core: request accumulates 52 images, exceeds provider max of 50

Summary

Upstream request fails with [invalid_request_error] request contains 52 images, exceeding the maximum of 50 allowed per request after iterating on image assets in a single session.

Environment

• opencode version: 1.18.21 (opencode2 v0.0.0-beta-19157)
• OS: Darwin 25.6.0 arm64
• Terminal: TERM=xterm-256color, TERM_PROGRAM=ghostty, COLORTERM=truecolor
• Shell: /bin/zsh
• Install/channel: beta
• Active plugins: none found (no .opencode/plugin or .opencode/plugins; config has minimax provider + exa remote MCP only)

Reproduction

1. In one session, iteratively build HTML visuals rendered via headless Chrome.
2. Have the agent read PNG/GIF outputs after each iteration (hero-banner.png, anatomy-eta.png, decision-2am.png, plus GIF previews).
3. After ~10-15 image reads across turns, any new request fails.
4. Error: Error from provider (Console): Upstream request failed: [invalid_request_error] request contains 52 images, exceeding the maximum of 50 allowed per request

Expected Behavior

Old image attachments should be compacted, dropped, or blocked before hitting the provider cap — or at least warn with a way to continue text-only.

Actual Behavior

Request hard-fails at 52/50 images. Session is stuck: can't send even text-only prompts without hitting the image count.

Additional Context

• Earlier in same session also saw: Unable to process image(s). Mouse mode is currently enabled, which limits image messages to one image per message.
• Workflow: Substack visual iteration (1600px HTML -> Chrome screenshot -> read PNG). No manual image uploads, only agent read tool outputs.
• Frequency: consistent once cap is hit; blocks the session.
• Workaround tried: none yet — reporter asked agent to stop sending images. Proposed: new session / text-only mode.