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/edit.rs

@@ -8,10 +8,20 @@
 // Supports replace_all for bulk renaming (e.g. variable renames).
 
 use anyhow::{Context, Result};
+use serde::Deserialize;
 use serde_json::json;
 
 use crate::types::ToolDef;
 
+#[derive(Deserialize)]
+struct Args {
+    file_path: String,
+    old_string: String,
+    new_string: String,
+    #[serde(default)]
+    replace_all: bool,
+}
+
 pub fn definition() -> ToolDef {
     ToolDef::new(
         "edit_file",
@@ -44,49 +54,37 @@ pub fn definition() -> ToolDef {
 }
 
 pub fn edit_file(args: &serde_json::Value) -> Result<String> {
-    let path = args["file_path"]
+    let a: Args = serde_json::from_value(args.clone())
-        .as_str()
+        .context("invalid edit_file arguments")?;
-        .context("file_path is required")?;
-    let old_string = args["old_string"]
-        .as_str()
-        .context("old_string is required")?;
-    let new_string = args["new_string"]
-        .as_str()
-        .context("new_string is required")?;
-    let replace_all = args["replace_all"].as_bool().unwrap_or(false);
 
-    if old_string == new_string {
+    if a.old_string == a.new_string {
         anyhow::bail!("old_string and new_string are identical");
     }
 
-    let content =
+    let content = std::fs::read_to_string(&a.file_path)
-        std::fs::read_to_string(path).with_context(|| format!("Failed to read {}", path))?;
+        .with_context(|| format!("Failed to read {}", a.file_path))?;
 
-    if replace_all {
+    let count = content.matches(&*a.old_string).count();
-        let count = content.matches(old_string).count();
+    if count == 0 {
-        if count == 0 {
+        anyhow::bail!("old_string not found in {}", a.file_path);
-            anyhow::bail!("old_string not found in {}", path);
+    }
-        }
+
-        let new_content = content.replace(old_string, new_string);
+    if a.replace_all {
-        std::fs::write(path, &new_content)
+        let new_content = content.replace(&*a.old_string, &a.new_string);
-            .with_context(|| format!("Failed to write {}", path))?;
+        std::fs::write(&a.file_path, &new_content)
-        Ok(format!("Replaced {} occurrences in {}", count, path))
+            .with_context(|| format!("Failed to write {}", a.file_path))?;
+        Ok(format!("Replaced {} occurrences in {}", count, a.file_path))
     } else {
-        let count = content.matches(old_string).count();
-        if count == 0 {
-            anyhow::bail!("old_string not found in {}", path);
-        }
         if count > 1 {
             anyhow::bail!(
                 "old_string appears {} times in {} — use replace_all or provide more context \
                  to make it unique",
-                count,
+                count, a.file_path
-                path
             );
         }
-        let new_content = content.replacen(old_string, new_string, 1);
+        let new_content = content.replacen(&*a.old_string, &a.new_string, 1);
-        std::fs::write(path, &new_content)
+        std::fs::write(&a.file_path, &new_content)
-            .with_context(|| format!("Failed to write {}", path))?;
+            .with_context(|| format!("Failed to write {}", a.file_path))?;
-        Ok(format!("Edited {}", path))
+        Ok(format!("Edited {}", a.file_path))
     }
 }

poc-agent/src/tools/glob_tool.rs

@@ -5,11 +5,21 @@
 // what you want when exploring a codebase.
 
 use anyhow::{Context, Result};
+use serde::Deserialize;
 use serde_json::json;
 use std::path::PathBuf;
 
 use crate::types::ToolDef;
 
+#[derive(Deserialize)]
+struct Args {
+    pattern: String,
+    #[serde(default = "default_path")]
+    path: String,
+}
+
+fn default_path() -> String { ".".into() }
+
 pub fn definition() -> ToolDef {
     ToolDef::new(
         "glob",
@@ -34,14 +44,13 @@ pub fn definition() -> ToolDef {
 }
 
 pub fn glob_search(args: &serde_json::Value) -> Result<String> {
-    let pattern = args["pattern"].as_str().context("pattern is required")?;
+    let a: Args = serde_json::from_value(args.clone())
-    let base = args["path"].as_str().unwrap_or(".");
+        .context("invalid glob arguments")?;
 
-    // Build the full pattern
+    let full_pattern = if a.pattern.starts_with('/') {
-    let full_pattern = if pattern.starts_with('/') {
+        a.pattern.clone()
-        pattern.to_string()
     } else {
-        format!("{}/{}", base, pattern)
+        format!("{}/{}", a.path, a.pattern)
     };
 
     let mut entries: Vec<(PathBuf, std::time::SystemTime)> = Vec::new();

poc-agent/src/tools/read.rs

@@ -1,10 +1,21 @@
 // tools/read.rs — Read file contents
 
 use anyhow::{Context, Result};
+use serde::Deserialize;
 use serde_json::json;
 
 use crate::types::ToolDef;
 
+#[derive(Deserialize)]
+struct Args {
+    file_path: String,
+    #[serde(default = "default_offset")]
+    offset: usize,
+    limit: Option<usize>,
+}
+
+fn default_offset() -> usize { 1 }
+
 pub fn definition() -> ToolDef {
     ToolDef::new(
         "read_file",
@@ -31,21 +42,19 @@ pub fn definition() -> ToolDef {
 }
 
 pub fn read_file(args: &serde_json::Value) -> Result<String> {
-    let path = args["file_path"]
+    let args: Args = serde_json::from_value(args.clone())
-        .as_str()
+        .context("invalid read_file arguments")?;
-        .context("file_path is required")?;
 
-    let content =
+    let content = std::fs::read_to_string(&args.file_path)
-        std::fs::read_to_string(path).with_context(|| format!("Failed to read {}", path))?;
+        .with_context(|| format!("Failed to read {}", args.file_path))?;
 
     let lines: Vec<&str> = content.lines().collect();
-    let offset = args["offset"].as_u64().unwrap_or(1).max(1) as usize - 1;
+    let offset = args.offset.max(1) - 1;
-    let limit = args["limit"].as_u64().unwrap_or(lines.len() as u64) as usize;
+    let limit = args.limit.unwrap_or(lines.len());
 
     let mut output = String::new();
     for (i, line) in lines.iter().skip(offset).take(limit).enumerate() {
-        let line_num = offset + i + 1;
+        output.push_str(&format!("{:>6}\t{}\n", offset + i + 1, line));
-        output.push_str(&format!("{:>6}\t{}\n", line_num, line));
     }
 
     if output.is_empty() {

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"]
+    let args: Args = serde_json::from_value(args.clone())
-        .as_str()
+        .context("invalid write_file arguments")?;
-        .context("file_path is required")?;
-    let content = args["content"].as_str().context("content is required")?;
 
-    // Create parent directories if needed
+    if let Some(parent) = Path::new(&args.file_path).parent() {
-    if let Some(parent) = Path::new(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 {}", args.content.lines().count(), args.file_path))
-    Ok(format!("Wrote {} lines to {}", line_count, path))
 }