STEP20C temporal rendering and damage probe

Status: EXPERIMENTAL / PROTOCOL RECORDED BEFORE FIXTURE. This probe uses private headless binaries only. STEP20C remains NEXT and multi-output Mosaic remains NOT YET SUPPORTED. No UX, production ABI, package or transaction contract is changed here.

Measured verdict: PARTIALLY_FEASIBLE for the sampled temporal matrix. The stabilized visual and lifecycle assertions passed in the runs below; frame-by-frame presentation, full input/render synchronization and native transaction generation remain unproven.

Question and prior evidence

The negative-origin probe found sampled popup clipping and hit testing feasible at stable positions. It did not capture every presented frame or prove SceneFX damage sufficiency. This probe asks whether repeated XDG lifecycle and camera transitions expose stale pixels, wrong input targets or scene/IPC disagreement. A successful settled screenshot cannot establish correctness during the transition.

Fixed geometry and three configurations

HEADLESS-1 is (-800,0,800,600), HEADLESS-2 is (0,0,800,600), scale 1, transform normal, global bounds [-800,800) × [0,600). PNG coordinates are output-local: HEADLESS-1 local X is global X plus 800, HEADLESS-2 local X is global X. The virtual pointer receives sent_x=global_x+800 with extent 1600×600; client enter/button events validate actual targeting.

Mode	Binary	Layout	Camera
A	unmodified `/usr/bin/sway`	`splith`	N/A
B	private Mosaic with private SceneFX	`splith`	N/A
C	same private binary, clip and owner guard	`mosaic`	400 ↔ 1280

Each run uses its own mode-0700 runtime, discovered private Wayland display, explicit swaymsg -s socket, bounded children and two-output captures. The daily session socket is excluded from the subprocess environment. The ordinary layout controls compare common XDG creation, input and destruction; they have no invented camera counterpart.

Hypotheses and XDG lifecycle

H1: hiding the fully off-viewport tiled owner removes its popup pixels. H2: camera return restores the same mapped A/B objects without old-position pixels. H3: after B then A are destroyed, their former regions show the underlying surfaces. H4: applied scene, clip, IPC and pointer targets agree at observed transitions. H5: SceneFX invalidates the regions actually changed. H6: private splith does not regress against unmodified SwayFX for common XDG transitions. H7: repetition produces no crash, protocol error, surface accumulation or ghost pixels. Each hypothesis receives its own verdict.

TOPLEVEL → POPUP_A → POPUP_B is a real parent chain with distinct wl_surface, xdg_surface and xdg_popup objects. Opening A uses a fresh TOPLEVEL button serial; opening B uses a fresh A button serial. Every popup gets role configure, xdg_surface ack, then buffer map. Explicit close destroys B first; A is destroyed after B. An outside click may deliver popup_done B then A and has a different expected outcome from camera hiding without a click. Serial values are per run, never constants.

State and observation boundaries

The logical Mosaic scroll_x in IPC is distinct from Sway pending/current container geometry and from the applied scene position. The owner applied rectangle, clip log and sampled PNGs must corroborate scene placement. An IPC success reply proves command acceptance, not presentation. The current private probe exposes no native transaction generation. SPIKE_DAMAGE records an output-local damage bounding extent before scheduling a frame and adding to the damage ring; it is neither an exact region decomposition nor proof of a presented frame. Any experimental counter must be labelled local. The run preserves monotonic action/capture times, IPC trees, pointer/client events, compositor logs and PNG hashes. grim produces sampled screenshots; it cannot guarantee capture of every presented frame or a fixed achieved frequency. Damage-to-pixel matching is PARTIAL unless records can be associated with the actual presented frame and capture.

