Desktop (macOS): renderer V8 OOM crash loop when pasting large JSON into composer (parsePromptInputV2Editor)

Environment

• OpenCode Desktop 1.18.21 (auto-updated from 1.18.20 right before first crash), macOS arm64, Electron 42.3.3 / Chrome 148 / Node 24.15.0

Summary

Pasting a large nested JSON blob (~165 KB session-export) into the chat composer crashes the renderer with a V8 heap OOM abort (render-process-gone, reason: crashed, exitCode: 5). If the pasted payload persists in the composer's prompt-history store, every subsequent app launch re-feeds it through the same parser and the renderer OOMs again within ~17 s — an unbootable crash loop.

Evidence

Both Crashpad minidumps carry identical V8 OOM crash keys and JS stacks:

v8-oom-location: Ineffective mark-compacts near heap limit
#0 (anonymous)             oc://renderer/assets/main-DxX1DkV8.js:128219:89
#1 parsePromptInputV2Editor                              :128219:60
#2 PromptInputV2._el$6.$$input                           :127950:22
#3 handleNode                                            :1800:64
#4 eventHandler                                          :1821:12
#5 onPaste                                               :129485:66

GC log at death:
  3847.2 (3917.9) -> 3847.1 (3917.7) MB ... last resort; GC in old space requested
  MarkCompactCollector: young object promotion failed

Heap pinned at ~3.85 GB against V8's ~4 GB ceiling in both crashes:

• Crash 1: paste at T+9 min → ~10 min of ResizeObserver/layout thrash → OOM.
• Crash 2 (relaunch): renderer hit 3.85 GB within 17 s of process start, no user input — consistent with persisted prompt-history being re-parsed on boot.

Ruled out: server-side session data (largest session ≈ 2.4 MB total parts), localStorage/IndexedDB (<150 KB), GPU.

Workaround that unblocked the machine

Delete the oversized entry from the desktop KV store while the app is closed:

sqlite3 "$HOME/Library/Application Support/ai.opencode.desktop/drafts.sqlite" \
  "UPDATE document SET value='{\"entries\":[]}' WHERE key LIKE '%prompt-history%';"

(Back up the file first.) Renderer then boots and stays healthy.

Suggested fixes

1. Size-clamp paste input in parsePromptInputV2Editor (reject or truncate above e.g. 1–2 MB with a toast instead of parsing).
2. Cap per-entry size/count in persisted prompt-history; don't restore entries above the clamp on boot.
3. Treat paste-path allocation failures as recoverable (fail soft) rather than letting V8 abort the process.

Happy to share the two .dmp files if useful (Crashpad shows them as pending upload).