iris: the fling curve was the identity function, and the keyboard was a targetSdk

Iris's 2026-09-07 phone report on ed04d4c: the resume glyph corruption is
fixed (item 4 closed with her evidence), flinging "seems to just be linear
velocity with an abrupt stop", and the keyboard still does not push
anything up. docs/RUST.md's new "The 2026-09-07 phone report" section has
the derivation and every number.

**The fling was arithmetically linear.** `android_fling_spline::
distance_fraction(t)` returned `t` for every `t`. Two halves of AOSP's
`SplineOverScroller` static initialiser had been transposed -- the
bisection solved the tension curve and the sample evaluated the P1/P2 one,
where AOSP does the opposite -- which made SPLINE_POSITION and SPLINE_TIME
identical; the lookup then bracketed `t` between SPLINE_TIME entries
instead of between even time steps, and the two cancelled to the identity.
Ported exactly now from OverScroller.java and androidx.compose.animation
1.12.0's SplineBasedDecay.kt, which agree line for line, as one table
indexed by even steps of time (AOSP's second table serves only
`adjustDuration`, which nothing here has, so it is deliberately not built
-- one array, one indexing rule). `FlingCalculator::velocity_at` is new
beside `position_at`, and `List::tick_fling` logs `iris fling tick:` with
the per-frame delta and speed.

Every existing test compared the calculator with itself -- monotonic,
signed, integrates to the closed form, deltas non-increasing -- and all of
them pass on a straight line. iris/benches/fling_spline_reference.py is an
independent hand transcription of both sources and supplies the numbers
now checked into `the_spline_matches_aosps_own_table` and
`a_flick_decelerates_the_way_aosp_says_it_does`;
`tick_fling_applies_shrinking_incremental_deltas` went from
"non-increasing" to "the last delta is under 80% of the first". Negative
control: with `sample` forced back to `t`, exactly those three fail.

Emulator (API 36, debug, force-gles): a released v=3750 decelerates
3746 -> 2624 -> 1834 -> 1144 -> 752 -> 449 -> 243 -> 83px/s over 32 frames
to t=0.664s; a flick into the end of the list stops there in one tick with
no overshoot; a tap 200ms into a fling ends it at 11 ticks.

**The keyboard: `targetSdk = 34`** in iris/android-app/app/build.gradle,
against compileSdk 37 and the Compose app's 37 -- and that app's keyboard
does push up on her phone. Below target 35 a window keeps the legacy
behaviour where adjustResize shrinks it for the IME, so
getInsets(ime()).bottom measures an already-shrunk window and is zero;
setDecorFitsSystemWindows(false) opts out of that and still takes on the
API 36 emulator here, which is why every test run passed. Now targetSdk 37.

That is a reading and not a measurement, so the other half is making the
phone able to answer it. MainActivity also registers a
WindowInsetsAnimation.Callback (onEnd re-reads getRootWindowInsets, so an
interrupted animation cannot freeze a value), which delivers the height
where only the animation path carries it and makes the push-up animate:
ime_bottom now arrives 509, 663, 833, 881, 883 instead of one jump.
`insets::Shared::updates` counts every dispatch and
`AndroidUiState::insets_report()` puts it in the Diagnostics pane --
screenshot-verified, `insets: dispatches=27 left=0 top=142 right=0
bottom=63 ime_bottom=0 ime_visible=false`. Iris has no logcat, and "the
listener never fired" and "it fired with a zero height" are otherwise the
same picture; dispatches=0 says so in words rather than showing defaults.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

docs/RUST.md

@@ -115,6 +115,129 @@ velocity and a moved scroll offset; one command opens the same screen in
 a phone-shaped window and screenshots it. Record the commands here when
 it lands.
 