Predefined scenarios and observations

The initial target is ten complete stable cycles per mode, bounded by a per-run duration and capture/byte limit. Each cycle gets a unique ID and:

Phase	Action and expected evidence
S0	no popup, verified outputs, static reference, IPC, two PNGs
S1	real TOPLEVEL click, A grab/configure/ack/map, two PNGs
S2	real A click, B grab/configure/ack/map, two PNGs
S3	visible A/B, configured/applied positions, interaction without dismissal
S4	C only: `scroll_x` 400 → 1280, fully hidden owner, A/B still mapped, no popup hit
S5	C only: 1280 → 400, same XDG objects, visible pixels restored
S6	explicit B close, A retained, formerly covered region restored
S7	explicit A close or controlled outside dismissal, underlying rendering restored
S8	no old popup objects, owner/client alive, prepare fresh serials

Separate runs cover controlled outside-click dismissal and Mosaic → splith with open popups. After stable cycles pass, target 15–20 camera back-and-forth transitions with A/B open, first with observed stabilization and then with rapid IPC requests. Record both request and observed states; coalescing is not automatically a failure. A reproducible crash stops the loop for minimal reproduction. Failed and inconclusive cases remain in the evidence.

Image and damage analysis protocol

Use the nested client's solid SHM A-yellow (224,192,32) and B-green (32,208,160) surfaces as known foreground. Establish stable reference images of the background and formerly covered A/B rectangles before scoring. Avoid dynamic wev text regions when comparing full pixels; any mask must be defined before looking at anomalies. Cursor, decorations, text, effects, capture compression and IPC/capture timing can create unrelated differences. Record each PNG's dimensions, monotonic capture timestamp, SHA-256, phase, output-local region of interest, exact popup-color count, whole-region diff count, diff bounding box and anomalous local coordinates. Compare formerly covered regions with the appropriate uncovered reference, not just the decrease of an exact color. Keep signed global conversion separate.

For each transition, compare observed changed regions with time-ordered SPIKE_DAMAGE extents for that output, then with the rendered result. A broad damage extent alone is not a correctness failure; missing or late invalidation requires synchronized evidence. When frame association is absent, mark H5 PARTIAL even if stabilized images are correct.

Verdict rules and limits

Each assertion is PASS only with the required geometry, XDG serial and lifecycle traces, mapped identities, client events, PNG pixels and process status. FAIL requires a demonstrated invariant violation. PARTIAL means some required observation exists but coverage or synchronization is limited. INCONCLUSIVE means the fixture cannot identify the behavior; NOT TESTED means it was not run. A zero process exit alone is never PASS.

The aggregate is FEASIBLE for the sampled temporal matrix only when all executed required visual/input transitions pass, controls have no blocking regression, and damage traces support only the precise claims made. Positive stabilized images with incomplete frame/damage association are PARTIALLY_FEASIBLE. A reproducible leak, protocol violation, destruction defect or crash is BLOCKED. Unusable fixture or captures are INCONCLUSIVE. Untested cells stay NOT TESTED. Scaling, rotation, resize, migration, complete effects and ABI/package maintenance are outside this experiment. No result authorizes production STEP20C or daily use.

Measured campaign and retained evidence

The final instrumented lab is /tmp/swayfx-mosaic-nested-grab-RbwDblky/ with build log /tmp/mtd-prepare-Rv5kR9sm. It contains ten runs: ten complete cycles each in unmodified SwayFX splith, private splith, and private Mosaic; one extra private Mosaic pilot cycle; one camera run; outside click runs in all three configurations; a distinct hidden-owner click; and a private Mosaic → splith return. The planned 30 cycles all completed. There are 994 sampled PNGs on two outputs. None is labelled a complete presented-frame sequence. The popup owner and A/B are solid SHM surfaces; supporting Kitty windows ran with cursor blinking disabled. The predefined HEADLESS-1 ROI (400,90,800,310) was empirically stable across S0 and post-close captures in the completed cycles. wev on HEADLESS-2 can redraw its text, so its whole image was not treated as a static underlay; right-output popup colors and events were checked separately. The ROI and this exclusion were fixed before scoring the campaign.

