Record progressive refinement as built, and the fit view's two speed-ups

display-and-extension.md still called FR-DSP-4 absent, and
frame-budget.md ended its reading at "satisfied vacuously". 0.15.0 built
it (refine.rs, the provisional histogram, the fade), so the table row
says so, frame-budget.md gains a note under its FR-DSP-4 section, and the
register gains a status note like FR-RAW-2's and FR-UI-5's.

frame-budget.md also gains a short section with the figures 1dc7b45
(the fit view's gather cached per framing) and d430ec9 (an identity
detail pass dropped) measured, since its fit rows no longer describe the
fused path. They are quoted from those commits, on the machine they name,
and are marked as not re-run here.

docs/dev/display-and-extension.md

@@ -22,7 +22,7 @@ and the reason is that some of the work is done and untagged.
 | FR-DSP-1 proxy rendering | **Done.** The develop view renders at viewport resolution, not source. |
 | FR-DSP-2 tiled computation | **Absent, and §2 now says it should stay that way.** Measured: the fused pass is inside the budget everywhere. See [frame-budget.md](frame-budget.md). |
 | FR-DSP-3 interactive latency | **Measured and asserted** for the fused path — `core/dr-gpu/tests/frame_budget.rs`. Missed by one operation, clarity, for the reason recorded as TD-4. |
-| FR-DSP-4 progressive refinement | **Absent**, and §4's condition did not fire. Every render is full quality and can afford to be. |
+| FR-DSP-4 progressive refinement | **Built** (0.15.0), although §4's condition did not fire on the fused path: a half-resolution draft while a gesture moves, one sharp frame 120 ms after it stops, the histogram dimmed while it lags, and the draft faded out over 150 ms — `ui/dr-ui/src/refine.rs`. See [frame-budget.md](frame-budget.md). |
 | FR-DSP-5 zoom and pan | **Done and tagged**, against tests that fail if the behaviour is removed — `core/dr-gpu/tests/zoom_resolution.rs`. `Framing::view` shrinks the sampled region while the render target keeps its size, so zooming *raises* the resolution the pipeline works at. That is FR-DSP-5's requirement, arrived at without tiles. |
 | FR-DSP-6 colour management | **Done.** Output space is a parameter of composition. |
 | FR-DSP-7 histogram and clipping | **Done**, GPU-side, no per-frame readback. |

docs/dev/frame-budget.md

@@ -264,6 +264,14 @@ base, computed at reduced resolution and correct at any moment the user stops.
 "Render coarse while dragging, sharpen when it settles" would paper over the same
 34 ms with a visible swap. Fix the stage.
 
+> **Since, 0.15.0.** The stage was fixed (§ The reduced base, below), and the
+> draft was built anyway, in the form this section would accept: the develop
+> view renders at half resolution while a gesture moves and once at full
+> resolution 120 ms after it stops (`ui/dr-ui/src/refine.rs`), the histogram
+> dims while it describes an older frame, and the last draft fades out over
+> 150 ms rather than being swapped. It is not a mask over a slow stage; it
+> spares a drag the full-resolution frames it does not need.
+
 ---
 
 ## Which GPU, on a machine with more than one
@@ -431,3 +439,38 @@ difference between a quarter-scale and a half-scale base to 0.03 stops of peak
 excursion and 2% of frame reach. But it is a change in reach rather than only
 in cost, it is what a tile scheduler would be handed, and it is worth knowing
 that the number moved rather than discovering it later as a seam.
+
+---
+
+## The fit view, again — 2026-09-25
+
+**Status:** Measured in the commits named, not re-run for this file.
+
+Two changes to the fused path made the `fit` rows above cheaper again,
+each with its before and after in its commit message. Both were measured
+on the laptop RTX 3050 with its clocks held at 420/810 MHz by the power
+cap, on the synthetic 60 MP source of `examples/frame_budget.rs`, median of
+five alternated runs; both leave the rgba8 output bit-identical.
+
+**The source gather is read once per framing** (`1dc7b45`). At fit every
+output pixel reads one texel on a stride through a source three or four
+times its width, and that gather was most of the fused pass. The pass now
+keeps a render-sized `rgba16float` cache of it, keyed on the framing, and
+reads it back while only the adjustments move:
+
+| scene | before | after |
+|---|---:|---:|
+| neutral, 2560 × 1600 fit | 10.62 ms | 3.88 ms |
+| neutral, 3840 × 2160 fit | 21.05 ms | 7.11 ms |
+| clarity, 3840 × 2160 fit | 42.20 ms | 27.88 ms |
+| neutral, 2560 × 1600 1:1 (control) | 3.83 ms | 3.84 ms |
+
+An interpolated read (straightening, lens warps, CA) is not cached, and the
+cache is written on the second frame with a given key, so a crop or zoom
+drag pays nothing for it.
+
+**A detail pass that changes nothing is dropped** (`d430ec9`). Capture
+sharpening at a scale too coarse to draw its radius emits an empty pass,
+which cost a full read and write when another neighbourhood operation
+followed it: sharpen with clarity at 2560 × 1600 fit went from 18.66 ms to
+14.16 ms, and at 3840 × 2160 from 37.93 ms to 27.88 ms.

docs/dev/requirements.md

@@ -667,6 +667,12 @@ asynchronously, and the proxy result remains on screen until it is ready.
 quality or resolution, refining to full quality when interaction settles. Refinement is visually
 smooth, not a jarring swap.
 
+*Status (2026-09-26).* Met in 0.15.0. A gesture renders half-resolution drafts, and the sharp frame
+lands once, 120 ms after the last movement rather than on a timer counted from the first
+(`ui/dr-ui/src/refine.rs`). While a draft is up the histogram's display reading is dimmed, since it
+describes the last settled frame; the last draft is kept over the sharp one and faded out in
+150 ms, so the refinement is not a swap.
+
 **FR-DSP-5 — Zoom and pan.** Fit, 1:1, and arbitrary zoom levels. At 1:1 and above, the pipeline
 operates on the visible crop at full source resolution.