feat(review): walkthrough/risk_verdict/test_coverage schema

.opencode/agents/pragent.md

@@ -160,6 +160,12 @@ containing STRICT JSON, nothing else after it:
   "risks": [
     "Bullets detailing potential bugs, edge cases, lifecycle issues, or performance risks found across the diff"
   ],
+  "walkthrough": [
+    "a.py: adds X — short plain-prose bullet, file- or change-grouped",
+    "b.py: refactors Y"
+  ],
+  "risk_verdict": "Low|Medium|High|Critical risk: <one-line concrete reason>",
+  "test_coverage": "Tests added" | "Tests changed" | "No tests for behavioral change" | "No test files in repo",
   "findings": [
     {
       "severity": "critical|high|medium|low|info|nit",
@@ -178,6 +184,16 @@ Rules:
 - `summary_changes` (2–4 bullets) goes into the **Summary of Changes** section.
   `risks` (bullets) goes into **Key Risks & Concerns**. Both are required;
   empty arrays are fine when nothing applies.
+- `walkthrough` (2–6 bullets, file- or change-grouped) is the **Walkthrough**
+  section: what the PR does, where, in plain prose. Default to `[]` for a
+  trivial diff. Backward compatible — parsers default to `[]` if absent.
+- `risk_verdict` (exactly one line) goes into the **Risk Verdict** section.
+  Lead with `Low|Medium|High|Critical risk:` followed by a concrete reason.
+  Default to `""` when not applicable. Backward compatible.
+- `test_coverage` (short string) goes into the **Test Coverage** section.
+  Use exactly one of `"Tests added"`, `"Tests changed"`,
+  `"No tests for behavioral change"`, `"No test files in repo"`. Default to `""`.
+  Backward compatible.
 - `suggestion` is the literal new code that replaces the flagged line(s). Minimal —
   just the changed lines, indented as they'd appear in the file. Empty string `""`
   when no safe textual replacement exists (e.g. missing test, architectural note).