[Tielem]

Two breaking, mechanical changes from plans/in-progress/syntax-foundations.md, riding the unreleased 0.20.0. Neither adds behaviour; both exist so that the features that need them (suspend, endpoints) can be purely additive.

1. A rule is an effect and an exit

emit used to be two things at once: append a value, and go to activity X, which it carried inside itself as a required transition. That reads fine in onSuccess and nowhere else — a rule that runs while an activity is live has nowhere to continue to, so every such list would need a second, transition-less spelling of the same word.

Every rule, in every list, is now:

• an optional condition;
• at most one effect — emit, workflow.call;
• at most one exit — transition, result, error.

# Before                              # After
- emit:                               - emit: { messages: "{{ output.messages }}" }
    value: { messages: "…" }            transition: { name: wait }
    transition: { name: wait }

The lists differ only in whether an exit is required: onSuccess and onFailure end the activity, so the run must go somewhere; an onEmitted rule runs once per value, and there an exit is what stops consuming.

• handle becomes workflow.call. It does what the workflow.call activity does, so it takes that name, and the dotted key resolves through the effect oneof exactly as type: workflow.call resolves through config. Named for what it dispatches, since workspace.exec is already proposed and a bare call: would stop reading.
• EmissionRule collapses into TransitionRule. One rule type, not two.
• emit is allowed in onEmitted, which is what a filtering consumer needs — republish only the invoices, without a document whose only job is to republish a value.
• At most one effect, enforced by the oneof, since two would need an order the document cannot express.
• A rule with neither an effect nor an exit is UTOS-T001.

2. Durations are strings

timeout: 24h was never expressible: the source format ends by reading the document as proto3 JSON, where a duration is spelled only in seconds. The timer's own examples used 30s, which is why nobody noticed.

A duration is now a string in the unit shorthand that Kubernetes, Argo, Prometheus and Docker Compose use — 90s, 8h, 1h30m, 3d — whole numbers, largest unit first, no fractions and no ISO 8601. 86400s stays valid, so every timer written today keeps working.

It may also be a whole-field template, so a reusable document can let its caller choose how long it waits, and a backoff can finally honour a Retry-After header. The rendered value and the instant it resolves to are recorded when the activity is entered, so a replay reads the same deadline. duration joins the type registry as utos:duration.

Codes

• reworded: UTOS-T001 (at most one effect, at most one exit, not neither), UTOS-C202 (a literal duration is positive)
• new: UTOS-C203 (a literal duration's syntax), UTOS-E106 (what a duration template renders to)
• retired: UTOS-T004, UTOS-C504

Decisions worth a look

1. No spawn effect yet. The plan's proto sketch lists it, but it comes from spawn-action.md, still in preparing/, and it would be new behaviour. DispatchEffect has call only and field 2 is left free, so adding it later is additive.
2. emit and result stay google.protobuf.Struct, not WorkflowMap — the one place this departs from the plan's sketch. A bundle holds templates, never values, and no template can contain a blob. The blob case this raises (an endpoint receiving a binary PUT) works through the template rendering to a value at run time; the two notes it does need are recorded in suspend.md.
3. No "two exits" fixture, which the plan's verification list asks for: two members of one oneof cannot survive proto3 JSON parsing, so a validator never sees it.

Breaking

TransitionRule's action oneof is replaced by effect and exit; EmitAction and EmissionRule are gone; CallActivityConfig.on_emitted and TimerActivityConfig.duration take new field numbers, with the old ones reserved. buf breaking reports exactly these and nothing else.

Migration tables are in workflow-source-format.md § Migrating.

Checks

• buf lint clean; buf breaking shows only the intended changes.
• Six fixtures migrated to the new shape; new fixtures for the rule shapes, both duration codes, the dotted effect key and two effects in one rule. The evaluation corpus gains a duration form.
• Every fixture parses, every link resolves, and the new expressions are syntax-checked.

sdk-dotnet, the daemon, the CLI and workflows/ follow; the plan tracks them.