feat(truncate): allow configuring tool output truncation limits

[1rgs]

Issue for this PR

Closes #22565

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Moves the tool-output truncation thresholds (MAX_LINES = 2000, MAX_BYTES = 50 * 1024 in packages/opencode/src/tool/truncate.ts) from hardcoded constants into optional opencode config.

New config:

{ "tool_output": { "max_lines": 5000, "max_bytes": 204800 } }

Truncate.Service gains a limits() method that reads those values from Config.Service and falls back to the existing constants. output() uses it as the default, so callers that pass {} (e.g. Tool.wrap) pick up the config without any change at the call site.

Config.Service is read with Effect.serviceOption, so tests and any other caller of Truncate.defaultLayer that doesn't provide Config keep working and get the original defaults.

bash.ts also read Truncate.MAX_LINES / Truncate.MAX_BYTES directly in two spots (its internal streaming cap, and the ${maxLines} / ${maxBytes} placeholders it substitutes into the tool description shown to the model) — switched both to trunc.limits() so the advertised and enforced limits track config.

How did you verify your code works?

Tests from packages/opencode:

$ bun test test/tool/truncation.test.ts test/tool/bash.test.ts
 40 pass
 0 fail

The new truncation tests mock Config.Service via Layer.mock and assert:

• limits() returns { maxLines: 123, maxBytes: 456 } when config sets those
• output() with a 100-line input truncates to "...90 lines truncated..." when max_lines: 10, max_bytes: 1 MB (isolates the line path)
• output() with a 1000-byte input shows "bytes truncated..." when max_lines: 1_000_000, max_bytes: 100 (isolates the byte path)
• Per-call options.maxLines / options.maxBytes still override config
• Without Config in context, limits() returns the existing MAX_LINES / MAX_BYTES — the test file's default layer is unchanged, so the other 15 tests also prove the no-config path

Also passing:

• bun run typecheck in packages/opencode (tsgo --noEmit)
• Pre-push turbo typecheck over all 13 workspace packages

Reproducing manually: drop {"tool_output":{"max_lines":10,"max_bytes":1048576}} into your opencode config and run a bash command whose output exceeds 10 lines — it truncates at 10 instead of 2000.

Screenshots / recordings

N/A — no UI changes.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

Thanks for updating your PR! It now meets our contributing guidelines. 👍