process-gap(per-story-delivery): step (f) silently degrades from 9-step pr-manager process to self-review when subagent spawning is unavailable

## Summary

Per-story-delivery step (f) specifies a 9-step pr-manager process that includes dispatching a fresh pr-reviewer subagent for the final fresh-eyes review. In harnesses where a delegated pr-manager agent **cannot itself spawn subagents** (a common restriction: teammates/subagents may not spawn further subagents), the step **silently degrades to self-review** — the pr-manager performs the "pr-reviewer pass" itself and reports the step complete. No failure signal reaches the orchestrator.

## Why it matters

The pr-reviewer's entire value is the information-asymmetry guarantee: a reviewer that has NOT seen the implementation context, seeing only diff + description + CI evidence, finds a different class of issues than the agent that assembled the PR. A self-review by the PR's own author-coordinator does not satisfy that guarantee, however diligent.

Direct evidence of signal loss from our cycle: the pr-manager's self-conducted review passes returned zero findings; an orchestrator-dispatched independent fresh reviewer (restricted to diff + description + CI only) subsequently found **two confirmed description-accuracy defects** the self-review had missed — both verified against ground truth and fixed before merge-ready was declared.

## Observable symptoms

- Step (f) reports complete without a distinct pr-reviewer agent trace in the session.
- The pr-manager's report phrases the review as conducted "directly" (often with an explicit note that it cannot spawn subagents).

## Suggested improvements

1. Step (f) should declare subagent-spawn capability as an explicit precondition, checked at dispatch time.
2. When the capability is absent, the workflow should mandate the fallback rather than leave it to improvisation: pr-manager reports the degradation as a distinct status, and the ORCHESTRATOR dispatches the pr-reviewer directly (it holds context, but the reviewer prompt can enforce the restricted input surface: diff + description + CI evidence only, no repo/spec reads).
3. The pr-reviewer agent definition already encodes the restricted-view contract; the per-story-delivery text should reference it as the non-negotiable property of the step, so "review happened" is never accepted as equivalent to "information-asymmetric review happened."

Examine the per-story-delivery workflow definition, likely in a workflow or orchestration module. Look for step (f) and the pr-manager agent's dispatch logic. Identify where subagent spawning is attempted and the capability check is missing. Review the pr-reviewer agent's prompt to understand the restricted input contract. The fix involves adding a precondition check and a fallback path where the orchestrator directly dispatches the reviewer.

Written by the indexing model from the issue text.