Let routed CI cache researched reviews too, from one shared policy

#71 removed the offline index and dropped the research gate from `cacheAllowed`
— but only from runLegacyCi. runRoutedCi, which handles every repo that has
adopted routing.jsonc, kept `!rootConfig.research.enabled` and so has been
running a fresh review for every researched PR, for a reason that stopped
existing when the index did. Both gates were added by the same commit (#61) for
the same index reason, so this was a missed half, not a separate constraint.

Caught by the reviewer on the roadmap PR (#72), which claimed the fix had already
landed. Rather than qualify that claim, make it true.

The duplication is the actual defect: one policy written out twice will drift,
and did. `reviewCacheAllowed` in review-cache.ts is now the single definition and
both paths call it, with a unit test pinning each flag and recording that research
is deliberately not among them.

src/__tests__/review-cache.test.ts

@@ -4,7 +4,12 @@ import { tmpdir } from "node:os";
 import path from "node:path";
 
 import type { LoadedConfig } from "../config/schema.js";
-import { reviewCanBeReused, reviewInputHash, reviewMatchesInput } from "../core/review-cache.js";
+import {
+  reviewCacheAllowed,
+  reviewCanBeReused,
+  reviewInputHash,
+  reviewMatchesInput,
+} from "../core/review-cache.js";
 import type { CoordinatorOutput, DiffEntry } from "../core/schema.js";
 
 const config = (over: Partial<LoadedConfig> = {}): LoadedConfig => ({
@@ -171,3 +176,25 @@ test("file hashing refuses traversal and never follows a PR-controlled symlink",
     await rm(outside, { force: true });
   }
 });
+
+test("reviewCacheAllowed is the one policy both CI paths share", () => {
+  const base = {
+    bypassTriggerGate: false,
+    stack: false,
+    feedback: false,
+    hasMetadata: true,
+  };
+  expect(reviewCacheAllowed(base)).toBe(true);
+
+  // Each flag independently means "this run has an input the key can't represent".
+  expect(reviewCacheAllowed({ ...base, bypassTriggerGate: true })).toBe(false);
+  expect(reviewCacheAllowed({ ...base, stack: true })).toBe(false);
+  expect(reviewCacheAllowed({ ...base, feedback: true })).toBe(false);
+  expect(reviewCacheAllowed({ ...base, hasMetadata: false })).toBe(false);
+
+  // Research is deliberately NOT a gate. It was one only because the offline index
+  // was an artifact the key could not represent; with the index gone, a researched
+  // review fetches everything live during the run. The routed path kept this gate
+  // after the legacy path dropped it, which is the drift this function prevents.
+  expect(reviewCacheAllowed(base)).toBe(true);
+});

src/commands/ci.ts

@@ -30,7 +30,12 @@ import { summarizePriorReview } from "../core/prior-review.js";
 import { dropStaleVerdict, feedbackApplied, feedbackNeedsRunSeam } from "../core/adjudicate.js";
 import { runReview } from "../core/review.js";
 import type { ReviewRunOptions, ReviewRunResult } from "../core/review.js";
-import { reviewCanBeReused, reviewInputHash, reviewMatchesInput } from "../core/review-cache.js";
+import {
+  reviewCacheAllowed,
+  reviewCanBeReused,
+  reviewInputHash,
+  reviewMatchesInput,
+} from "../core/review-cache.js";
 import { GitHubPRSource } from "../sources/github-pr.js";
 import { memoizeSource, stackConfirmFromConfig, stackWalkFromConfig } from "../sources/source.js";
 import type { PreparedReadRoot, ReviewSource, StackWalkOptions } from "../sources/source.js";
@@ -576,13 +581,12 @@ async function runLegacyCi(
   const stack = resolveStackWalk(config.stack, noStackAware);
   const stackConfirm = resolveStackConfirm(config.stack, noStackAware);
   const feedback = adjudicationSeam(config, reporter);
-  // Dynamic stack context and model-backed reply adjudication have inputs outside
-  // the scoped diff. Keep those paths fresh until their inputs join the cache key.
-  // A maintainer's explicit /review is also always a real rerun.
-  // Research no longer forces a fresh run: with the local index gone, every result
-  // is fetched live from an allowlisted host during the run, so there is no mounted
-  // artifact whose contents could drift out from under the cache key.
-  const cacheAllowed = !bypassTriggerGate && !stack && !feedback && metadata !== undefined;
+  const cacheAllowed = reviewCacheAllowed({
+    bypassTriggerGate,
+    stack: Boolean(stack),
+    feedback: Boolean(feedback),
+    hasMetadata: metadata !== undefined,
+  });
   let inputHash: string | undefined;
 
   // The previous review's embedded comment state, read ONCE: the cache check below
@@ -905,12 +909,12 @@ async function runRoutedCi(
     reporterFor(scopedCommentTag(rootTag, name), true),
   );
 
-  const cacheAllowed =
-    !bypassTriggerGate &&
-    !stackWalk &&
-    !feedbackNeedsRunSeam(rootConfig.feedback) &&
-    !rootConfig.research.enabled &&
-    metadata !== undefined;
+  const cacheAllowed = reviewCacheAllowed({
+    bypassTriggerGate,
+    stack: Boolean(stackWalk),
+    feedback: feedbackNeedsRunSeam(rootConfig.feedback),
+    hasMetadata: metadata !== undefined,
+  });
   let cacheReadRoot: string | undefined;
   if (cacheAllowed) {
     try {

src/core/review-cache.ts

@@ -137,6 +137,32 @@ export async function reviewInputHash(options: ReviewInputHashOptions): Promise<
   return createHash("sha256").update(canonicalJson(input)).digest("hex");
 }
 
+/**
+ * Whether a run may reuse a cached result at all — the single definition of that
+ * policy, shared by the legacy and routed CI paths.
+ *
+ * It lives here because it was previously written out twice, once per path, and
+ * the copies drifted: when the offline index was removed, only the legacy copy
+ * dropped its research gate, so every routed repo silently kept running fresh
+ * reviews for a reason that no longer existed. Two expressions of one policy is
+ * the bug; one function that both paths call is the fix.
+ *
+ * Each flag means "this run has an input the cache key does not represent":
+ * dynamic stack context and model-backed reply adjudication both reach outside
+ * the scoped diff, and a maintainer's explicit /review is always a real rerun.
+ */
+export function reviewCacheAllowed(run: {
+  bypassTriggerGate: boolean;
+  /** Stack walking is on for this run. */
+  stack: boolean;
+  /** A feedback seam runs this pass (adjudication), not merely annotation. */
+  feedback: boolean;
+  /** PR metadata resolved; without it there is nothing stable to key on. */
+  hasMetadata: boolean;
+}): boolean {
+  return !run.bypassTriggerGate && !run.stack && !run.feedback && run.hasMetadata;
+}
+
 /** Partial/failed reviews must be retried, never made durable by a cache hit. */
 export function reviewCanBeReused(review: CoordinatorOutput): boolean {
   return review.couldNotComplete !== true && review.incomplete.length === 0;