#138 fix(opencode): share tool response truncation

Summary

• use the existing tool-response truncator for successful output, persisted tool errors, workflow-tool errors, and malformed tool-call repairs
• reduce the shared default limit from 50 KiB to 40 KiB while retaining the existing 2,000-line limit and configuration overrides
• save complete truncated content in the existing seven-day tool-output store and return the same head preview plus file path
• keep a bounded preview if the archive write fails, for both successful responses and errors

Why

A production malformed browser_execute call contained roughly 118,000 newline characters. AI SDK InvalidToolInputError copied the malformed tool input into its error, and JSON reserialization persisted a roughly 445,000-character assistant message. A later tiny user turn then exceeded model context. Normal tool-output truncation did not apply because the oversized content crossed the boundary as tool input and error rather than successful output.

Validation

• bun test test/tool/truncation.test.ts test/session/session.test.ts: 28 passed
• production-shaped 118,000-newline malformed-input regression: passed and full error archived
• shell truncation regressions: 4 passed
• packages/opencode bun typecheck: passed
• root filtered typecheck: 16 packages passed
• targeted oxlint: 0 errors
• Prettier and git diff --check: passed
• repository pre-push hook with Bun 1.3.14: passed

Scope

The final diff is four files. Three source integration points remain necessary: the shared truncator, the central persisted-tool-error boundary, and the AI SDK malformed-call repair boundary.