Observation	Unmodified `splith`	Private `splith`	Private Mosaic
Ten A/B open → close B → click A → close A cycles	PASS sampled	PASS sampled	PASS sampled
A right-button delivery after B destruction	10/10	10/10	10/10
Former A/B left-output ROI restored	10/10 exact equalities	10/10	10/10
B crossing color at right, cycles 1 and 10	15,860 green	15,860 green	0 green
Fully hidden A/B colors and camera return	N/A	N/A	10/10 sampled: 0/0 hidden, A/B restored with equal ROI
Outside-click `popup_done` and child-first destruction	PASS	PASS	PASS
Hidden-owner click: no popup button, B/A dismissal	N/A	N/A	PASS sampled
Stable `splith` return with B open	N/A	N/A	15,860 B pixels and actual B button
Damage/frame presentation proof	NOT TESTED	PARTIAL	PARTIAL

The camera run requested 18 outward/return pairs in each of three pacing modes: stabilization after every change, capture between accepted commands, and a four-command burst without intervening captures. The owner stayed IPC ID 8, A/B were created once each, no popup_done occurred before explicit closure, and the sampled hidden/visible colors followed the observed target values. All 109 camera_observed records, including initial positioning, reported targets 400 or 1280. No sampled right-output A/B color appeared. The runner's IPC checks do not prove which intermediate target values were actually presented. The burst may coalesce them. Input/render consistency during an unobserved frame is therefore PARTIAL, even though the sampled pointer and pixel outcomes show no reproducible divergence.

The separate hidden-click run sent a right button to a point on HEADLESS-1 after scroll_x=1280. The count of popup button presses did not increase; popup_done arrived B then A, and neither popup reappeared after return to 400. This is one controlled hidden point, not a universal input claim.

The private SceneFX TEMPORAL_DAMAGE log recorded 4,361 output-local damage extents across the eight private runs, and the actual SwayFX repaint path logged 1,432 accepted output commits (zero rejected). The analyzer compared each pair of sampled captures per output against extents whose monotonic timestamps fell in that capture interval. It found zero changed pixels outside their union and zero changed intervals without an overlapping extent. This is interval evidence only: broad bounding extents may hide over-invalidation, and no screenshot is tied to a unique presented frame. H5 is PARTIAL. The unmodified control has no private damage trace and is NOT TESTED for H5.

An independent audit of the retained PNGs compared all three RGB channels, rather than relying on the analyzer's grayscale difference. Across 784 private same-output capture intervals, 237 contained changed pixels (57,451,528 changed pixel positions in total); zero changed positions fell outside the union of their time-bounded logged damage extents. This confirms the narrowly stated interval observation despite the grayscale conversion used by the fixture analyzer. It does not establish minimal damage, exact pixman regions, a damage-to-commit mapping or intermediate frame correctness.

results/artifacts-sha256.txt lists 2,133 raw and derived files, with manifest SHA-256 362ba5dc399383ecd7c071b56c144b8bdf9f4dc17fad53b60238a14c750bdf7c. The final 12-input source manifest is temporal-source-sha256.txt, SHA-256 ef5596c587372388efedd9319ee0062cf1143e2a7c203ed4c579fc6346753702. The preceding instrumented lab /tmp/swayfx-mosaic-nested-grab-1u4Q8mE9/ retains its original temporal-source-sha256-initial.txt: after those runs, its analyzer gained a pixel-wise union check and final matrix. The final lab was rebuilt after the A-input and hidden-click refinement and carries a single matching source manifest. sha256sum -c passed for all 2,133 listed artifacts and all 12 final source inputs.

A fresh private lab at /tmp/swayfx-mosaic-nested-grab-u5ZlcX0A/ rebuilt the pinned source and patches and passed its 12-input source manifest. A targeted replay completed one A/B open → explicit B/A close cycle in each of the three configurations, plus private Mosaic hide/click/return, one two-move camera run and a separate outside-click dismissal. All six runs had no runner failure, valid XDG button serials and no failing targeted assertions. Their 124 sampled PNGs, 1,457 private timed damage extents and 289 accepted private output commits reproduce the sampled outcome; they do not add frame identity. This fresh lab is retained outside Git.

