[SandroMaglione]

Summary

• MachineState accepts a child bridge (machine.child(Descriptor)) as well as a machine bridge. Paths and the children snapshot are typed by the child machine (ChildMachineAtom.State<A>), and inactive also renders while the state that owns the child is not active. MachineStateProps is now MachineStateProps<A, Path>, with MachineStateProps.Bridge and MachineStateProps.State<A>.
• Export useMachineResult(atom): the non-suspending, hydration-safe reader behind MachineState (server value during SSR and hydration, keeps the last Success while the atom is Initial again) for custom readers of select, matches, can, and other result atoms.
• createMachineContext factories can declare a second, Layer-typed parameter for per-owner capabilities. The Provider then requires a layer prop of exactly that type (and rejects it otherwise); like input, it is read once when the owner mounts. Factories that need a layer but no input declare the first parameter as void. New MachineContext.Args and MachineContext.ProviderProps<Args> types.
• Add AtomMachine.isMachineAtom to tell machine bridges from child bridges; MachineState uses it to choose selectSnapshot or selectSnapshotChild.
• Tests: child hydration (server-planned child state, DOM node identity and focus survive the parent starting, no console.error), inactive owner state renders inactive, useMachineResult never returns Initial after a Success during startup, per-owner layers (independent implementations per Provider, layer read once per React key). Typetests for child paths and snapshots, useMachineResult, layer required/rejected, and a layer missing the machine's service being a compile error.
• Docs: React guide "Per-owner capabilities" gains the createMachineContext form; render and child sections document child bridges and useMachineResult; React README updated.

Changeset

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

minor for @typeonce/effect-machine and @typeonce/effect-machine-react (fixed group).

Validation

• pnpm check (format check via dprint with the pinned plugin versions locally; packages/devtools/test/StaticSite.test.ts times out locally on unchanged main as well)
• Automated type-performance measurement passed or was not required
• Automated runtime- and memory-performance measurement passed or was not required

pnpm test:types, pnpm perf:types, and pnpm perf:runtime ran locally. The widened MachineState adds a negligible number of instantiations to the existing React typetest scenarios compared with main.

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Generated by Claude Code

[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.state (3 children)	2,664	2,664	0 (0.0%)
Machine.make (3 states, 2 events)	8,932	8,932	0 (0.0%)
machine.handle (3 states, 2 transitions)	39,449	39,449	0 (0.0%)
declared transition (10 named branches)	60,402	60,402	0 (0.0%)
atomic construction, guards, and reentry	85,710	85,710	0 (0.0%)
registered invocation (input-taking Effect)	39,819	39,819	0 (0.0%)
machine.handle (depth 24)	194,531	194,531	0 (0.0%)
machine.handle (wide depth 16)	218,238	218,238	0 (0.0%)
machine.handle (parallel/history/choice)	91,642	91,642	0 (0.0%)
machine definition (3 independent implementations)	99,173	99,173	0 (0.0%)
machine exact input/output/error/services	82,941	82,941	0 (0.0%)
execution adapter readiness	71,428	71,428	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.state (3 children)	2,609	2,609	0 (0.0%)
Machine.make (3 states, 2 events)	6,260	6,260	0 (0.0%)
machine.handle (3 states, 2 transitions)	30,517	30,517	0 (0.0%)
declared transition (10 named branches)	51,849	51,849	0 (0.0%)
atomic construction, guards, and reentry	70,370	70,370	0 (0.0%)
registered invocation (input-taking Effect)	32,682	32,682	0 (0.0%)
machine.handle (depth 24)	177,222	177,222	0 (0.0%)
machine.handle (wide depth 16)	201,707	201,707	0 (0.0%)
machine.handle (parallel/history/choice)	79,144	79,144	0 (0.0%)
machine definition (3 independent implementations)	88,492	88,492	0 (0.0%)
machine exact input/output/error/services	70,732	70,732	0 (0.0%)
execution adapter readiness	31,922	31,922	0 (0.0%)

Check times (informational)

Scenario	Base	PR
Effect only	0.02s	0.02s
Import effect-machine	0.02s	0.02s
Machine.state (3 children)	0.06s	0.07s
Machine.make (3 states, 2 events)	0.10s	0.10s
machine.handle (3 states, 2 transitions)	0.22s	0.22s
declared transition (10 named branches)	0.30s	0.30s
atomic construction, guards, and reentry	0.37s	0.37s
registered invocation (input-taking Effect)	0.22s	0.23s
machine.handle (depth 24)	0.45s	0.45s
machine.handle (wide depth 16)	0.49s	0.49s
machine.handle (parallel/history/choice)	0.37s	0.37s
machine definition (3 independent implementations)	0.38s	0.38s
machine exact input/output/error/services	0.37s	0.34s
execution adapter readiness	0.32s	0.32s

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 v24.21.0.

