refactor: use typed Deserialize structs for tool arguments

Convert read_file, write_file, edit_file, and glob from manual
args["key"].as_str() parsing to serde_json::from_value with typed
Args structs. Gives type safety, default values via serde attributes,
and clearer error messages on missing/wrong-type arguments.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

poc-agent/src/tools/write.rs

@@ -1,11 +1,18 @@
 // tools/write.rs — Write file contents
 
 use anyhow::{Context, Result};
+use serde::Deserialize;
 use serde_json::json;
 use std::path::Path;
 
 use crate::types::ToolDef;
 
+#[derive(Deserialize)]
+struct Args {
+    file_path: String,
+    content: String,
+}
+
 pub fn definition() -> ToolDef {
     ToolDef::new(
         "write_file",
@@ -29,19 +36,16 @@ pub fn definition() -> ToolDef {
 }
 
 pub fn write_file(args: &serde_json::Value) -> Result<String> {
-    let path = args["file_path"]
-        .as_str()
-        .context("file_path is required")?;
-    let content = args["content"].as_str().context("content is required")?;
+    let args: Args = serde_json::from_value(args.clone())
+        .context("invalid write_file arguments")?;
 
-    // Create parent directories if needed
-    if let Some(parent) = Path::new(path).parent() {
+    if let Some(parent) = Path::new(&args.file_path).parent() {
         std::fs::create_dir_all(parent)
-            .with_context(|| format!("Failed to create directories for {}", path))?;
+            .with_context(|| format!("Failed to create directories for {}", args.file_path))?;
     }
 
-    std::fs::write(path, content).with_context(|| format!("Failed to write {}", path))?;
+    std::fs::write(&args.file_path, &args.content)
+        .with_context(|| format!("Failed to write {}", args.file_path))?;
 
-    let line_count = content.lines().count();
-    Ok(format!("Wrote {} lines to {}", line_count, path))
+    Ok(format!("Wrote {} lines to {}", args.content.lines().count(), args.file_path))
 }