Compact invoke session bookkeeping

[SandroMaglione]

Summary

• Replace the invoked-child session Ref and persistent HashMap with one compact runtime-owned Map.
• Keep every session mutation deferred inside synchronous Effects so reservation, removal, stale-token checks, and bulk shutdown remain atomic between fiber steps.
• Preserve path-scoped invoke identity, child stop ordering, and stale callback protection while removing two Effect data structures from every invoke-capable machine.

Changeset

• Added or updated for a library or package-metadata change
• Not required because this PR does not change src/ or package.json

Validation

• pnpm check
• Relevant example checks, when examples changed (no examples changed)
• Reviewed the automated type-performance report, when the public TypeScript API or inference changed (no public API change; local budgets pass)
• Reviewed the automated runtime-performance report, when runtime behavior changed

CI confirms parent with one child lifecycle +2.0%, family heap -0.4%, and observed-family heap -0.3%; standalone memory controls remain flat.

[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.defineStates (3 states)	2,965	2,965	0 (0.0%)
Machine.make (3 states, 2 events)	8,715	8,715	0 (0.0%)
machine.handle (3 states, 2 transitions)	23,492	23,492	0 (0.0%)
machine.handle (depth 8)	117,075	117,075	0 (0.0%)
machine.handle (depth 12)	129,713	129,713	0 (0.0%)
machine.handle (depth 16)	145,055	145,055	0 (0.0%)
machine.handle (depth 24)	183,851	183,851	0 (0.0%)
machine.handle (wide depth 16)	214,189	214,189	0 (0.0%)
machine.handle (parallel/history/choice)	132,667	132,667	0 (0.0%)
machine.handle (4 successive calls)	128,674	128,674	0 (0.0%)
machine exact input/output/error/services	110,584	110,584	0 (0.0%)
execution adapter readiness	127,854	127,854	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.defineStates (3 states)	2,910	2,910	0 (0.0%)
Machine.make (3 states, 2 events)	5,742	5,742	0 (0.0%)
machine.handle (3 states, 2 transitions)	14,777	14,777	0 (0.0%)
machine.handle (depth 8)	109,601	109,601	0 (0.0%)
machine.handle (depth 12)	121,039	121,039	0 (0.0%)
machine.handle (depth 16)	135,181	135,181	0 (0.0%)
machine.handle (depth 24)	171,577	171,577	0 (0.0%)
machine.handle (wide depth 16)	202,224	202,224	0 (0.0%)
machine.handle (parallel/history/choice)	114,331	114,331	0 (0.0%)
machine.handle (4 successive calls)	113,703	113,703	0 (0.0%)
machine exact input/output/error/services	100,670	100,670	0 (0.0%)
execution adapter readiness	102,092	102,092	0 (0.0%)

Check times (informational)

Scenario	Base	PR
Effect only	0.03s	0.03s
Import effect-machine	0.03s	0.03s
Machine.defineStates (3 states)	0.09s	0.09s
Machine.make (3 states, 2 events)	0.15s	0.15s
machine.handle (3 states, 2 transitions)	0.21s	0.23s
machine.handle (depth 8)	0.47s	0.48s
machine.handle (depth 12)	0.51s	0.53s
machine.handle (depth 16)	0.55s	0.57s
machine.handle (depth 24)	0.64s	0.63s
machine.handle (wide depth 16)	0.69s	0.69s
machine.handle (parallel/history/choice)	0.56s	0.58s
machine.handle (4 successive calls)	0.55s	0.55s
machine exact input/output/error/services	0.47s	0.47s
execution adapter readiness	0.53s	0.52s

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 v24.18.0.

Pull request baseline

Scenario	Effect Machine	XState 5	XState 6 alpha
Plan counter transitions	106,800 transitions/s	134,171 transitions/s	122,420 transitions/s
Drain burst with terminal fence	73,459 increments/s	402,907 increments/s	112,461 increments/s
Drain burst with a change observer	57,549 increments/s	399,981 increments/s	112,087 increments/s
Lookup and send to one child	67,299 increments/s	397,328 increments/s	106,707 increments/s
Start and stop a machine	11,797 machines/s	182,815 machines/s	72,961 machines/s
Start and stop a parent with one child	4,151 families/s	67,536 families/s	26,702 families/s

Memory profile	Effect Machine	XState 5	XState 6 alpha	Effect runtime primitives
Idle machine	14.8 KiB	3.8 KiB	6.1 KiB	—
Raw managed process	13.2 KiB	—	—	—
Two independent idle machines	28.9 KiB	7.3 KiB	11.8 KiB	—
Idle parent with one child	36.8 KiB	5.5 KiB	8.8 KiB	—
Parent with observed child registry	48.2 KiB	—	—	—
Parent with observed invoked child snapshots	37.0 KiB	—	—	—
Suspended Effect fiber	—	—	—	0.7 KiB
Effect queue with waiting fiber	—	—	—	2.8 KiB
Effect mailbox actor shell	—	—	—	3.2 KiB

Effect Machine change from base

Metric	Base	Base variability	PR	PR variability	Difference
Plan counter transitions	108,866 transitions/s	1.6% MAD	106,800 transitions/s	0.7% MAD	-1.9%
Drain burst with terminal fence	74,009 increments/s	1.7% MAD	73,459 increments/s	0.9% MAD	-0.7%
Drain burst with a change observer	57,724 increments/s	1.6% MAD	57,549 increments/s	0.0% MAD	-0.3%
Lookup and send to one child	67,509 increments/s	1.3% MAD	67,299 increments/s	0.7% MAD	-0.3%
Start and stop a machine	11,829 machines/s	2.4% MAD	11,797 machines/s	0.7% MAD	-0.3%
Start and stop a parent with one child	4,068 families/s	0.9% MAD	4,151 families/s	0.8% MAD	+2.0%
Idle machine heap per unit	14.8 KiB	0.0% MAD	14.8 KiB	0.0% MAD	-0.0%
Raw managed process heap per unit	13.2 KiB	0.0% MAD	13.2 KiB	0.0% MAD	-0.0%
Two independent idle machines heap per unit	28.9 KiB	0.0% MAD	28.9 KiB	0.0% MAD	-0.0%
Idle parent with one child heap per unit	36.9 KiB	0.0% MAD	36.8 KiB	0.0% MAD	-0.4%
Parent with observed child registry heap per unit	48.3 KiB	0.0% MAD	48.2 KiB	0.0% MAD	-0.3%
Parent with observed invoked child snapshots heap per unit	37.1 KiB	0.0% MAD	37.0 KiB	0.0% MAD	-0.4%

Versions and interpretation

• Effect Machine: 0.3.0
• XState 5: 5.32.5
• XState 6 alpha: 6.0.0-alpha.27
• Effect runtime primitives: 4.0.0-beta.105

Higher throughput is better; lower heap is better. Variability is the median absolute deviation across independent processes, relative to their median. Runtime measurements on shared GitHub-hosted hardware remain informational, so small differences should be confirmed across multiple workflow runs.