diff --git a/server/src/__tests__/issue-comment-run-retry-dedup.test.ts b/server/src/__tests__/issue-comment-run-retry-dedup.test.ts
new file mode 100644
index 00000000000..17195377ab9
--- /dev/null
+++ b/server/src/__tests__/issue-comment-run-retry-dedup.test.ts
@@ -0,0 +1,61 @@
+import { randomUUID } from "node:crypto";
+import { afterAll, afterEach, beforeAll, describe, expect, it } from "vitest";
+import { agents, companies, createDb, heartbeatRuns, instanceSettings, issueComments, issues } from "@paperclipai/db";
+import { getEmbeddedPostgresTestSupport, startEmbeddedPostgresTestDatabase } from "./helpers/embedded-postgres.js";
+import { issueService } from "../services/issues.js";
+
+const embeddedPostgresSupport = await getEmbeddedPostgresTestSupport();
+const describeEmbeddedPostgres = embeddedPostgresSupport.supported ? describe : describe.skip;
+
+describeEmbeddedPostgres("issueService.addCommentWithRunRetryDedup", () => {
+  let db!: ReturnType<typeof createDb>;
+  let tempDb: Awaited<ReturnType<typeof startEmbeddedPostgresTestDatabase>> | null = null;
+
+  beforeAll(async () => {
+    tempDb = await startEmbeddedPostgresTestDatabase("paperclip-comment-run-retry-");
+    db = createDb(tempDb.connectionString);
+  }, 20_000);
+
+  afterEach(async () => {
+    await db.delete(issueComments);
+    await db.delete(issues);
+    await db.delete(heartbeatRuns);
+    await db.delete(agents);
+    await db.delete(instanceSettings);
+    await db.delete(companies);
+  });
+
+  afterAll(async () => {
+    await tempDb?.cleanup();
+  });
+
+  it("collapses repeated writes from the same run, author, and body", async () => {
+    const companyId = randomUUID();
+    const agentId = randomUUID();
+    const issueId = randomUUID();
+    const runId = randomUUID();
+    await db.insert(companies).values({ id: companyId, name: "Paperclip", issuePrefix: "TDEDUP" });
+    await db.insert(agents).values({
+      id: agentId,
+      companyId,
+      name: "Coder",
+      role: "engineer",
+      status: "active",
+      adapterType: "codex_local",
+      adapterConfig: {},
+      runtimeConfig: {},
+      permissions: {},
+    });
+    await db.insert(heartbeatRuns).values({ id: runId, companyId, agentId, status: "running" });
+    await db.insert(issues).values({ id: issueId, companyId, title: "Retry target", status: "in_progress", priority: "medium" });
+
+    const svc = issueService(db);
+    const first = await svc.addCommentWithRunRetryDedup(issueId, "Same update", { agentId, runId });
+    const second = await svc.addCommentWithRunRetryDedup(issueId, "Same update", { agentId, runId });
+
+    expect(first.reused).toBe(false);
+    expect(second.reused).toBe(true);
+    expect(second.comment.id).toBe(first.comment.id);
+    await expect(db.select().from(issueComments)).resolves.toHaveLength(1);
+  });
+});
diff --git a/server/src/routes/issues.ts b/server/src/routes/issues.ts
index 9d1fc60eabc..b2ce3cef4ab 100644
--- a/server/src/routes/issues.ts
+++ b/server/src/routes/issues.ts
@@ -9735,6 +9735,7 @@ export function issueRoutes(
     // Without a single transaction, a 422 (or any error) thrown by the status update after the
     // comment is inserted would leave an orphan comment without the corresponding state change.
     let comment: Awaited<ReturnType<typeof svc.addComment>>;
+    let reusedComment = false;
     if (shouldAutoApproveReviewComment) {
       const transition = applyIssueExecutionPolicyTransition({
         issue: currentIssue,
@@ -9848,16 +9849,27 @@ export function issueRoutes(
         requestedByActorId: actor.actorId,
       });
     } else {
-      comment = await svc.addComment(id, req.body.body, {
+      const commentActor = {
         agentId: actor.agentId ?? undefined,
         userId: actor.actorType === "user" ? actor.actorId : undefined,
         runId: actor.runId,
-      }, {
+      };
+      const commentOptions = {
         authorType: req.body.authorType ?? (actor.actorType === "agent" ? "agent" : "user"),
         presentation: req.body.presentation ?? null,
         metadata: req.body.metadata ?? null,
         sourceTrust: await sourceTrustForActorWrite(currentIssue, actor),
-      });
+      };
+      const result = typeof svc.addCommentWithRunRetryDedup === "function"
+        ? await svc.addCommentWithRunRetryDedup(id, req.body.body, commentActor, commentOptions)
+        : { comment: await svc.addComment(id, req.body.body, commentActor, commentOptions), reused: false };
+      comment = result.comment;
+      reusedComment = result.reused;
+    }
+
+    if (reusedComment) {
+      res.status(200).json(comment);
+      return;
     }
 
     await issueReferencesSvc.syncComment(comment.id);
diff --git a/server/src/services/issues.ts b/server/src/services/issues.ts
index ce1e36d53cf..413a93b636f 100644
--- a/server/src/services/issues.ts
+++ b/server/src/services/issues.ts
@@ -7362,6 +7362,50 @@ export function issueService(db: Db) {
       return redactIssueComment(comment, currentUserRedactionOptions.enabled);
     },
 
+    addCommentWithRunRetryDedup: async (
+      issueId: string,
+      body: string,
+      actor: { agentId?: string; userId?: string; runId?: string | null },
+      options?: {
+        authorType?: IssueCommentAuthorType | null;
+        presentation?: IssueCommentPresentation | null;
+        metadata?: IssueCommentMetadata | null;
+        sourceTrust?: typeof issueComments.$inferInsert.sourceTrust;
+        createdAt?: Date | string | null;
+      },
+    ) => {
+      if (!actor.runId) {
+        return { comment: await issueService(db).addComment(issueId, body, actor, options), reused: false };
+      }
+      const runId = actor.runId;
+      return db.transaction(async (tx) => {
+        const guardKey = `issue-comment:run-retry:${issueId}:${runId}:${actor.agentId ?? actor.userId ?? "system"}:${body}`;
+        await tx.execute(sql`select pg_advisory_xact_lock(hashtextextended(${guardKey}, 0))`);
+        const currentUserRedactionOptions = {
+          enabled: (await instanceSettings.getGeneral()).censorUsernameInLogs,
+        };
+        const redactedBody = redactCurrentUserText(body, currentUserRedactionOptions);
+        const existing = await tx
+          .select()
+          .from(issueComments)
+          .where(and(
+            eq(issueComments.issueId, issueId),
+            eq(issueComments.createdByRunId, runId),
+            actor.agentId ? eq(issueComments.authorAgentId, actor.agentId) : isNull(issueComments.authorAgentId),
+            actor.userId ? eq(issueComments.authorUserId, actor.userId) : isNull(issueComments.authorUserId),
+            eq(issueComments.body, redactedBody),
+            isNull(issueComments.deletedAt),
+          ))
+          .orderBy(asc(issueComments.createdAt))
+          .then((rows) => rows[0] ?? null);
+        if (existing) {
+          return { comment: redactIssueComment(existing, currentUserRedactionOptions.enabled), reused: true };
+        }
+        const comment = await issueService(db).addComment(issueId, body, actor, options, tx);
+        return { comment, reused: false };
+      });
+    },
+
     createAttachment: async (input: {
       issueId: string;
       issueCommentId?: string | null;