[BUG] VS Code extension: pasting a very large screenshot causes runaway memory (~190GB footprint) and repeated macOS kernel panics

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

[BUG] VS Code extension: pasting a very large screenshot causes runaway memory (~190GB footprint) and repeated macOS kernel panics

Summary

Pasting a large full-screen Retina screenshot (5712×4284 px, ~90MB PNG → ~120MB as base64) into the Claude Code VS Code extension chat caused unbounded memory growth that exhausted 64GB of RAM plus swap and kernel-panicked the machine (watchdog timeout) three times in one day. The extension performs no client-side size validation on pasted images (the Anthropic API limit is 5MB per image), and once the oversized message enters the webview → extension host → CLI pipeline, memory grows at roughly GB/minute until the system dies.

Because VS Code restores the session after reboot and the user naturally retries the conversation, the crash re-triggers shortly after every restart — a crash loop at the whole-machine level.

Environment

• Claude Code VS Code extension: 2.1.201 (anthropic.claude-code-2.1.201-darwin-arm64)
• Claude Code CLI (bundled native binary): 2.1.201
• VS Code: 1.127.0
• macOS: 26.5.1 (25F80), Apple Silicon (Mac15,9, 16 cores, 64GB RAM)

What happened (timeline, 2026-07-06, times BST)

| Time | Event |
|---|---|
| ~10:39–16:12 | Long Claude Code session in the extension (3 image attachments over the day) |
| ~16:13 | Kernel panic #1 (watchdog timeout — memory exhaustion) |
| 16:14 | Reboot; VS Code restores; new Claude session resumed |
| ~16:27 | Kernel panic #2 — only ~13 minutes after boot |
| 16:28 | Reboot; VS Code restores |
| 16:44:59 | User pastes full-screen screenshot into the chat; the extension logs a single 120,078,654-byte log line containing the entire base64 image. This is the last entry the extension ever logs |
| 17:06 | macOS flags the extension-spawned node process for sustained disk writes: 2,147.49MB dirtied over 2,164s (~1MB/s) (node_2026-07-06-170603 resource diag) |
| 17:08 | JetsamEvent: system memory exhausted. Compressor holds 1,494,235 compressed pages storing 11,603,169 uncompressed pages ≈ 190GB — an ~8:1 ratio consistent with highly repetitive data (duplicated base64 text). VS Code relaunches |
| ~17:28 | User retries the session; kernel panic #3 |

Activity Monitor attributed ~200GB of memory footprint to the VS Code process group before each crash.

Evidence (attached zip)

• JetsamEvent-2026-07-06-170817.ips — kernel memory-exhaustion event; see memoryStatus.uncompressed = 11,603,169 pages × 16KB ≈ 190GB
• panic-base+socd-2026-07-06-{161509,162954,173112}.000.panic — three kernel panics, all watchdog timeout: no checkins from watchdogd
• node_2026-07-06-170603_Bens-MacBook-Pro.diag — disk-writes resource violation by a node process in the com.microsoft.VSCode coalition, spanning boot → jetsam
• claude-vscode-extension-log-REDACTED.txt — structure of the 120MB single-line extension log entry (Received message from webview with inline base64 image), base64 payload redacted

Session transcript last-write times in ~/.claude/projects/ correlate 1:1 with all three panics (16:12, 16:23→~16:27 panic, 17:07→17:08 jetsam, 17:28→panic).

Steps to reproduce

1. On macOS, take a full-screen screenshot on a Retina display showing photo-heavy content (mine was 5712×4284; the PNG was ~90MB because photographic content defeats PNG compression)
2. Paste it into the Claude Code VS Code extension chat with a short prompt and send
3. Watch the VS Code process group's memory footprint in Activity Monitor

Observed: memory grows on the order of GB/minute; extension logging stops entirely after the paste; within ~20–60 minutes (64GB RAM + fast SSD swap) the system watchdog-panics.

Expected behavior

• The extension should validate pasted-image size client-side and downscale or reject images exceeding API limits (5MB per image) instead of ingesting a 120MB base64 payload
• Whatever pipeline stage duplicates the message (webview ↔ extension host ↔ CLI stream-json replay) should not retain unbounded copies — ~190GB / ~120MB suggests on the order of 1,500+ retained copies of the same string
• The extension should not write a 120MB single-line entry to the output-channel log

Related issues

Possibly the same underlying leak as #21182, #22716, #12814 — this report adds a deterministic amplifier (oversized pasted image) and full kernel-level forensics.

claude-code-bug-evidence.zip

What Should Happen?

The extension should validate pasted-image size client-side and downscale or reject images exceeding the API limit (5MB per image), rather than ingesting a 120MB base64 payload. Oversized or not, a single pasted image should never cause unbounded memory growth (~190GB footprint, ~1,500+ retained copies of the same string) that exhausts RAM and swap and kernel-panics the machine. The extension also should not write the full 120MB payload as a single output-channel log line.

Error Messages/Logs

Kernel panic (x3 on 2026-07-06, at 16:15, 16:29, 17:31 BST): panic(cpu 10 caller 0xfffffe0051b4ca4c): watchdog timeout: no checkins from watchdogd in 94 seconds (355 total checkins since monitoring last enabled)

JetsamEvent-2026-07-06-170817.ips (memoryStatus): compressorSize: 1494235 pages, uncompressed: 11603169 pages (~190GB @ 16KB/page) largestZone: compressor_segment

node_2026-07-06-170603 resource diag (extension-spawned node, coalition com.microsoft.VSCode): Writes: 2147.49 MB of file backed memory dirtied over 2164 seconds (992.47 KB per second average), exceeding limit of 24.86 KB per second

Extension log (Claude VSCode.1.log): final entry at 16:44:59 is a single 120,078,654-byte line — "Received message from webview" containing one pasted image as base64 (120,078,196 chars ≈ 90MB PNG, 5712x4284 px). No further log output until the system died. Full files in attached zip.

Steps to Reproduce

1. macOS, 64GB RAM, VS Code 1.127.0 with Claude Code extension 2.1.201, Opus 4.8
2. Take a full-screen screenshot on a Retina display showing photo-heavy content

(mine was 5712x4284; the PNG was ~90MB because photographic content defeats
PNG compression)

1. Paste it into the Claude Code extension chat panel with a short prompt and send
2. Watch the VS Code process group in Activity Monitor: memory grows ~GB/minute,

extension logging stops, and within ~20-60 minutes the machine watchdog-panics
(repeated 3x in one day — VS Code restores the session after reboot, and
retrying the conversation re-triggers the crash)

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.201 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_