Add retained AtomMachine families

[SandroMaglione]

Summary

• Add AtomMachine.family, bound family, and AtomMachine.familyChild for input-keyed machine atoms whose public projections retain the private bridge.
• Preserve readonly and writable atom types, equality, lazy registry startup, disposal, service requirements, and Effect key equality without a permanent strong cache on weak-reference runtimes.
• Add data-last root and child selectors with contextual path completion, then correct the React guide's Atom.family lifetime guidance.

Changeset

• Added or updated for a library or package-metadata change
• Not required because this PR does not change a publishable package

Validation

• pnpm check
• Automated type-performance measurement passed or was not required
• Automated runtime- and memory-performance measurement passed or was not required

[github-actions]

Type performance

Measured with TypeScript 6.0.3 and skipLibCheck=true.

Scenario	Base	PR	Difference
Effect only	55	55	0 (0.0%)
Import effect-machine	55	55	0 (0.0%)
Machine.states (3 states)	3,039	3,039	0 (0.0%)
Machine.make (3 states, 2 events)	10,787	10,787	0 (0.0%)
machine.handle (3 states, 2 transitions)	28,551	28,551	0 (0.0%)
fluent transition (10 named branches)	122,775	122,775	0 (0.0%)
fluent invocation (state-dependent Effect)	108,429	108,429	0 (0.0%)
machine.handle (depth 24)	207,970	207,970	0 (0.0%)
machine.handle (wide depth 16)	236,332	236,332	0 (0.0%)
machine.handle (parallel/history/choice)	144,812	144,812	0 (0.0%)
machine definition (3 independent implementations)	143,617	143,617	0 (0.0%)
machine exact input/output/error/services	129,873	129,873	0 (0.0%)
execution adapter readiness	136,469	136,469	0 (0.0%)

Marginal instantiations are measured against the matching setup without that API call:

Scenario	Base	PR	Difference
Import effect-machine	0	0	0
Machine.states (3 states)	2,984	2,984	0 (0.0%)
Machine.make (3 states, 2 events)	7,740	7,740	0 (0.0%)
machine.handle (3 states, 2 transitions)	17,764	17,764	0 (0.0%)
fluent transition (10 named branches)	112,498	112,498	0 (0.0%)
fluent invocation (state-dependent Effect)	99,018	99,018	0 (0.0%)
machine.handle (depth 24)	187,474	187,474	0 (0.0%)
machine.handle (wide depth 16)	217,043	217,043	0 (0.0%)
machine.handle (parallel/history/choice)	124,167	124,167	0 (0.0%)
machine definition (3 independent implementations)	127,576	127,576	0 (0.0%)
machine exact input/output/error/services	115,217	115,217	0 (0.0%)
execution adapter readiness	106,299	106,299	0 (0.0%)

Check times (informational)

Scenario	Base	PR
Effect only	0.03s	0.03s
Import effect-machine	0.03s	0.03s
Machine.states (3 states)	0.10s	0.11s
Machine.make (3 states, 2 events)	0.18s	0.18s
machine.handle (3 states, 2 transitions)	0.27s	0.28s
fluent transition (10 named branches)	0.61s	0.60s
fluent invocation (state-dependent Effect)	0.60s	0.60s
machine.handle (depth 24)	0.87s	0.90s
machine.handle (wide depth 16)	0.89s	0.89s
machine.handle (parallel/history/choice)	0.73s	0.71s
machine definition (3 independent implementations)	0.75s	0.73s
machine exact input/output/error/services	0.66s	0.66s
execution adapter readiness	0.69s	0.66s

Type instantiations are the comparison metric. Check time varies with runner load and is informational only.

[github-actions]

Runtime performance

Median of 5 independent benchmark processes on AMD EPYC 7763 64-Core Processor with Node v24.19.0.

