fix: honor built-in tool contracts

[yanpgwang]

Problem

The model-facing read schema advertises line ranges, but the executor ignored them. Large tool results explicitly tell the Agent to use that range, so the recovery path was not actually closed. The bash schema also advertised restart even though Mango runs independent sandbox commands and has no persistent shell to restart.

Changes

• Implement 1-based inclusive read line ranges, including EOF, inverted, and invalid-input behavior.
• Prove persisted large results can be inspected by line range.
• Stop advertising the unsupported bash restart field.
• Record the public Agent Toolset influence and Mango-specific decision in design provenance.

Acceptance criteria

• Ranged reads return only the requested lines.
• Invalid ranges are tool errors rather than panics.
• Large persisted output can be read in bounded line slices.
• Model-visible schemas expose only implemented semantics.

Non-goals

This does not add a persistent shell, change the public HTTP API, or reuse a host-side SDK executor outside the Mango sandbox abstraction.

Verification

• make verify
• make docs-check