feat(intent): a create-from on the process-step axis, and an opt-in append cardinality (#6800)

[delchev]

Closes #6800.

What was missing

"On event E, append a derived row" — a LogEntry per process step, a protocol line per status change — had no expression. Every candidate answers a different question: postings/posts are idempotent per source, rollups/aggregates recompute an existing row and never insert, and an event-driven generates create-from is at-most-once by construction. What was left was a hand-written listener under custom/, or an outbound → inbound loopback whose only purpose was to defeat that guard.

Separately, a create-from bound only to the source's own lifecycle, while notifications, integrations and departures bind to the lifecycle or a process step — so a follow-up document belonging to a moment in a flow had no trigger to hang off.

The two additions

generates:
  - name: log-activation
    from: Claim
    to: LogEntry
    event: { onStepCompleted: { process: ClaimApproval, step: activate }, mode: append }
    map:
      Claim: id                # back-reference: REQUIRED in both modes
      amount: amount
    defaults:
      step: "activate"
      date: now

1. The step axis — onStepReached / onStepCompleted: { process, step }, narrowed by one rule of its own: the process's trigger: entity must be the from: entity, because the step event is delivered as a message about the record its process runs on and that record is what the create-from reads by id. The step must be a user/service task; a fromUses: source is rejected (a process and its steps belong to the model that declares them); when: stays optional — the step is the moment.
2. mode: — once (default, unchanged) or append, which drops the existing-target lookup so every delivery creates a row.

The back-reference stays required in both cardinalities: the dedup key under once, the created row's provenance under append.

Two things worth reviewing

• StepEventSupport.boundEvents had to learn about generates, not just the glue builder. emitters() reads that list, so a moment whose only consumer is a create-from would otherwise get no JavaDelegate emitter and the listener would bind a topic nothing publishes to.
• GlueGenerator (ide-template) binds an explicit key allow-list into the Velocity context. An unbound key renders as its own literal — which is exactly how the listener's destination() silently lost its suffix on the first run here (…-Slip${topicSuffix}), caught by the existing IntentEmissionCoverageIT assertion.

What append is not

The absence of a guard, not a state-aware one. Delivery is at-least-once (the step topic is published after commit, not transactionally with the step — the contract outbound already states), so a redelivery appends a duplicate row. It is not the answer to "I voided the document and cannot regenerate it" — that needs #6814's stage-aware predicate on mode: once. And two append rules sharing a target and a back-reference are legal by design (each records a different moment), which is why #6813's parse-time collision diagnostic must be scoped to once pairs only. Both are stated in the template javadoc, the assistant guide and the module CLAUDE.md.

Tests

• GeneratesIntentTest — the step binding parses; unknown process / unknown step / non-eventable kind / trigger-entity mismatch / cross-model source / a mode with no trigger / an unknown mode / a missing back-reference under append / a prompt on an appending create-from all rejected with named messages; the default cardinality is once.
• GlueGeneratesTest — the step-scoped topic, appendMode dropping the lookup, the emitter for a generates-only moment, and both lifecycle axes plus the click-only form unchanged.
• IntentEmissionCoverageIT — emission tokens, and the runtime: one shipment whose all-serviceTask flow appends two log rows from two moments sharing the same back-reference, a click on the kept button appending a third, and the at-most-once sibling on the same moment minting exactly one summary that a later click hands back. Passes headless (-Dit.test=IntentEmissionCoverageIT).
• mvn formatter:validate clean, engine-intent 703 + ide-template 77 unit tests green, javadoc clean under -P release.

Docs

• in-repo: intent-assistant-guide.md + engine-intent/CLAUDE.md (this PR).
• dirigible.io: docs(intent): the create-from's step axis and mode: once|append dirigible-io/dirigible-io.github.io#199 (merged).
• intentfile.org spec: spec: a create-from on the process-step axis, and an opt-in append cardinality IntentFile/intent-specification#39 (proposal 0021) and docs: the create-from's step axis and its append cardinality IntentFile/intentfile.github.io#30, both left open for the maintainer.