Pull request baseline

Scenario	Effect Machine
Plan counter transitions	116,623 transitions/s
Drain burst with terminal fence	403,005 increments/s
Drain burst with a change observer	376,380 increments/s
Lookup and send to one child	329,677 increments/s
Start and stop a machine	117,841 machines/s
Start and stop a parent with one child	23,282 families/s
Complete an Effect invocation with tracing enabled	7,086 invocations/s
Complete an Effect invocation with tracing disabled	8,659 invocations/s
Plan transitions through a compound state	104,047 transitions/s
Plan transitions through parallel regions	82,084 transitions/s
Drain burst through a compound state	344,930 events/s
Drain burst through two parallel regions	317,580 events/s
Drain a compound-state burst with a change observer	320,324 events/s

Process runtime reference points

Scenario	Effect Machine
Start and stop a raw generic process	19,867 processes/s
Start and stop a raw compiled process	69,266 processes/s

Memory profile	Effect Machine
Idle machine	1.9 KiB
Raw generic managed process	11.7 KiB
Raw compiled process	3.1 KiB
Two independent idle machines	3.5 KiB
Idle parent with one child	6.0 KiB
Parent with observed child registry	9.5 KiB
Parent with observed invoked child snapshots	6.9 KiB

Effect Machine change from base

Metric	Base	Base variability	PR	PR variability	Difference
Plan counter transitions	116,801 transitions/s	2.5% MAD	116,623 transitions/s	2.1% MAD	-0.2%
Drain burst with terminal fence	406,167 increments/s	1.6% MAD	403,005 increments/s	1.2% MAD	-0.8%
Drain burst with a change observer	382,133 increments/s	0.6% MAD	376,380 increments/s	0.4% MAD	-1.5%
Lookup and send to one child	331,484 increments/s	1.2% MAD	329,677 increments/s	0.4% MAD	-0.5%
Start and stop a machine	118,259 machines/s	1.6% MAD	117,841 machines/s	2.9% MAD	-0.4%
Start and stop a parent with one child	23,976 families/s	1.1% MAD	23,282 families/s	1.1% MAD	-2.9%
Complete an Effect invocation with tracing enabled	7,078 invocations/s	0.5% MAD	7,086 invocations/s	0.6% MAD	+0.1%
Complete an Effect invocation with tracing disabled	8,543 invocations/s	1.3% MAD	8,659 invocations/s	0.7% MAD	+1.4%
Plan transitions through a compound state	102,866 transitions/s	1.8% MAD	104,047 transitions/s	2.0% MAD	+1.1%
Plan transitions through parallel regions	81,229 transitions/s	0.5% MAD	82,084 transitions/s	0.5% MAD	+1.1%
Drain burst through a compound state	347,128 events/s	0.9% MAD	344,930 events/s	0.9% MAD	-0.6%
Drain burst through two parallel regions	318,144 events/s	0.9% MAD	317,580 events/s	0.2% MAD	-0.2%
Drain a compound-state burst with a change observer	325,145 events/s	0.3% MAD	320,324 events/s	0.3% MAD	-1.5%
Idle machine heap per unit	1.9 KiB	1.4% MAD	1.9 KiB	0.3% MAD	+0.0%
Raw generic managed process heap per unit	11.6 KiB	0.2% MAD	11.7 KiB	0.1% MAD	+0.7%
Raw compiled process heap per unit	3.1 KiB	0.0% MAD	3.1 KiB	0.1% MAD	-0.1%
Two independent idle machines heap per unit	3.5 KiB	0.0% MAD	3.5 KiB	0.0% MAD	+0.0%
Idle parent with one child heap per unit	6.0 KiB	0.0% MAD	6.0 KiB	0.0% MAD	0.0%
Parent with observed child registry heap per unit	9.5 KiB	0.0% MAD	9.5 KiB	0.0% MAD	-0.0%
Parent with observed invoked child snapshots heap per unit	6.9 KiB	0.1% MAD	6.9 KiB	0.0% MAD	+0.1%

Process runtime reference change from base

Metric	Base	Base variability	PR	PR variability	Difference
Start and stop a raw generic process	20,366 processes/s	0.9% MAD	19,867 processes/s	3.4% MAD	-2.4%
Start and stop a raw compiled process	67,995 processes/s	1.0% MAD	69,266 processes/s	0.5% MAD	+1.9%

Regression guard

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

Versions and interpretation

• Effect Machine: 0.42.0

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.