+### The 2026-09-07 phone report on `ed04d4c`: the fling was linear, and the keyboard is a targetSdk
+
+Iris's three lines on the `ed04d4c` build (Pixel 9 Pro XL, GrapheneOS
+Android 17, Mali-G715, `content_scale` 2.55, 120Hz): item 4 (the resume
+glyph corruption) **is fixed**, confirmed on the phone; "flinging now does
+technically do something, but it seems to just be linear velocity with an
+abrupt stop"; and "similarly, the keyboard raising up does not push things
+upwards."
+
+**The fling was exactly, arithmetically linear.** Not approximately.
+`android_fling_spline::distance_fraction(t)` returned `t` for every `t`,
+which is a constant-speed slide for the full `duration()` and then a stop
+at full distance -- Iris's sentence, read straight off the code. Two
+transposed halves of one AOSP loop did it, and they compounded:
+
+1. AOSP's `SplineOverScroller` static initialiser **solves** the bisection
+   on the `P1`/`P2` curve and **samples** `SPLINE_POSITION[i]` from the
+   tension curve (`coef * ((1-x) * START_TENSION + x) + x³`); the second
+   half of the loop does the reverse to build `SPLINE_TIME`. iris had both
+   halves solving on the tension curve and sampling `P1`/`P2` -- so its two
+   loops were the *same computation*, and `SPLINE_POSITION == SPLINE_TIME`
+   element for element.
+2. The lookup then bracketed `t` between **`SPLINE_TIME` entries** and
+   interpolated `SPLINE_POSITION`. AOSP brackets between the even time
+   steps `index / N` and `(index + 1) / N` (`SPLINE_TIME` is used only by
+   `adjustDuration`, which iris has no analogue of). With the two arrays
+   identical, `d_inf + (d_sup - d_inf)(t - t_inf)/(t_sup - t_inf)` reduces
+   to `t_inf + (t - t_inf)` = `t`.
+
+Every test the calculator had compared it with itself -- monotonic, signed,
+integrates to the closed form, per-tick deltas non-increasing -- and all of
+them pass on a linear curve. That is the shape to distrust: `<=` is not
+deceleration.
+
+**Sources, read rather than remembered.** `frameworks/base`
+`core/java/android/widget/OverScroller.java` from
+`android.googlesource.com` (`?format=TEXT`, base64), and
+`androidx.compose.animation:animation:1.12.0`'s `SplineBasedDecay.kt` and
+`FlingCalculator.kt` out of the `-sources.jar` on
+`dl.google.com/dl/android/maven2` (there is no androidx checkout here and
+`cs.android.com` is JS-only; `androidx.tech` is now a parked domain serving
+an unrelated site). The two agree line for line, which is why iris ports
+one curve rather than two. The formulas, for the record:
+
+    P1 = START_TENSION * INFLEXION            = 0.5 * 0.35
+    P2 = 1 - END_TENSION * (1 - INFLEXION)    = 1 - 1 * 0.65
+    SPLINE_POSITION[i]: solve coef*((1-x)P1 + xP2) + x³ = i/100 for x,
+                        then take coef*((1-x)ST + x) + x³
+    physical_coeff = 9.80665 * 39.37 * density * 160 * 0.84
+    l              = ln(0.35 * |v| / (0.015 * physical_coeff))
+    distance       = 0.015 * physical_coeff * exp(rate/(rate-1) * l)
+    duration       = exp(l / (rate - 1)),  rate = ln(0.78)/ln(0.9)
+    at time t:  index = floor(100 * t/duration)
+                vcoef = (POS[index+1] - POS[index]) * 100
+                position = distance * (POS[index] + (t/duration - index/100) * vcoef)
+                speed    = vcoef * distance / duration
+
+**What changed.** `iris/src/sense.rs`'s `android_fling_spline` builds one
+table, indexed by even time steps, and `sample(t)` answers AOSP's
+`distanceCoef`/`velocityCoef` pair; `FlingCalculator` gained `velocity_at`
+beside `position_at`. `iris/benches/fling_spline_reference.py` is an
+independent hand transcription of both sources and prints the numbers the
+tests assert on -- checked in because "numbers computed by the code under
