diff --git a/src/review/linked-issue-satisfaction-cache-input.ts b/src/review/linked-issue-satisfaction-cache-input.ts
index c09dd619ea..c08b0f771b 100644
--- a/src/review/linked-issue-satisfaction-cache-input.ts
+++ b/src/review/linked-issue-satisfaction-cache-input.ts
@@ -18,15 +18,19 @@ export type LinkedIssueSatisfactionCacheInput = {
 };
 
 export async function linkedIssueSatisfactionCacheInputFingerprint(input: LinkedIssueSatisfactionCacheInput): Promise<string> {
-  const payload = [
-    LINKED_ISSUE_SATISFACTION_CACHE_INPUT_VERSION,
-    input.byok ? "1" : "0",
-    input.provider ?? "",
-    input.model ?? "",
-    input.issueText ?? "",
-    input.prTitle ?? "",
-    input.prBody ?? "",
-    input.diff ?? "",
-  ].join("|");
-  return `${LINKED_ISSUE_SATISFACTION_CACHE_INPUT_VERSION}:${await sha256Hex(payload)}`;
+  // Structurally-delimited payload (mirrors ai-slop-cache-input.ts): a bare "|"-join of free-form
+  // GitHub text let an unescaped "|" inside one field shift a field boundary, so two genuinely different
+  // inputs could serialize identically and collide on the same fingerprint. JSON.stringify escapes the
+  // field values, so distinct inputs always produce distinct payloads.
+  const payload = {
+    version: LINKED_ISSUE_SATISFACTION_CACHE_INPUT_VERSION,
+    byok: input.byok,
+    provider: input.provider ?? "",
+    model: input.model ?? "",
+    issueText: input.issueText ?? "",
+    prTitle: input.prTitle ?? "",
+    prBody: input.prBody ?? "",
+    diff: input.diff ?? "",
+  };
+  return `${LINKED_ISSUE_SATISFACTION_CACHE_INPUT_VERSION}:${await sha256Hex(JSON.stringify(payload))}`;
 }
diff --git a/test/unit/linked-issue-satisfaction-cache.test.ts b/test/unit/linked-issue-satisfaction-cache.test.ts
index 1d94133c61..bf1b7a894b 100644
--- a/test/unit/linked-issue-satisfaction-cache.test.ts
+++ b/test/unit/linked-issue-satisfaction-cache.test.ts
@@ -47,6 +47,16 @@ describe("linked-issue satisfaction cache (#1961/#3906)", () => {
     expect(await getCachedLinkedIssueSatisfaction(env, "o/r", 9, "sha1", 1, freeFingerprint)).toEqual({ status: "ok", result: { status: "partial", rationale: "r", confidence: 0.7 }, estimatedNeurons: 6 });
   });
 
+  it("does not collide when a '|' inside one text field would shift a delimiter boundary (#5939)", async () => {
+    // A bare "|"-join let an unescaped "|" move a field boundary: {issueText: "foo|bar", prTitle: "baz"}
+    // and {issueText: "foo", prTitle: "bar|baz"} (other fields equal) serialized identically and hashed
+    // to the same fingerprint. JSON.stringify escapes the field values, so the two stay distinct.
+    const base = { byok: false, provider: null, model: null } as const;
+    const a = await linkedIssueSatisfactionCacheInputFingerprint({ ...base, issueText: "foo|bar", prTitle: "baz" });
+    const b = await linkedIssueSatisfactionCacheInputFingerprint({ ...base, issueText: "foo", prTitle: "bar|baz" });
+    expect(a).not.toBe(b);
+  });
+
   it("upserts — a re-run at the same key replaces the stored assessment", async () => {
     const env = createTestEnv();
     const fingerprint = await fp();