different projection or
 crop after the fact is a new file, not an edit. No video.
 
+### 3.12 Inference runtime
+
+The face, segmentation and border-fill models run under an inference engine the application
+selects per device. [inference.md](inference.md) is the design: its §3 sets the dependency policy
+the runtime may reopen, its §10 the milestones (M1–M7) the clauses below cite as acceptance. The
+clauses are the register entries inference.md §12 promised; they are stated here so the
+traceability gate can count them.
+
+**FR-INF-1 — Runtime selection.** On launch the application shall determine, per device and
+without blocking the first frame, the fastest inference backend that can build and run a session
+for the shipped models, by attempting it; shall record and reuse that determination until the
+runtime, driver, hardware or models change; and shall display the backend in use in Settings and
+on the about screen. *Acceptance:* inference.md §10 M1 and M5.
+
+**FR-INF-2 — Derived engines.** Backends that require device-specific compilation shall compile in
+the background after selection, shall serve requests from the next lower backend until each engine
+is ready, and shall not change the backend of a job in progress. *Acceptance:* M5.
+
+**FR-INF-3 — Model forms.** Quantised model forms are produced at release time from real
+calibration data and are shipped only when they meet inference.md §10's accuracy gates against the
+canonical form; the application never quantises on the device. *Acceptance:* M2, M7.
+
 ---
 
 ## 4. Non-functional requirements
@@ -2111,6 +2133,13 @@ it is far cheaper to discover now than after the UI is built.
 clipping indicators (FR-DSP-7), and the HSL mixer carry a shape or text affordance. This matters
 more in a colour-grading application than in most software.
 
+### 4.10 Inference
+
+**NFR-INF-1 — Embedding comparability.** Face embeddings shall be computed at a precision whose
+deviation from the f32 reference is within [inference.md](inference.md) §7's gate, on every
+backend, so that embeddings from any device are comparable — FR-CULL-9's calibration depends on
+it. *Acceptance:* inference.md §10 M3.
+
 ---
 
 ## 5. Data model and architecture