grep tool silently returns empty results when the search path does not exist

Summary

The grep tool silently returns an empty result set when the configured path (directory or file) does not exist, instead of reporting an error. This masks typos and misconfigured working directories: a user searching path: "src/utlis" (sic) gets zero matches with no indication that the path is wrong, and may conclude the codebase has no hits.

Expected

When the search path cannot be resolved, grep should fail with a clear ToolFailure (e.g. "path does not exist: ") so the agent can correct the argument, matching the behavior of read/glob when their targets are missing.

Actual

Grep tool returns { content: { files: [], numFiles: 0, content: "" } } for a non-existent path. The underlying FSUtil.find/realpath call degrades to an empty result, and the error is swallowed.

Environment

• opencode version: dev
• grep invoked with pattern + path pointing at a missing directory/file

Start at the grep tool's handling of FSUtil.find and the realpath call for the configured path. Compare how read and glob report missing targets, then make a missing file or directory produce a clear ToolFailure instead of an empty result set and verify the returned error and result behavior.