Pull request baseline

Scenario	Effect Machine
Plan counter transitions	122,513 transitions/s
Drain burst with terminal fence	389,416 increments/s
Drain burst with a change observer	361,439 increments/s
Lookup and send to one child	314,969 increments/s
Start and stop a machine	142,796 machines/s
Start and stop a parent with one child	28,723 families/s
Plan transitions through a compound state	107,631 transitions/s
Plan transitions through parallel regions	87,405 transitions/s
Drain burst through a compound state	313,919 events/s
Drain burst through two parallel regions	317,679 events/s
Drain a compound-state burst with a change observer	297,955 events/s

Process runtime reference points

Scenario	Effect Machine
Start and stop a raw generic process	14,992 processes/s
Start and stop a raw compiled process	61,233 processes/s

Memory profile	Effect Machine
Idle machine	1.7 KiB
Raw generic managed process	13.9 KiB
Raw compiled process	3.1 KiB
Two independent idle machines	3.3 KiB
Idle parent with one child	5.7 KiB
Parent with observed child registry	9.8 KiB
Parent with observed invoked child snapshots	6.3 KiB

Effect Machine change from base

Metric	Base	Base variability	PR	PR variability	Difference
Plan counter transitions	123,290 transitions/s	0.5% MAD	122,513 transitions/s	1.5% MAD	-0.6%
Drain burst with terminal fence	382,088 increments/s	0.5% MAD	389,416 increments/s	1.4% MAD	+1.9%
Drain burst with a change observer	356,329 increments/s	0.5% MAD	361,439 increments/s	0.6% MAD	+1.4%
Lookup and send to one child	318,384 increments/s	0.7% MAD	314,969 increments/s	0.2% MAD	-1.1%
Start and stop a machine	142,592 machines/s	1.7% MAD	142,796 machines/s	0.6% MAD	+0.1%
Start and stop a parent with one child	28,543 families/s	4.5% MAD	28,723 families/s	3.0% MAD	+0.6%
Plan transitions through a compound state	106,274 transitions/s	0.4% MAD	107,631 transitions/s	1.1% MAD	+1.3%
Plan transitions through parallel regions	86,532 transitions/s	1.2% MAD	87,405 transitions/s	0.6% MAD	+1.0%
Drain burst through a compound state	315,446 events/s	0.8% MAD	313,919 events/s	2.2% MAD	-0.5%
Drain burst through two parallel regions	318,120 events/s	0.3% MAD	317,679 events/s	0.8% MAD	-0.1%
Drain a compound-state burst with a change observer	299,165 events/s	0.5% MAD	297,955 events/s	2.2% MAD	-0.4%
Idle machine heap per unit	1.7 KiB	0.0% MAD	1.7 KiB	0.1% MAD	+0.4%
Raw generic managed process heap per unit	13.9 KiB	0.0% MAD	13.9 KiB	0.0% MAD	+0.0%
Raw compiled process heap per unit	3.2 KiB	0.8% MAD	3.1 KiB	0.1% MAD	-0.8%
Two independent idle machines heap per unit	3.3 KiB	0.0% MAD	3.3 KiB	0.1% MAD	-0.0%
Idle parent with one child heap per unit	5.7 KiB	0.0% MAD	5.7 KiB	0.0% MAD	0.0%
Parent with observed child registry heap per unit	9.8 KiB	0.0% MAD	9.8 KiB	0.0% MAD	+0.0%
Parent with observed invoked child snapshots heap per unit	6.3 KiB	0.0% MAD	6.3 KiB	0.1% MAD	-0.1%

Process runtime reference change from base

Metric	Base	Base variability	PR	PR variability	Difference
Start and stop a raw generic process	15,162 processes/s	1.3% MAD	14,992 processes/s	1.1% MAD	-1.1%
Start and stop a raw compiled process	61,425 processes/s	0.6% MAD	61,233 processes/s	0.1% MAD	-0.3%

Regression guard

No large, noise-adjusted throughput or heap regressions detected.

Versions and interpretation

• Effect Machine: 0.27.1

Higher throughput is better; lower heap is better. Variability is the median absolute deviation across independent processes, relative to their median. Small differences on shared GitHub-hosted hardware remain informational; the required guard rejects only large changes beyond the measured noise allowance.