diff --git a/packages/shared/src/index.ts b/packages/shared/src/index.ts
index cbb2b9e49bf..30f5ca5ef22 100644
--- a/packages/shared/src/index.ts
+++ b/packages/shared/src/index.ts
@@ -2353,6 +2353,7 @@ export {
   type EnvironmentCustomImageTerminalSessionToken,
 } from "./validators/environment-custom-images.js";
 export * from "./validators/skill-policy.js";
+export { normalizeMarkdownBody } from "./validators/text.js";
 export {
   FEATURE_TIERS,
   INSTANCE_FEATURE_CATALOG,
diff --git a/packages/shared/src/validators/index.ts b/packages/shared/src/validators/index.ts
index d93c6649dd6..df169578136 100644
--- a/packages/shared/src/validators/index.ts
+++ b/packages/shared/src/validators/index.ts
@@ -914,4 +914,5 @@ export {
   type RevokeToolTrustRule,
 } from "./tool-access.js";
 export * from "./skill-policy.js";
+export { normalizeMarkdownBody } from "./text.js";
 export * from "./app-definition.js";
diff --git a/packages/shared/src/validators/text.test.ts b/packages/shared/src/validators/text.test.ts
index ee30f51d8db..90950765bd8 100644
--- a/packages/shared/src/validators/text.test.ts
+++ b/packages/shared/src/validators/text.test.ts
@@ -57,6 +57,11 @@ describe("normalizeMidLineHeadings", () => {
     expect(normalizeMidLineHeadings(body)).toBe(body);
   });
 
+  it("does not close a long fence with a shorter run", () => {
+    const body = "````markdown\n```\ncode ## comment\n````";
+    expect(normalizeMidLineHeadings(body)).toBe(body);
+  });
+
   it("is a no-op when there is no `#` at all", () => {
     const body = "Just some prose with no markers.";
     expect(normalizeMidLineHeadings(body)).toBe(body);
@@ -71,8 +76,8 @@ describe("normalizeMarkdownBody / multilineTextSchema", () => {
     );
   });
 
-  it("multilineTextSchema self-heals a collapsed plan body on write", () => {
+  it("multilineTextSchema leaves unrelated mid-line markers unchanged", () => {
     const parsed = multilineTextSchema.parse("plan pack)## The goal, restated");
-    expect(parsed).toBe("plan pack)\n\n## The goal, restated");
+    expect(parsed).toBe("plan pack)## The goal, restated");
   });
 });
diff --git a/packages/shared/src/validators/text.ts b/packages/shared/src/validators/text.ts
index e00eade1155..1ecf46704bf 100644
--- a/packages/shared/src/validators/text.ts
+++ b/packages/shared/src/validators/text.ts
@@ -43,6 +43,7 @@ export function normalizeMidLineHeadings(value: string): string {
   const lines = value.split("\n");
   let inFence = false;
   let fenceChar = "";
+  let fenceLength = 0;
   const out: string[] = [];
   for (const line of lines) {
     const fenceMatch = FENCE_LINE.exec(line);
@@ -51,9 +52,11 @@ export function normalizeMidLineHeadings(value: string): string {
       if (!inFence) {
         inFence = true;
         fenceChar = marker[0]!;
-      } else if (marker[0] === fenceChar) {
+        fenceLength = marker.length;
+      } else if (marker[0] === fenceChar && marker.length >= fenceLength) {
         inFence = false;
         fenceChar = "";
+        fenceLength = 0;
       }
       out.push(line);
       continue;
@@ -67,4 +70,4 @@ export function normalizeMarkdownBody(value: string): string {
   return normalizeMidLineHeadings(normalizeEscapedLineBreaks(value));
 }
 
-export const multilineTextSchema = z.string().transform(normalizeMarkdownBody);
+export const multilineTextSchema = z.string().transform(normalizeEscapedLineBreaks);
diff --git a/server/src/__tests__/document-annotation-routes.test.ts b/server/src/__tests__/document-annotation-routes.test.ts
index 9584c2ebb1c..bddf1deb3c6 100644
--- a/server/src/__tests__/document-annotation-routes.test.ts
+++ b/server/src/__tests__/document-annotation-routes.test.ts
@@ -281,6 +281,32 @@ describe("document annotation routes", () => {
     expect(mockHeartbeatService.wakeup).not.toHaveBeenCalled();
   });
 
+  it("heals collapsed headings only for the plan document", async () => {
+    mockIssueService.getById.mockResolvedValue({
+      id: issueId,
+      companyId,
+      title: "Document API",
+      status: "in_progress",
+      assigneeAgentId: null,
+    });
+
+    await request(await createApp())
+      .put(`/api/issues/${issueId}/documents/plan`)
+      .send({ format: "markdown", body: "Intro)## Goal" })
+      .expect(200);
+    expect(mockDocumentService.upsertIssueDocument).toHaveBeenLastCalledWith(
+      expect.objectContaining({ body: "Intro)\n\n## Goal" }),
+    );
+
+    await request(await createApp())
+      .put(`/api/issues/${issueId}/documents/notes`)
+      .send({ format: "markdown", body: "Intro)## Legitimate inline text" })
+      .expect(200);
+    expect(mockDocumentService.upsertIssueDocument).toHaveBeenLastCalledWith(
+      expect.objectContaining({ body: "Intro)## Legitimate inline text" }),
+    );
+  });
+
   it("queues one bounded recovery when a board document revision expires the final review interactions", async () => {
     const assigneeAgentId = "99999999-9999-4999-8999-999999999999";
     mockIssueService.getById.mockResolvedValue({
diff --git a/server/src/routes/issues.ts b/server/src/routes/issues.ts
index beb6459dd62..e436d148537 100644
--- a/server/src/routes/issues.ts
+++ b/server/src/routes/issues.ts
@@ -68,6 +68,7 @@ import {
   getClosedIsolatedExecutionWorkspaceMessage,
   isClosedIsolatedExecutionWorkspace,
   isUuidLike,
+  normalizeMarkdownBody,
   normalizeIssueIdentifier as normalizeIssueReferenceIdentifier,
   type CompactIssue,
   type CompanySearchExtractQuery,
@@ -6676,7 +6677,7 @@ export function issueRoutes(
       key: keyParsed.data,
       title: req.body.title ?? null,
       format: req.body.format,
-      body: req.body.body,
+      body: keyParsed.data === "plan" ? normalizeMarkdownBody(req.body.body) : req.body.body,
       changeSummary: req.body.changeSummary ?? null,
       baseRevisionId: req.body.baseRevisionId ?? null,
       createdByAgentId: actor.agentId ?? null,