Bug: `read_file` line numbers are duplicated when using a sandbox backend

[rivalyotam]

Summary

When a file is read through any sandbox backend (BaseSandbox / its subclasses in libs/deepagents/src/backends/sandbox.ts), the output shows line numbers twice on every line, e.g.:

     1	     1	import { foo } from "bar";
     2	     2	const x = 1;

instead of the expected single column:

     1	import { foo } from "bar";
     2	const x = 1;

Root cause

Line numbering is applied in two places for sandbox reads:

1. The backend. buildReadCommand() in libs/deepagents/src/backends/sandbox.ts builds an awk command that prepends line numbers itself:

   awk 'NR >= ${start} && NR <= ${end} { printf "%6d\t%s\n", NR, $0 }' ${quotedPath}

2. The middleware. The shared read_file tool in libs/deepagents/src/middleware/fs.ts (line ~773) unconditionally re-numbers whatever content the backend returns:

   let formatted = formatContentWithLineNumbers(content, offset + 1);

Proposed fix

Change the awk command in buildReadCommand() to emit only the line content:

awk 'NR >= ${start} && NR <= ${end} { printf "%s\n", $0 }' ${quotedPath}

[Jonesxq]

Hi! I confirmed that the current main still has both numbering passes: BaseSandbox.buildReadCommand() prefixes lines in awk, and the shared read_file middleware formats them again.

I also found #439, which addresses the same issue but is based on an older main and has not received review or checks. Before duplicating work, would you prefer that PR to be revived, or may I take #679 with a focused patch against current main?

My proposed scope is to return raw paginated text from BaseSandbox.read(), add a regression test, update the related JSDoc, and include a patch changeset. I'm happy to proceed once the approach is approved and the issue is assigned.