Introduce underground tunnel sections to Zuma levels, letting the
chain roll out of sight and back in. Tunnels are arc-length intervals
on the path; while a ball is submerged it is inert — ignored by shots,
the laser sight, and explosions — and the path itself is drawn as a
faint buried trace beneath any live section that crosses it.
Engine (ZumaLogic.js): TUNNEL constants, normalizeTunnels, isHidden,
visibilityAt, pathSpans, sampleRange, nearestS; createLevel,
syncPositions, applyPower, stepFlights, and rayHit all honour
submersion. validateLevel lints mouth placement, spacing, and the
40% max-hidden fraction.
Game (ZumaGame.js): depth layer reorg so a live path always wins an
overlap with a tunnel stone; addPortal draws the two-layer maw (stone
below the chain, mouth above it); drawPit replaces the old skull with
a broken-stone collar and vapour swirl; startPitFall rolls the lost
chain over the lip in order, shrinking marbles into the dark; the
level-start fanfare ducks the soundtrack via MusicPlayer pause/resume.
Editor (ZumaEditor.js): new Tunnels tool with click-to-place,
drag-to-slide, right-click-to-remove, ESC-to-cancel; three graphics
layers (buried path, live path, handles) matching the game's
stacking; queueGameAssets so editor Test Play has the lazy art ready.
Art: ZumaPortal.js (carved serpent-head maw, symmetric so one
texture serves both ends) and ZumaPit.js (shaft of darkening discs
read as depth, not a painted circle).
Audio: four Zuma SFX (shoot, hit, start, explode) and a three-track
soundtrack wired through data/zuma-music.json and the asset manifest;
genZuma.js gains a tunnels column (fractions of path length) and
verifyZuma.js gains a tunnel test suite.
