tools: static string definitions, no runtime JSON construction

Tool definitions are now &'static str (name, description,
parameters_json) instead of runtime-constructed serde_json::Value.
No more json!() macro, no more ToolDef::new() for tool definitions.

The JSON schema strings are written directly as string literals.
When sent to the API, they can be interpolated without
serialization/deserialization.

Multi-tool modules return fixed-size arrays instead of Vecs:
- memory: [Tool; 12], journal: [Tool; 3]
- channels: [Tool; 4]
- control: [Tool; 3]
- web: [Tool; 2]

ToolDef/FunctionDef remain for backward compat (API wire format,
summarize_args) but are no longer used in tool definitions.

Co-Authored-By: Proof of Concept <poc@bcachefs.org>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

src/agent/tools/write.rs

@@ -2,54 +2,25 @@
 
 use anyhow::{Context, Result};
 use serde::Deserialize;
-use serde_json::json;
-use std::path::Path;
-
-use super::ToolDef;
-
-#[derive(Deserialize)]
-struct Args {
-    file_path: String,
-    content: String,
-}
 
 pub fn tool() -> super::Tool {
-    super::Tool { def: definition(), handler: |_a, v| Box::pin(async move { write_file(&v) }) }
+    super::Tool {
+        name: "write_file",
+        description: "Create or overwrite a file with the given content.",
+        parameters_json: r#"{"type":"object","properties":{"file_path":{"type":"string","description":"Absolute path to write"},"content":{"type":"string","description":"File content"}},"required":["file_path","content"]}"#,
+        handler: |_a, v| Box::pin(async move { write_file(&v) }),
+    }
 }
 
-fn definition() -> ToolDef {
-    ToolDef::new(
-        "write_file",
-        "Write content to a file. Creates the file if it doesn't exist, \
-         overwrites if it does. Creates parent directories as needed.",
-        json!({
-            "type": "object",
-            "properties": {
-                "file_path": {
-                    "type": "string",
-                    "description": "Absolute path to the file to write"
-                },
-                "content": {
-                    "type": "string",
-                    "description": "The content to write to the file"
-                }
-            },
-            "required": ["file_path", "content"]
-        }),
-    )
-}
+#[derive(Deserialize)]
+struct Args { file_path: String, content: String }
 
 fn write_file(args: &serde_json::Value) -> Result<String> {
-    let args: Args = serde_json::from_value(args.clone())
-        .context("invalid write_file arguments")?;
-
-    if let Some(parent) = Path::new(&args.file_path).parent() {
-        std::fs::create_dir_all(parent)
-            .with_context(|| format!("Failed to create directories for {}", args.file_path))?;
+    let a: Args = serde_json::from_value(args.clone()).context("invalid write_file arguments")?;
+    if let Some(parent) = std::path::Path::new(&a.file_path).parent() {
+        std::fs::create_dir_all(parent).ok();
     }
-
-    std::fs::write(&args.file_path, &args.content)
-        .with_context(|| format!("Failed to write {}", args.file_path))?;
-
-    Ok(format!("Wrote {} lines to {}", args.content.lines().count(), args.file_path))
+    std::fs::write(&a.file_path, &a.content)
+        .with_context(|| format!("Failed to write {}", a.file_path))?;
+    Ok(format!("Wrote {} bytes to {}", a.content.len(), a.file_path))
 }