+test" is exactly how the last three tests passed through this defect.
+Tests: `the_spline_matches_aosps_own_table` (the curve is not the
+identity: 27.4% of the distance at a tenth of the time, 85.8% at half),
+`a_flick_decelerates_the_way_aosp_says_it_does` (11064px/s at density
+2.55: 6334px over 1.636s, speed 9202 -> 4733 -> 2650 -> 951px/s), and
+`tick_fling_applies_shrinking_incremental_deltas` strengthened from
+"non-increasing" to "the last delta is under 80% of the first". **Negative
+control run**: with `sample` forced back to returning `t`, exactly those
+three fail and the other eleven pass.
+
+**Emulator evidence (API 36 AVD, debug, `force-gles`, 2026-09-07).** A
+`ui-trace` swipe of 900px in 120ms releases at `v=3750` and the new
+`iris fling tick:` debug line reports, frame by frame,
+`speed=-3746 -> -2624 -> -1834 -> -1144 -> -752 -> -449 -> -243 -> -83px/s`
+over 32 frames ending at `t=0.664s`, with the per-frame `dy` falling
+`94 -> 34 -> 20 -> 13 -> 8 -> 4.4px`. **The end**: the same flick in the
+other direction, from a list already at its newest end, produces exactly
+one tick and stops -- no overshoot. **A finger during a fling**: swipe,
+then a tap 200ms later, ends the fling at `t=0.248s` and 11 ticks instead
+of running its full 0.55s.
+
+**The keyboard: the bench app targeted SDK 34.** `app/build.gradle` said
+`targetSdk = 34` while `compileSdk` was 37 and the Compose app in `app/`
+targets 37 -- and that Compose app's keyboard *does* push its transcript up
+on Iris's phone. Below target 35 a window keeps the legacy behaviour, where
+`adjustResize` shrinks the window for the IME so `getInsets(ime()).bottom`
+measures the overlap with an already-shrunk window and is zero;
+`MainActivity`'s `setDecorFitsSystemWindows(false)` opts out of that and
+still takes on the API 36 emulator here, which is why every test run showed
+the push-up working. It is deprecated as of API 35 and Android 17 is where
+it appears no longer to. Fixed by `targetSdk = 37`, where edge-to-edge is
+not opt-in.
+
+That is a *reading*, not a measurement -- no Android 17 device is reachable
+from here -- so the second half of the change is making the phone able to
+answer it. `MainActivity` now also registers a
+`WindowInsetsAnimation.Callback` (`DISPATCH_MODE_CONTINUE_ON_SUBTREE`,
+`onProgress` forwarding, `onEnd` re-reading `getRootWindowInsets` so an
+interrupted animation cannot leave a frozen value), which delivers the IME
+height on devices where only the animation path carries it and, on every
+device, makes the push-up *animate* with the keyboard: the emulator log now
+shows `ime_bottom=509, 663, 833, 881, 883` instead of one jump to 883. And
+`insets::Shared::updates` counts every dispatch, which
+`AndroidUiState::insets_report()` puts in the **Diagnostics pane**:
+
+    insets: dispatches=27 left=0 top=142 right=0 bottom=63 ime_bottom=0 ime_visible=false
+
+Screenshot-verified on the emulator. Iris has no logcat, and "the listener
+never fired" and "it fired with a zero height" look identical on screen;
+`dispatches=0` prints its own sentence instead of the numbers, since those
+would be defaults rather than measurements.
+
+**What to look at on the next build.** Open the keyboard, press
+`Diagnostics`, screenshot the `insets:` line. `ime_bottom` in the hundreds
+with the composer risen: fixed. `dispatches` climbing but `ime_bottom=0`:
+the targetSdk reading was wrong and the window is still being resized.
+`dispatches=0`: the listener is not being called at all, which is a
+different fault from either. For the fling, a flick should now visibly
+slow before it stops rather than running out at speed.
+
 ### The 22:16 phone report, worked 2026-09-06/07
 
 Iris's four items are listed in docs/IRIS_TODO.md's "From the phone,