[SandroMaglione]

Summary

• Bridge atoms built a new server value on every server read, so React warned during hydration that "The result of getServerSnapshot should be cached to avoid an infinite loop", including through MachineState.
• Each bridge atom's server value is now memoized on the identity of its inputs: the bridge plan for snapshot and child snapshot, and the source server values for result, child result, selectors (select*, matches*), can, and family projections. Repeated reads, including reads from different registries, return the same reference. Derived atoms stay stable because their sources are.
• useRetainedResult in @typeonce/effect-machine-react computes its server snapshot once per store.
• Tests: a server-value stability test covering bridge, child, selector, can, family and familyChild atoms, and a hydration assertion that React logs no getServerSnapshot warning. Both fail on main.

Changeset

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

Patch for @typeonce/effect-machine and @typeonce/effect-machine-react.

Validation

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

Local pnpm check notes: dprint plugin downloads are blocked in the local sandbox, so formatting was checked with the same plugin versions loaded from npm. packages/devtools/test/StaticSite.test.ts times out locally on main as well; CI is authoritative. pnpm perf:runtime ran successfully as a smoke test.

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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	0.03s	0.03s
Import effect-machine	0.03s	0.03s
Machine.state (3 children)	0.09s	0.09s
Machine.make (3 states, 2 events)	0.14s	0.15s
machine.handle (3 states, 2 transitions)	0.31s	0.34s
declared transition (10 named branches)	0.38s	0.40s
atomic construction, guards, and reentry	0.52s	0.58s
registered invocation (input-taking Effect)	0.31s	0.32s
machine.handle (depth 24)	0.64s	0.66s
machine.handle (wide depth 16)	0.73s	0.73s
machine.handle (parallel/history/choice)	0.54s	0.54s
machine definition (3 independent implementations)	0.55s	0.55s
machine exact input/output/error/services	0.53s	0.51s
execution adapter readiness	0.47s	0.45s

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 INTEL(R) XEON(R) PLATINUM 8573C with Node v24.21.0.

Pull request baseline

Scenario	Effect Machine
Plan counter transitions	135,435 transitions/s
Drain burst with terminal fence	464,008 increments/s
Drain burst with a change observer	438,540 increments/s
Lookup and send to one child	400,072 increments/s
Start and stop a machine	147,951 machines/s
Start and stop a parent with one child	42,695 families/s
Complete an Effect invocation with tracing enabled	16,835 invocations/s
Complete an Effect invocation with tracing disabled	20,493 invocations/s
Plan transitions through a compound state	121,952 transitions/s
Plan transitions through parallel regions	97,188 transitions/s
Drain burst through a compound state	378,160 events/s
Drain burst through two parallel regions	341,647 events/s
Drain a compound-state burst with a change observer	359,364 events/s

Process runtime reference points

Scenario	Effect Machine
Start and stop a raw generic process	35,102 processes/s
Start and stop a raw compiled process	84,381 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	134,678 transitions/s	1.3% MAD	135,435 transitions/s	0.3% MAD	+0.6%
Drain burst with terminal fence	466,286 increments/s	1.4% MAD	464,008 increments/s	1.0% MAD	-0.5%
Drain burst with a change observer	441,794 increments/s	1.3% MAD	438,540 increments/s	0.6% MAD	-0.7%
Lookup and send to one child	407,093 increments/s	0.5% MAD	400,072 increments/s	1.0% MAD	-1.7%
Start and stop a machine	147,210 machines/s	1.0% MAD	147,951 machines/s	0.9% MAD	+0.5%
Start and stop a parent with one child	42,305 families/s	0.8% MAD	42,695 families/s	2.5% MAD	+0.9%
Complete an Effect invocation with tracing enabled	17,085 invocations/s	0.5% MAD	16,835 invocations/s	0.9% MAD	-1.5%
Complete an Effect invocation with tracing disabled	20,536 invocations/s	0.1% MAD	20,493 invocations/s	0.9% MAD	-0.2%
Plan transitions through a compound state	120,607 transitions/s	0.5% MAD	121,952 transitions/s	0.1% MAD	+1.1%
Plan transitions through parallel regions	96,414 transitions/s	0.5% MAD	97,188 transitions/s	0.5% MAD	+0.8%
Drain burst through a compound state	381,602 events/s	2.1% MAD	378,160 events/s	3.2% MAD	-0.9%
Drain burst through two parallel regions	348,352 events/s	3.7% MAD	341,647 events/s	2.3% MAD	-1.9%
Drain a compound-state burst with a change observer	360,803 events/s	2.2% MAD	359,364 events/s	2.0% MAD	-0.4%
Idle machine heap per unit	1.9 KiB	0.3% MAD	1.9 KiB	0.6% MAD	+0.7%
Raw generic managed process heap per unit	11.7 KiB	0.0% MAD	11.7 KiB	0.0% MAD	+0.1%
Raw compiled process heap per unit	3.1 KiB	0.1% MAD	3.1 KiB	1.1% MAD	+1.0%
Two independent idle machines heap per unit	3.5 KiB	0.1% MAD	3.5 KiB	0.1% MAD	+0.1%
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	-0.1%
Parent with observed invoked child snapshots heap per unit	6.9 KiB	0.0% MAD	6.9 KiB	0.2% MAD	+0.1%

Process runtime reference change from base

Metric	Base	Base variability	PR	PR variability	Difference
Start and stop a raw generic process	34,789 processes/s	0.6% MAD	35,102 processes/s	0.6% MAD	+0.9%
Start and stop a raw compiled process	84,005 processes/s	0.2% MAD	84,381 processes/s	1.4% MAD	+0.4%

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.