# Colored decay (Milestone 6, issue #68)

Legacy defines seven decay block-state colors and has a texture/model for every one: black, red, green, blue, purple, yellow, and white. That does not mean all seven are active instability hazards. Its active provider deck registers blue, purple, red, and white. Black has a decay handler and provider class, but its provider registration is commented out; green and yellow have visual states without registered spread handlers. Rivencraft currently implements the four active provider colors. Their 16×16 textures are exact copies of the local Mystcraft 1.12.2-0.13.7.06 assets at `assets/mystcraft/textures/blocks/decay_{blue,purple,red,white}.png`. Legacy's `blockdecay.json` and `blockdecay_*.json` map these to cube-all models; Rivencraft uses the same mapping.

The local Legacy bytecode (`EffectDecayBasic`, `DecayHandlerSpreading`, and the four color handlers) seeds decay in a chunk, then spreads to six neighbors. Blue prefers softer blocks, red uses explosion resistance, purple is slower, and white converts almost anything and damages entities on contact. Rivencraft preserves the four colors, six-neighbor growth, relative conversion tendencies, and white contact damage. It adapts the exact difficulty formulas to modern block hardness and safety checks; fluids are not replaced, and provider attempts are deterministic from the Age seed and persisted attempt counter.

Decay requires both `instability.world_mutation=true` and `instability_decay.enabled=true` in the server config. Both now default to true, matching Legacy's enabled-by-default Age instability and provider registration. Existing config files retain their saved values, including `false`; change them explicitly to opt in after updating an existing installation. At most `instability_decay.max_attempts_per_call` neighbors (default four) are examined, each within radius one, and at most one block can be replaced per provider run. The shared Age action budget may lower that further. Only chunks already loaded and supplied by the scheduler are touched; no cross-dimension or force-loading path exists. A per-Age `rivencraft_decay` saved data file stores a bounded frontier (1024 positions per color) and attempt counter. Disabling decay stops seeding, spreading, and white contact damage; existing blocks remain so re-enabling can resume.

Decay rejects the saved Age spawn and its nearby 5×5 arrival platform (with a two-block margin), block entities, fluids, unbreakable blocks, vanilla portal/command/structure infrastructure, blocks in `#minecraft:portals`, all non-decay Rivencraft blocks, and blocks in `#rivencraft:decay_protected`. Data packs can append other mods' protected blocks to that tag. A fake-player break event is posted before replacement, and a placement event after it; a cancellation prevents or restores the change. As with other fake-player automation, protection mods need to handle NeoForge block events for this safeguard to apply.

GameTests cover persistence, frontier deduplication, selected-chunk limits, and Overworld isolation. A real-client check should enable both settings in a disposable Age, observe growth, leave/reload that Age, then disable decay and verify growth stops. Also test a claim-protected block and a block entity if a protection mod is installed.

For current test builds, an operator standing in an Age can use `/rivencraft age decay pulse white 32` (or `blue`, `purple`, `red`). This performs at most 32 budgeted provider calls in the player's already-loaded chunk and reports how many blocks converted. It does not edit the saved Age plan or instability score. Repeat the command to observe spread, leave/reload the Age to check persistence, then disable decay and confirm the command refuses to act. This test hook remains useful because the provisional authored-page scoring does not yet provide a reliable route to the Legacy eating deck's 15,000-point gate.