Recipe engine records a failed step as completed with empty output, corrupting resume

Environment

• amplifier 2026.07.13-51194ef
• core 1.6.0
• Linux (WSL2)

Component

amplifier-bundle-recipes / recipe engine

Problem

During a long multi-step recipe run, a step's agent sub-session died mid-turn. In one instance, the provider raised NotFoundError; in another, the model emitted a thinking-only response and the session ended with empty output. The engine recorded the step in the session's state.json as COMPLETED with empty output rather than failed.

Impact

• operation=resume skips the step
• Downstream steps receive an empty string for its declared output
• The run continues silently corrupted
• Workaround: hand-editing the recipe session's state.json (remove the phantom completed step, rewind current_step_index), then resuming
• This is required after every such failure

Expected Behavior

A step whose sub-session errors — or returns empty output when the step declares an output — should be recorded as failed/retryable and re-run on resume, never completed.

Related Observation

Recipe session state was stored under a literal unexpanded placeholder directory with a doubled segment: ~/.amplifier/projects/{project}/recipe-sessions/<project-slug>/recipe-sessions/<session-id>/ — worth checking while in this area.

Start in the amplifier-bundle-recipes recipe engine's step-state handling and reproduce a failed or empty-output sub-session in a multi-step recipe. Inspect the session state.json and resume behavior, including the reported session-path placeholder. Done means failed or empty-output steps are retryable and resume does not skip them or pass empty output downstream.