diff --git a/core/src/shared/room-share.js b/core/src/shared/room-share.js
index 4f654f4cd..9b078f6ea 100644
--- a/core/src/shared/room-share.js
+++ b/core/src/shared/room-share.js
@@ -212,11 +212,23 @@ export function parseRoomShare(text) {
   if (at < 0) return undefined
   const start = raw.indexOf('{', at)
   if (start < 0) return undefined
+  // A chat line's text is a JSON string inside the object, so a brace in what someone typed is a
+  // character, not structure: the scan tracks strings and escapes, or one `{` would end the object
+  // early and drop the whole envelope (#855 reads the same tail this way).
   let depth = 0
   let end = -1
+  let inString = false
+  let escaped = false
   for (let i = start; i < raw.length; i += 1) {
     const ch = raw[i]
-    if (ch === '{') depth += 1
+    if (inString) {
+      if (escaped) escaped = false
+      else if (ch === '\\') escaped = true
+      else if (ch === '"') inString = false
+      continue
+    }
+    if (ch === '"') inString = true
+    else if (ch === '{') depth += 1
     else if (ch === '}') {
       depth -= 1
       if (depth === 0) { end = i; break }
diff --git a/core/test/room-share-braces.test.js b/core/test/room-share-braces.test.js
new file mode 100644
index 000000000..2afa87532
--- /dev/null
+++ b/core/test/room-share-braces.test.js
@@ -0,0 +1,39 @@
+// A room-share envelope is one JSON object after a marker line, and a chat line's text is a JSON
+// string inside it: `{` and `}` in that text are ordinary characters, not structure. The scan that
+// finds the object's end must therefore know when it is inside a string (and inside an escape), the
+// same way the social plugin's own tail reader does (#855) — otherwise one brace in what someone
+// typed drops the whole envelope.
+import { test } from 'node:test'
+import assert from 'node:assert/strict'
+import { encodeRoomShare, parseRoomShare } from '../src/shared/room-share.js'
+
+const line = (text) => parseRoomShare(encodeRoomShare({ op: 'line', roomId: 'r1', seq: 7, who: 'Alice', text }))
+
+test('a line whose text opens a brace is read back, not dropped', () => {
+  const parsed = line('if (x) { y()')
+  assert.equal(parsed?.op, 'line')
+  assert.equal(parsed?.roomId, 'r1')
+  assert.equal(parsed?.text, 'if (x) { y()')
+})
+
+test('a line whose text closes a brace is read back, not dropped', () => {
+  assert.equal(line('so the closing brace is }')?.text, 'so the closing brace is }')
+})
+
+test('a brace right after an escaped quote is still inside the string', () => {
+  assert.equal(line('say "{" now')?.text, 'say "{" now')
+})
+
+test('a copied history line keeps braces too', () => {
+  const wire = encodeRoomShare({ op: 'join', roomId: 'abc123', seq: 3, who: 'Alice', history: [{ who: 'Bob', text: 'map { a: 1 }' }] })
+  assert.equal(parseRoomShare(wire)?.history?.[0]?.text, 'map { a: 1 }')
+})
+
+test('plain text and balanced braces keep their current reading', () => {
+  assert.equal(line('plain text')?.text, 'plain text')
+  assert.equal(line('a {b} c')?.text, 'a {b} c')
+})
+
+test('a truncated envelope is still no envelope', () => {
+  assert.equal(parseRoomShare('FLYBOT-ROOM-SHARE\n{"v":1,"op":"line","roomId":"r1"'), undefined)
+})
diff --git a/patches/ds-bot/files/src/shared/room-share.js b/patches/ds-bot/files/src/shared/room-share.js
index 4f654f4cd..9b078f6ea 100644
--- a/patches/ds-bot/files/src/shared/room-share.js
+++ b/patches/ds-bot/files/src/shared/room-share.js
@@ -212,11 +212,23 @@ export function parseRoomShare(text) {
   if (at < 0) return undefined
   const start = raw.indexOf('{', at)
   if (start < 0) return undefined
+  // A chat line's text is a JSON string inside the object, so a brace in what someone typed is a
+  // character, not structure: the scan tracks strings and escapes, or one `{` would end the object
+  // early and drop the whole envelope (#855 reads the same tail this way).
   let depth = 0
   let end = -1
+  let inString = false
+  let escaped = false
   for (let i = start; i < raw.length; i += 1) {
     const ch = raw[i]
-    if (ch === '{') depth += 1
+    if (inString) {
+      if (escaped) escaped = false
+      else if (ch === '\\') escaped = true
+      else if (ch === '"') inString = false
+      continue
+    }
+    if (ch === '"') inString = true
+    else if (ch === '{') depth += 1
     else if (ch === '}') {
       depth -= 1
       if (depth === 0) { end = i; break }
diff --git a/patches/ds-bot/files/test/room-share-braces.test.js b/patches/ds-bot/files/test/room-share-braces.test.js
new file mode 100644
index 000000000..2afa87532
--- /dev/null
+++ b/patches/ds-bot/files/test/room-share-braces.test.js
@@ -0,0 +1,39 @@
+// A room-share envelope is one JSON object after a marker line, and a chat line's text is a JSON
+// string inside it: `{` and `}` in that text are ordinary characters, not structure. The scan that
+// finds the object's end must therefore know when it is inside a string (and inside an escape), the
+// same way the social plugin's own tail reader does (#855) — otherwise one brace in what someone
+// typed drops the whole envelope.
+import { test } from 'node:test'
+import assert from 'node:assert/strict'
+import { encodeRoomShare, parseRoomShare } from '../src/shared/room-share.js'
+
+const line = (text) => parseRoomShare(encodeRoomShare({ op: 'line', roomId: 'r1', seq: 7, who: 'Alice', text }))
+
+test('a line whose text opens a brace is read back, not dropped', () => {
+  const parsed = line('if (x) { y()')
+  assert.equal(parsed?.op, 'line')
+  assert.equal(parsed?.roomId, 'r1')
+  assert.equal(parsed?.text, 'if (x) { y()')
+})
+
+test('a line whose text closes a brace is read back, not dropped', () => {
+  assert.equal(line('so the closing brace is }')?.text, 'so the closing brace is }')
+})
+
+test('a brace right after an escaped quote is still inside the string', () => {
+  assert.equal(line('say "{" now')?.text, 'say "{" now')
+})
+
+test('a copied history line keeps braces too', () => {
+  const wire = encodeRoomShare({ op: 'join', roomId: 'abc123', seq: 3, who: 'Alice', history: [{ who: 'Bob', text: 'map { a: 1 }' }] })
+  assert.equal(parseRoomShare(wire)?.history?.[0]?.text, 'map { a: 1 }')
+})
+
+test('plain text and balanced braces keep their current reading', () => {
+  assert.equal(line('plain text')?.text, 'plain text')
+  assert.equal(line('a {b} c')?.text, 'a {b} c')
+})
+
+test('a truncated envelope is still no envelope', () => {
+  assert.equal(parseRoomShare('FLYBOT-ROOM-SHARE\n{"v":1,"op":"line","roomId":"r1"'), undefined)
+})