Replace transition wrapper with fluent handlers

[SandroMaglione]

Summary

• replace Machine.transition(...) with inline fluent target selectors, target-specific .resolve(...), resolver-free .reenter(), and to.branches(...)
• preserve exact handler, lifecycle, branch, target, decline, topology, visualizer, and MachineTest typing/behavior with compiler and language-service coverage
• remove the definition-bound .invoke(...) method and make Machine.invoke(...) preserve owner and source inference in every handler context
• migrate public docs, examples, fixtures, benchmarks, runtime tests, and typetests to the canonical API

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

Additional local validation: pnpm check passed with 484 runtime tests and 182 typetests; pnpm check also passed in platformer, playground, and pokemon. pnpm perf:types and pnpm perf:runtime completed successfully.

[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)	10,439	10,439	0 (0.0%)
machine.handle (3 states, 2 transitions)	54,695	32,036	-22,659 (-41.4%)
fluent transition (10 named branches)	97,636	119,749	+22,113 (+22.6%)
Machine.invoke (state-dependent Effect)	61,699	93,494	+31,795 (+51.5%)
machine.handle (depth 24)	180,815	205,744	+24,929 (+13.8%)
machine.handle (wide depth 16)	212,025	237,098	+25,073 (+11.8%)
machine.handle (parallel/history/choice)	125,861	141,115	+15,254 (+12.1%)
machine definition (3 independent implementations)	126,173	140,991	+14,818 (+11.7%)
machine exact input/output/error/services	109,419	126,285	+16,866 (+15.4%)
execution adapter readiness	119,676	135,186	+15,510 (+13.0%)

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)	7,392	7,392	0 (0.0%)
machine.handle (3 states, 2 transitions)	44,256	21,597	-22,659 (-51.2%)
fluent transition (10 named branches)	87,707	109,820	+22,113 (+25.2%)
Machine.invoke (state-dependent Effect)	52,853	84,648	+31,795 (+60.2%)
machine.handle (depth 24)	161,125	186,054	+24,929 (+15.5%)
machine.handle (wide depth 16)	193,334	218,407	+25,073 (+13.0%)
machine.handle (parallel/history/choice)	106,185	121,439	+15,254 (+14.4%)
machine definition (3 independent implementations)	110,627	125,445	+14,818 (+13.4%)
machine exact input/output/error/services	95,328	112,194	+16,866 (+17.7%)
execution adapter readiness	56,089	103,709	+47,620 (+84.9%)

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	0.10s
Machine.make (3 states, 2 events)	0.15s	0.16s
machine.handle (3 states, 2 transitions)	0.31s	0.26s
fluent transition (10 named branches)	0.43s	0.53s
Machine.invoke (state-dependent Effect)	0.39s	0.45s
machine.handle (depth 24)	0.68s	0.80s
machine.handle (wide depth 16)	0.70s	0.80s
machine.handle (parallel/history/choice)	0.59s	0.66s
machine definition (3 independent implementations)	0.58s	0.63s
machine exact input/output/error/services	0.54s	0.58s
execution adapter readiness	0.51s	0.60s

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 9V74 80-Core Processor with Node v24.19.0.

Pull request baseline

Scenario	Effect Machine
Plan counter transitions	141,695 transitions/s
Drain burst with terminal fence	409,455 increments/s
Drain burst with a change observer	386,606 increments/s
Lookup and send to one child	352,664 increments/s
Start and stop a machine	176,087 machines/s
Start and stop a parent with one child	51,549 families/s
Plan transitions through a compound state	122,266 transitions/s
Plan transitions through parallel regions	105,549 transitions/s
Drain burst through a compound state	350,364 events/s
Drain burst through two parallel regions	359,912 events/s
Drain a compound-state burst with a change observer	331,080 events/s

Process runtime reference points

Scenario	Effect Machine
Start and stop a raw generic process	34,277 processes/s
Start and stop a raw compiled process	84,617 processes/s

Memory profile	Effect Machine
Idle machine	1.8 KiB
Raw generic managed process	13.9 KiB
Raw compiled process	3.1 KiB
Two independent idle machines	3.4 KiB
Idle parent with one child	5.8 KiB
Parent with observed child registry	10.0 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	142,587 transitions/s	0.3% MAD	141,695 transitions/s	0.7% MAD	-0.6%
Drain burst with terminal fence	416,178 increments/s	0.8% MAD	409,455 increments/s	2.0% MAD	-1.6%
Drain burst with a change observer	392,110 increments/s	0.4% MAD	386,606 increments/s	1.7% MAD	-1.4%
Lookup and send to one child	358,179 increments/s	0.4% MAD	352,664 increments/s	1.2% MAD	-1.5%
Start and stop a machine	176,710 machines/s	1.1% MAD	176,087 machines/s	0.4% MAD	-0.4%
Start and stop a parent with one child	51,682 families/s	1.0% MAD	51,549 families/s	0.7% MAD	-0.3%
Plan transitions through a compound state	123,642 transitions/s	1.1% MAD	122,266 transitions/s	2.8% MAD	-1.1%
Plan transitions through parallel regions	102,395 transitions/s	0.9% MAD	105,549 transitions/s	0.8% MAD	+3.1%
Drain burst through a compound state	344,300 events/s	0.3% MAD	350,364 events/s	1.4% MAD	+1.8%
Drain burst through two parallel regions	355,661 events/s	1.1% MAD	359,912 events/s	1.4% MAD	+1.2%
Drain a compound-state burst with a change observer	328,522 events/s	1.1% MAD	331,080 events/s	1.7% MAD	+0.8%
Idle machine heap per unit	1.8 KiB	0.1% MAD	1.8 KiB	0.2% MAD	+0.2%
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	0.2% MAD	3.1 KiB	0.5% MAD	-0.4%
Two independent idle machines heap per unit	3.4 KiB	0.0% MAD	3.4 KiB	0.0% MAD	+0.5%
Idle parent with one child heap per unit	5.8 KiB	0.0% MAD	5.8 KiB	0.0% MAD	+0.0%
Parent with observed child registry heap per unit	10.0 KiB	0.0% MAD	10.0 KiB	0.0% MAD	+0.0%
Parent with observed invoked child snapshots heap per unit	6.3 KiB	0.0% MAD	6.3 KiB	0.0% MAD	+0.0%

Process runtime reference change from base

Metric	Base	Base variability	PR	PR variability	Difference
Start and stop a raw generic process	34,491 processes/s	1.0% MAD	34,277 processes/s	1.2% MAD	-0.6%
Start and stop a raw compiled process	83,486 processes/s	0.3% MAD	84,617 processes/s	1.7% MAD	+1.4%

Regression guard

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

Versions and interpretation

• Effect Machine: 0.16.0

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.