feat(workflows): opt-in output_format: json exposes parsed shell stdout as output.data (#2963)

* feat(workflows): opt-in output_format: json exposes parsed shell stdout as output.data

No step that runs external code could hand a typed value to a later
step, so e.g. a fan-out could never consume a runtime-computed
collection. With output_format: json declared, stdout is parsed and
exposed under output.data (raw keys unchanged); a parse failure fails
the step with a clear error. Without the key, behavior is unchanged.

Reference implementation for the proposal in #2962.

Addresses #2962

* test(shell): emit JSON via sys.executable for cross-platform output_format tests

Address review (#2963): replace non-portable echo '{...}' (Windows cmd.exe keeps the single quotes, breaking JSON) with the established '"{py}" "{script}"' pattern using sys.executable + a temp script, so the output_format tests pass on the Windows CI matrix. Also make the validate test's run inert (exit 0).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

src/specify_cli/workflows/steps/shell/__init__.py

@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 
+import json
 import subprocess
 from typing import Any
 
@@ -49,6 +50,23 @@ class ShellStep(StepBase):
                     error=f"Shell command exited with code {proc.returncode}.",
                     output=output,
                 )
+            if config.get("output_format") == "json":
+                # Opt-in structured output: expose the parsed stdout under
+                # ``output.data`` so later steps can consume typed values
+                # (e.g. a fan-out's ``items:``). A parse failure fails the
+                # step — declaring ``output_format: json`` is a contract.
+                try:
+                    output["data"] = json.loads(proc.stdout)
+                except json.JSONDecodeError as exc:
+                    return StepResult(
+                        status=StepStatus.FAILED,
+                        error=(
+                            f"Shell step {config.get('id', '?')!r} declared "
+                            f"output_format: json but stdout is not valid "
+                            f"JSON: {exc}"
+                        ),
+                        output=output,
+                    )
             return StepResult(
                 status=StepStatus.COMPLETED,
                 output=output,
@@ -72,4 +90,10 @@ class ShellStep(StepBase):
             errors.append(
                 f"Shell step {config.get('id', '?')!r} is missing 'run' field."
             )
+        output_format = config.get("output_format")
+        if output_format is not None and output_format != "json":
+            errors.append(
+                f"Shell step {config.get('id', '?')!r}: 'output_format' must "
+                f"be 'json' when present, got {output_format!r}."
+            )
         return errors