The independent uninstrumented lab /tmp/swayfx-mosaic-nested-grab-36Cbn4JP/ had the same ten-cycle sampled outcomes in each configuration. The first instrumented lab /tmp/swayfx-mosaic-nested-grab-M5uSSO6U/ and the later /tmp/swayfx-mosaic-nested-grab-1u4Q8mE9/ also repeated them. No probe-induced visual difference was observed in these sampled runs; timing perturbation outside them remains possible. No compositor crash, Wayland protocol error, failed grab, stale popup object or residual popup-colored pixel was detected in the completed final matrix. The initial toggle sampling failure and its correction are recorded in the history below.

This result does not settle popup UX while an owner is hidden, full transaction-generation consistency, all presented frames, effects/decorations, saved buffers, scaling/rotation, output migration/resize or SceneFX ABI/package maintenance. The next bounded STEP20C experiment should instrument an actual headless output presentation event together with applied camera/clip state and pointer target for one repeated hide/return transition. It should test the unobserved interval directly; it does not authorize a production fix.

Protocol history

2026-10-11: protocol written before the temporal fixture; targets and verdict rules above are prospective. Subsequent changes and measured results must be recorded here with their date and run paths.
2026-10-11: first private campaign in /tmp/swayfx-mosaic-nested-grab-36Cbn4JP/ completed ten cycles in each configuration, plus 18 camera transitions per mode, outside clicks and a layout-return pilot. The original runner/analyzer sources are retained in that lab's source-snapshot-v1/. Its immediate layout splith capture contained no right-output B pixels; the protocol now adds a stabilized capture and B click before classification. The camera runner also adds a separate command burst without captures between every accepted scroll. These changes affect measurement timing, not the private clip algorithm.
2026-10-11: SPIKE_DAMAGE lacks monotonic timestamps and an output commit marker. A separate private SceneFX logging patch is therefore planned for the next lab. It may log CLOCK_MONOTONIC nanoseconds, the damage extent, and a local experimental output-commit ordinal/result. It will not expose a native transaction generation, alter public headers or prove presentation by itself. Compare the instrumented result with the uninstrumented campaign for probe-induced changes.
2026-10-11: the first instrumented lab /tmp/swayfx-mosaic-nested-grab-M5uSSO6U/ retained 10 cycles per mode, 18 camera round trips in each of three pacing modes, outside clicks and a successful stable layout-return check. It logged damage but zero SceneFX commit-hook calls. Source audit found the actual call in private SwayFX sway/desktop/output.c; a separate logging-only Mosaic patch is now added to the next private lab. The initial toggle runner failure in /tmp/swayfx-mosaic-nested-grab-pX0BTADM/ was a left-side fixture sample after stable right-side pixels had already been captured; it was not a compositor or XDG failure. Its logs and exit code are retained.
2026-10-11: the private SwayFX commit-hook patch logged the repaint path actually used. Pixel-wise unions and matrix.json were added to the analyzer after the first complete instrumented campaign; its original analyzer hash was retained in temporal-source-sha256-initial.txt under that lab. Its own source and artifact manifests remain available.
2026-10-11: a final protocol refinement adds an explicit A right-button interaction after B's destruction in each cycle, and a separate hidden-owner outside-click run. Earlier cycles demonstrated A mapping and B creation via an A click, but did not directly recheck A input after B closed. The new run must not erase or relabel earlier evidence; its own manifest and run IDs will distinguish this stronger input check from the previous matrix.
2026-10-11: the refined campaign in /tmp/swayfx-mosaic-nested-grab-RbwDblky/ completed the 30-cycle matrix, camera modes and both outside-click contexts. Ten post-B A interactions per configuration and the separate hidden-click non-hit assertion passed. Its final source and artifact manifests validate the finished analysis. The verdict remains PARTIALLY_FEASIBLE because frames and native transaction generations remain unobserved.

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