room-share: one brace in a chat line's text drops the whole envelope #2447

Written-by: Delivery-1

Implementation: FlyBot (ours) — PR follows within the hour.

What happens

parseRoomShare finds the end of a room-share envelope by counting { and } from the first brace after the marker. It never tracks JSON string literals, so a { or } inside a chat line's text is counted as structure: the object looks finished too early, JSON.parse fails, and the whole envelope is dropped.

core/src/shared/room-share.js:209 at 5e71a07e (base delivery/ai-centric-development-service):

let depth = 0
let end = -1
for (let i = start; i < raw.length; i += 1) {
  const ch = raw[i]
  if (ch === '{') depth += 1
  else if (ch === '}') {
    depth -= 1
    if (depth === 0) { end = i; break }
  }
}

Braces are ordinary characters in a message, and people type them constantly (code, if (x) { … }, a lone } at the end of a dict). A balanced pair happens to survive because the two cancel out; one unbalanced brace loses the entire line.

Reproduction (at 5e71a07e, no source change)

import { encodeRoomShare, parseRoomShare } from './src/shared/room-share.js'
parseRoomShare(encodeRoomShare({ op: 'line', roomId: 'r1', seq: 7, who: 'Alice', text: 'if (x) { y()' }))
// actual:   undefined
// expected: an envelope with text 'if (x) { y()'

parseRoomShare(encodeRoomShare({ op: 'line', roomId: 'r1', seq: 7, who: 'Alice', text: 'so the closing brace is }' }))
// actual:   undefined

encodeRoomShare writes text with JSON.stringify, which leaves braces inside the string raw, so the envelope it produces is the one that cannot be read back.

What a person sees

• A sent line never arrives. The host routes a delivered share line through parseRoomShare (core/src/host/room-membership.js:2257 ingestRemoteRoomLine, :2371 applyInboundRoomShare). An unparsed envelope is not a room line at all, so the message is dropped instead of shown.
• A join loses its history. fitJoin/historyLine copy a room's recent lines into the join envelope; one brace in a copied line makes that whole join unparsable, so the guest's mirror stays empty and the room row reads as if no share arrived.
• The same shape was fixed once already on the client side (plugins/social/client.js envelopeTail, fix(social): read an envelope body carrying "}", and correct the stale blanket-hold comment #855) for held-line display; the shared parser that the host actually trusts was left with the naive scan, so the same text now breaks delivery instead of only a card's wording.

Expected behaviour

1. A line envelope whose text carries a single { or a single } parses, with op, roomId and the exact text preserved.
2. A brace right after an escaped quote (say "{" now) is still inside the string: the scan tracks \ escapes, so a \" does not end the literal.
3. A copied history line keeps its braces through a join envelope.
4. Controls, unchanged: plain text and balanced braces parse as today, and an envelope that really is truncated (no closing brace) still answers undefined.

Scope

• core/src/shared/room-share.js — parseRoomShare's object-end scan tracks string literals and escapes (the algorithm plugins/social/client.js envelopeTail already uses after fix(social): read an envelope body carrying "}", and correct the stale blanket-hold comment #855). Nothing else in the module moves: no field bound, no op rule, no marker rule, and isRoomShareText is untouched.
• core/test/room-share-braces.test.js — the six cases above (three red on the base tree).
• Generated, not hand-edited: patches/ds-bot/files/src/shared/room-share.js, patches/ds-bot/files/test/room-share-braces.test.js. core/client.js is unchanged — src/client/ does not import this module.

Red first (base 5e71a07e, before the source change)

$ cd core && TZ=UTC node --import ./test/harness-resolve.mjs --test test/room-share-braces.test.js
not ok 1 - a line whose text opens a brace is read back, not dropped
not ok 2 - a line whose text closes a brace is read back, not dropped
not ok 3 - a brace right after an escaped quote is still inside the string
# tests 6 / # pass 3 / # fail 3

Cases 4–6 (history braces, plain/balanced controls, truncated envelope) pass before and after, so the fix cannot loosen the envelope's rejection of a genuinely broken body.

Duplicate check

Searched room share envelope brace, parseRoomShare, room-share brace: #855 (closed) is the client-side envelopeTail fix in plugins/social/client.js — same class, different file, and it explicitly left core/src/shared/room-share.js alone; #1928/#1933/#1937 are code-point/well-formedness bounds in the same module, none about the object-end scan. No open or closed issue covers this shared parser, and no open or closed PR carries this file change.