# GOL-028: Drifting Chains

Supported chains shed their oldest members as they grow. Travel by rotating compasses or fixed initial directions, and return dead travelers to their original locations.

[Open simulation](https://100gol.com/experiments/028) · [Directory](https://100gol.com/experiments)

## What to explore

Reveal recursive support, chain seniority, collective drift and return journeys.
Keep the source of each death and birth inspectable. Preserve whole-cohort ties
and no-winner conflicts, even when that removes more cells than capacity demands.

## Rules, update order and replay

Square Moore lattice including diagonals; 80/120/160 square, toroidal by default,
optionally bounded. Every living organism owns its original location, original
randomized heading, current compass, permanent rotation sense, private compass
clock and first chain-entry generation (minus one before qualification). Sites
own seeded birth streams. Generation and previous source/site evidence complete
the replay state. Origins and headings travel with life; empty positions carry
no organism state. No global body identity determines age or priority.

Each Step freezes the starting field. Empty sites propose ordinary birth when
at least X original living neighbors are present. Recursively peel living cells
with fewer than Z remaining contacts to obtain the Z-core. This uses whole-graph
knowledge; it is not one-ring-per-turn propagation. First-time core members receive
the current generation as chain entry. Existing tenure persists through movement,
merges, splits, rule edits and blocked movement. Birth time is not chain age.

Partition the core into connected groups. At or below Y members, including self,
remove nobody for capacity. Above Y, remove oldest chain-entry cohorts until the
remaining count is at most Y. Everyone tied at the cutoff dies; the removal can
exceed N minus Y. Merging chains compare their members' original tenure without
resetting either side. An oversized opening whose members all qualify together
can still die completely: that is an honest age tie. Prune support again after
capacity deaths, then recompute connected components. Cascading losses and newly
separate movement bodies are explicit consequences, not forced preservation.

Every surviving component votes with equal unit vectors. Rotating compass mode
uses current compasses; straight-line mode uses original randomized headings.
Unchanged membership therefore maintains a straight heading even while private
compasses continue ticking in the background. Membership changes recompute the
mean. Choose the nearest Moore direction; exact zero and exact ties rest. Every
turn attempts one rigid one-cell shift. Own-footprint overlap is allowed; other
survivors, provisional newborns and bounded edges block. Competing feasible
proposals all fail. There is no retry, partial shearing, swap or following another
body's departure. Newly dead positions are available. Newborns first qualify and
move on the next Step. Mergers caused by this movement are assessed next Step.

With Home rebirth enabled, any organism killed by either pruning pass or capacity
away from its original location makes one return attempt after movement resolves.
Death while already at home produces no return. Final survivor/arrival occupancy
blocks; all competing claims on a home fail. A unique return replaces an ordinary
birth proposal at that home, never a survivor or accepted moving arrival. A home
vacated in this movement pass is available. Failed returns do not queue. All
return claims resolve together; no recursive death/rebirth runs within a Step.
A return preserves origin, original heading and permanent sense, resets current
compass to the original heading and its clock to zero, and clears chain tenure.
It acts next Step. Ordinary births and newly painted life receive a new home at
their creation site and fresh seeded traits. No persistent dead-entity population
or return queue accumulates. Manual erasure is editing and never causes rebirth.

Commit together. Existing survivors tick their private compass after voting,
even in straight-line mode or when blocked. Interval zero holds the compass;
otherwise advance by the configured 45-degree increments in the permanent sense.
Movement has no interval. Reset reconstructs occupancy, original homes, both
headings, senses, clocks, empty tenure and site streams. Clear removes life and
restarts streams. Rule/topology/painting edits pause and invalidate evidence;
compass interval edits additionally reset clocks. Changing movement mode or home
rebirth preserves living organisms and their memories. Complete replay includes
all arrays, seeds/streams, generation, rules, dimensions and topology.

## Reading the simulation

Canvas 2D: lime survivors, cream ordinary newborns, cyan moving arrivals, coral
blocked survivors and violet home rebirths. Color off shows binary occupancy.
The canvas accessible label separates ordinary births and home rebirths. Running
context stays static; pause for exact selected-cell evidence. Inspection shows
original neighbors, first/second pruning reasons, pre-trim group size, excess,
whole-cohort removals/cutoff, chain entry generation, original location/direction,
current compass/sense/clock, active vote histogram/resultant, source fate, home
return claims/blocking, next site occupancy and previous source/home-arrival
records. An arriving return's old position is preserved as site evidence.

Cyan outlines show the surviving body (or original capacity group for a removed
cell), coral its removals, violet dashes proposed destinations and the selected
organism's home. Arrow keys select; Enter paints; P plays/pauses; S steps. The
centered mobile randomize shortcut follows all instructions, uses the same rail
handler, and works with both panels closed.

## Reproduce a starting configuration

[Download example JSON](https://100gol.com/api/experiments/028/configuration). Import it using Share & reproduce in the simulation controls. It starts paused at Step zero. Files contain rules and initial conditions, not evolved boards or manual edits. See [format, limitations and automated access](https://100gol.com/agents).