Continuum (Phase VI)

Continuum moves beyond value/state PIR exchange toward suspended computation migration:

pause → capture continuation → Universal Execution State → translate → resume

This chapter describes what is implemented today versus what remains experimental or unsupported.

PIR vs UES vs PCIR

Artifact	Models	Version constant
PIR	Portable values / object graphs	`pir_schema`
UES	Suspended execution (control, frames, heap, capabilities)	`ues_format`
PCIR	Portable control-flow subset for supported regions	`pcir_schema`

These versions advance independently (see Versioning). Serialization alone is not migration.

What is real in this milestone

Types + serde for UniversalExecutionState, UniversalFrame, PCIR ops, binary/JSON envelopes, version rejection.
Safepoint model with machine-readable reports (can_capture / snapshot / replay / migrate, targets, semantic loss).
Explicit checkpoint capture in Python and JavaScript workers via parallax.checkpoint(label) (and @parallax.safepoint / parallax.safepoint conceptually).
Same-runtime resume of the post-checkpoint source region with restored bindings (not a full program restart).
MigrationContract analysis before continuation attempts; clear reject reports when unsatisfied.
Continuation capability matrix via CLI.

What is Explicitly Unsupported / Experimental

Capability	Status
Arbitrary live stack frame migration	NO — not claimed
Cross-runtime continuation resume	NO (contract-gated)
Deterministic replay engine	UNSUPPORTED (journal schema / hooks only)
Async / await / yield migration	NO
WASM continuum	NO
Same-runtime checkpoint capture + resume	EXPERIMENTAL

If a path is not truly implemented, Continuum returns structured Unsupported / capability levels (YES / PARTIAL / EXPERIMENTAL / NO) — it never pretends resume worked.

Safepoints

Supported boundary for this pass: explicit checkpoint.

x = 1
parallax.checkpoint("after_init")
x = x + 41  # runs only on resume

At the safepoint the worker reports whether it can capture / snapshot / replay / migrate, candidate targets, and semantic-loss notes.

CLI

# Continuation capability matrix
plx capabilities python --continuations
plx capabilities --continuations --json

# Capture UES at checkpoint (experimental)
plx continuum examples/checkpoint_demo.py -o demo.ues.json --json

# Same-runtime resume after capture
plx continuum examples/checkpoint_demo.py --resume --json

# Inspect a written UES
plx continuum demo.ues.json --inspect-ues

# Contract-only analysis
plx continuum examples/checkpoint_demo.py --analyze-only -t javascript

# Honest continuation migrate mode (rejects cross-runtime)
plx migrate examples/checkpoint_demo.py -t javascript --mode continuation

Value/state PIR migration remains the default:

plx migrate examples/demo.py -t javascript

Before a live continuation attempt, Parallax builds a MigrationContract describing required surviving semantics (values, locals, control position, stack frames, same-runtime vs cross-runtime resume, …). Analysis runs first; unsatisfied contracts produce a readable reject report.

Crates

parallax-pcir — Continuation IR ops / programs
parallax-ues — UES, frames, safepoints, deterministic hooks, continuation matrix
parallax-migrate::contract — MigrationContract + analysis

Parallax Documentation