fix(exec): honor explicit null node selection

[mikemikimike]

Summary

• honor an explicit node: null as a request to use the local execution path
• preserve configured and provider-selected defaults when node is omitted
• add a regression test with a connected node provider and a configured default

Root cause

ExecTool converted the optional node value to a string and then fell back to the configured or provider default whenever that conversion returned None. This made an explicit JSON null indistinguishable from an omitted field, so a tool call intended to return to the local sandbox continued to execute on the selected SSH node.

Validation

• targeted Rust formatting check for crates/tools/src/exec.rs
• git diff --check
• local test execution was blocked by the pinned nightly toolchain's incomplete installation and an uncached Git submodule dependency; the repository's remote CI is required for compilation and test verification

Closes #1246.

[greptile-apps]

Greptile Summary

The PR now distinguishes an explicitly null node from an omitted value, routing explicit null requests through local execution while preserving configured and provider defaults when omitted.

• Updates the published exec-tool schema to accept both string and null node values.
• Bypasses remote node selection when the caller explicitly supplies node: null.
• Adds regression coverage for local execution and the nullable schema.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

Important Files Changed

Filename	Overview
crates/tools/src/exec.rs	Correctly exposes null in the node schema and treats explicit null as a local-execution override without changing omitted-node behavior.
crates/tools/src/exec/tests.rs	Adds focused regression tests covering explicit-null local routing and the corresponding schema contract.

_{Reviews (2): Last reviewed commit: "fix(exec): allow null node in tool schem..." | Re-trigger Greptile}

[mikemikimike]

fixed-in-7bdc19e

[penso]

@greptileai review