Add explicit targetless transitions

[SandroMaglione]

Summary

• add target.none() as the explicit handled-without-destination result for event, lifecycle, and invocation transitions
• allow target.none() regardless of declared concrete targets, including targetless reentry, in both generic and optimized planners
• remove Machine.retag and migrate callers to discriminator destructuring plus target .from(...)
• update README, agent guide, JSDocs, examples, fixtures, benchmarks, runtime tests, and type tests

Changeset

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

Added a minor changeset for the pre-1.0 package.

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

Validated pnpm check, pnpm check in pokemon, playground, and platformer, pnpm perf:types, and pnpm perf:runtime locally. The PR performance workflows remain authoritative for base-versus-PR comparisons.

[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)	3,039	3,039	0 (0.0%)
Machine.make (3 states, 2 events)	13,199	13,199	0 (0.0%)
machine.handle (3 states, 2 transitions)	30,310	30,391	+81 (+0.3%)
Machine.invoke (state-dependent Effect)	70,064	70,267	+203 (+0.3%)
machine.handle (depth 24)	187,523	187,535	+12 (+0.0%)
machine.handle (wide depth 16)	219,925	219,937	+12 (+0.0%)
machine.handle (parallel/history/choice)	127,412	127,424	+12 (+0.0%)
machine.handle (4 successive calls)	135,030	135,105	+75 (+0.1%)
machine exact input/output/error/services	109,263	109,347	+84 (+0.1%)
execution adapter readiness	121,040	121,052	+12 (+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)	2,984	2,984	0 (0.0%)
Machine.make (3 states, 2 events)	10,152	10,152	0 (0.0%)
machine.handle (3 states, 2 transitions)	17,111	17,192	+81 (+0.5%)
Machine.invoke (state-dependent Effect)	59,031	59,234	+203 (+0.3%)
machine.handle (depth 24)	167,454	167,466	+12 (+0.0%)
machine.handle (wide depth 16)	200,917	200,929	+12 (+0.0%)
machine.handle (parallel/history/choice)	101,758	101,770	+12 (+0.0%)
machine.handle (4 successive calls)	113,779	113,854	+75 (+0.1%)
machine exact input/output/error/services	92,732	92,816	+84 (+0.1%)
execution adapter readiness	86,962	86,974	+12 (+0.0%)

Check times (informational)

Scenario	Base	PR
Effect only	0.03s	0.02s
Import effect-machine	0.03s	0.02s
Machine.defineStates (3 states)	0.09s	0.08s
Machine.make (3 states, 2 events)	0.14s	0.14s
machine.handle (3 states, 2 transitions)	0.22s	0.23s
Machine.invoke (state-dependent Effect)	0.32s	0.33s
machine.handle (depth 24)	0.57s	0.57s
machine.handle (wide depth 16)	0.58s	0.60s
machine.handle (parallel/history/choice)	0.46s	0.47s
machine.handle (4 successive calls)	0.47s	0.49s
machine exact input/output/error/services	0.43s	0.44s
execution adapter readiness	0.44s	0.44s

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	119,943 transitions/s
Drain burst with terminal fence	375,858 increments/s
Drain burst with a change observer	350,864 increments/s
Lookup and send to one child	317,364 increments/s
Start and stop a machine	150,150 machines/s
Start and stop a parent with one child	42,042 families/s
Plan transitions through a compound state	107,917 transitions/s
Plan transitions through parallel regions	87,504 transitions/s
Drain burst through a compound state	341,513 events/s
Drain burst through two parallel regions	323,790 events/s
Drain a compound-state burst with a change observer	322,441 events/s

Process runtime reference points

Scenario	Effect Machine
Start and stop a raw generic process	27,009 processes/s
Start and stop a raw compiled process	67,417 processes/s

Memory profile	Effect Machine
Idle machine	1.7 KiB
Raw generic managed process	13.6 KiB
Raw compiled process	2.9 KiB
Two independent idle machines	3.3 KiB
Idle parent with one child	5.2 KiB
Parent with observed child registry	9.4 KiB
Parent with observed invoked child snapshots	5.6 KiB

Effect Machine change from base

Metric	Base	Base variability	PR	PR variability	Difference
Plan counter transitions	117,860 transitions/s	1.0% MAD	119,943 transitions/s	1.0% MAD	+1.8%
Drain burst with terminal fence	372,871 increments/s	1.9% MAD	375,858 increments/s	0.4% MAD	+0.8%
Drain burst with a change observer	352,012 increments/s	1.9% MAD	350,864 increments/s	0.2% MAD	-0.3%
Lookup and send to one child	320,460 increments/s	2.5% MAD	317,364 increments/s	0.3% MAD	-1.0%
Start and stop a machine	150,150 machines/s	1.3% MAD	150,150 machines/s	0.9% MAD	0.0%
Start and stop a parent with one child	42,490 families/s	0.9% MAD	42,042 families/s	1.3% MAD	-1.1%
Plan transitions through a compound state	107,105 transitions/s	1.0% MAD	107,917 transitions/s	1.0% MAD	+0.8%
Plan transitions through parallel regions	86,345 transitions/s	2.0% MAD	87,504 transitions/s	0.6% MAD	+1.3%
Drain burst through a compound state	342,977 events/s	1.3% MAD	341,513 events/s	0.7% MAD	-0.4%
Drain burst through two parallel regions	322,418 events/s	1.1% MAD	323,790 events/s	1.0% MAD	+0.4%
Drain a compound-state burst with a change observer	323,824 events/s	1.1% MAD	322,441 events/s	0.1% MAD	-0.4%
Idle machine heap per unit	1.7 KiB	0.3% MAD	1.7 KiB	0.3% MAD	-0.2%
Raw generic managed process heap per unit	13.6 KiB	0.0% MAD	13.6 KiB	0.0% MAD	-0.0%
Raw compiled process heap per unit	2.9 KiB	0.2% MAD	2.9 KiB	0.2% MAD	+0.2%
Two independent idle machines heap per unit	3.3 KiB	0.0% MAD	3.3 KiB	0.0% MAD	+0.0%
Idle parent with one child heap per unit	5.2 KiB	0.0% MAD	5.2 KiB	0.0% MAD	0.0%
Parent with observed child registry heap per unit	9.4 KiB	0.0% MAD	9.4 KiB	0.0% MAD	+0.0%
Parent with observed invoked child snapshots heap per unit	5.6 KiB	0.2% MAD	5.6 KiB	0.1% MAD	+0.4%

Process runtime reference change from base

Metric	Base	Base variability	PR	PR variability	Difference
Start and stop a raw generic process	26,325 processes/s	3.3% MAD	27,009 processes/s	1.3% MAD	+2.6%
Start and stop a raw compiled process	66,876 processes/s	0.7% MAD	67,417 processes/s	1.0% MAD	+0.8%

Regression guard

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

Versions and interpretation

• Effect Machine: 0.9.0

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.