feat(scene): reusable zab-transition Canvas scene (white + centered Zab logo) + A→transition→B playout

[ClodoCapeo]

What

The M10 transition built as a reusable static Canvas/LSML scene (data), not transition code — and a franc-cut A→transition→B playout. No lower_wipe_cover, no compiler change, no fade. Refs #79.

The scene — scripts/fixtures/zab-transition.lsml.json

• A franc full-screen white frame (background:#FFFFFF, 100%×100%) with a centred image child (the Zab logo) inside a stack (align/justify: center).
• Logo = LogoZab---BW.jpg (128×128, B&W on white) embedded as a base64 data:image/jpeg data-URI in image.src — no asset hosting, no Solar rebuild (the fast-track). B&W-on-white blends into the white frame.
• STATIC: no keyframes, no wipe-cover element, no scene_control leaf, no operator_inputs — the dormant lower_wipe_cover path is genuinely unused. Round-trips as plain LSML 1.1; props are spread at the node top level (the Orion lsmlNode form the @lumencast/runtime frame/stack/image primitives read flat off resolved.*).

The playout — scripts/probe-m10-canvas-live.py --transition-scene

• 3 OBS scenes: scene-screen-1 / scene-screen-2 (WGC monitor_capture, reused feat(harness): force WGC capture method + migrate Orion scene default to overlay shape (#78) #84 setup) + scene-transition (a browser_source rendering the active Orion zab-transition scene).
• Cuts A → transition → B in two bare SetCurrentProgramScene with a hold (--hold-ms, default 700ms). No SetCurrentSceneTransition ever (C-MECH). MID frame checked near-white+logo (not magenta, not black).
• --no-broadcast (dry) / --broadcast and C-SEC token redaction preserved.

Verified (no VPS / no desktop)

• 28 offline tests green (test_zab_transition.py new + test_m10_setup.py + test_probe_m10_real_orion.py); full offline set 87 green.
• Fixture is valid LSML 1.1, round-trips, the logo data-URI decodes to the exact complete image.
• Live smoke on a built pulsar.exe: the 3 scenes + 2 franc cuts fire, C-MECH holds (['SetCurrentProgramScene','SetCurrentProgramScene'], zero native-transition requests), C-CUT flips through all three, C-SEC clean.
• detect-secrets: the embedded logo data-URI introduces zero new findings (compliance gate clear).

Not done here (by design)

• The real CEF-of-Solar render of the white+logo scene (the MID stays black on a headless box — CEF doesn't paint a browser_source without an interactive desktop; --allow-blank defers it). That is Keeper's antenna run.
• The push+activate of zab-transition on the real Orion (the m8/m9 toolkit author leg is still gated/absent on main).

Surface sensitivity

Not a sensitive surface (no auth/secrets/network/deps changes). The only entropy concern — the embedded base64 logo — was checked against detect-secrets and is clean.

Note for Eleven

• The branch was cut from origin/main, which does not carry the two prior-branch commits (--real-orion nested ?token= URL + string-JSON leaf decode) from forge/pulsar-m10-real-orion-url-fix. My diff is purely additive and self-contained; offline tests + live smoke pass on the main base. If those url-fix commits land first, no conflict is expected (disjoint code).

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