awf v0.2.0

New workflow-format capabilities for typed-output artifacts, conditional-branch
optionality, and nested output addressing. Backward-compatible — existing
workflows are unaffected and the workflow-format version (version: 1) is
unchanged.

Added

• output_artifact: on containerless agent steps. A containerless awf/llm
  step can declare output_artifact: <name> to publish its validated
  output_schema object as a first-class, content-addressed artifact
  step.<id>.files.<name>. The dispatcher serializes the typed output to
  canonical JSON (byte-identical to the step's own typed-output blob — one blob,
  two references), so it flows through the existing artifact machinery: a
  deterministic gate evaluator reads it via input_files, and it forwards out of
  a gate to a workflow-level output_files: alias. Validated by AWF3014
  (containerless-only; requires output_schema; mutually exclusive with
  output_files). react is excluded in this release.
• if-branch optionality. A reference from outside an if to a step whose
  branch was not taken now resolves to a distinct ABSENT sentinel (AWF4006)
  instead of failing the run. In outputs: — and symmetrically in a workflow
  output_files: alias — the bound key is simply omitted; a required
output_schema field still fails on omission. Omission composes across a
  sub-workflow call: a child that omits an optional output makes the parent's
  binding omit too. Referencing an absent step anywhere else (a run:
  substitution, a gate until, another step's input) remains an author error.
• first_of: output selection. A workflow output may bind
  first_of: [ <ref>, <ref>, ... ] to select the first present (non-absent)
  reference — the "read whichever if branch ran" pattern — as a structured
  directive, without adding an operator to the templating language.
• awf outputs --step reads nested runtime paths. --step now accepts a
  step's full runtime address verbatim (e.g.
  gate[0].attempt-2.generate.<id>, map[0].item-3.<id>,
  loop[0].body.iter-3.<id>), honoring the documented promise. The caller names
  the instance; a path that names no committed step (including a step under a
  non-taken if branch, or a path missing its suffix) is a read failure
  (exit 1), not a usage error.

Changed

• AWF3012 warning wording. The conditional-scope-output validation warning
  now describes the new omit / required-fail semantics — an output bound to a
  non-taken if branch is omitted (and only required schema fields then fail),
  rather than claiming awf outputs will error.