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/read.rs

@@ -2,9 +2,15 @@
 
 use anyhow::{Context, Result};
 use serde::Deserialize;
-use serde_json::json;
 
-use super::ToolDef;
+pub fn tool() -> super::Tool {
+    super::Tool {
+        name: "read_file",
+        description: "Read the contents of a file. Returns the file contents with line numbers.",
+        parameters_json: r#"{"type":"object","properties":{"file_path":{"type":"string","description":"Absolute path to the file to read"},"offset":{"type":"integer","description":"Line number to start reading from (1-based)"},"limit":{"type":"integer","description":"Maximum number of lines to read"}},"required":["file_path"]}"#,
+        handler: |_a, v| Box::pin(async move { read_file(&v) }),
+    }
+}
 
 #[derive(Deserialize)]
 struct Args {
@@ -13,57 +19,21 @@ struct Args {
     offset: usize,
     limit: Option<usize>,
 }
-
 fn default_offset() -> usize { 1 }
 
-pub fn tool() -> super::Tool {
-    super::Tool { def: definition(), handler: |_a, v| Box::pin(async move { read_file(&v) }) }
-}
-
-fn definition() -> ToolDef {
-    ToolDef::new(
-        "read_file",
-        "Read the contents of a file. Returns the file contents with line numbers.",
-        json!({
-            "type": "object",
-            "properties": {
-                "file_path": {
-                    "type": "string",
-                    "description": "Absolute path to the file to read"
-                },
-                "offset": {
-                    "type": "integer",
-                    "description": "Line number to start reading from (1-based). Optional."
-                },
-                "limit": {
-                    "type": "integer",
-                    "description": "Maximum number of lines to read. Optional."
-                }
-            },
-            "required": ["file_path"]
-        }),
-    )
-}
-
 fn read_file(args: &serde_json::Value) -> Result<String> {
-    let args: Args = serde_json::from_value(args.clone())
-        .context("invalid read_file arguments")?;
-
-    let content = std::fs::read_to_string(&args.file_path)
-        .with_context(|| format!("Failed to read {}", args.file_path))?;
-
+    let a: Args = serde_json::from_value(args.clone()).context("invalid read_file arguments")?;
+    let content = std::fs::read_to_string(&a.file_path)
+        .with_context(|| format!("Failed to read {}", a.file_path))?;
     let lines: Vec<&str> = content.lines().collect();
-    let offset = args.offset.max(1) - 1;
-    let limit = args.limit.unwrap_or(lines.len());
-
-    let mut output = String::new();
-    for (i, line) in lines.iter().skip(offset).take(limit).enumerate() {
-        output.push_str(&format!("{:>6}\t{}\n", offset + i + 1, line));
+    let start = a.offset.saturating_sub(1);
+    let end = a.limit.map_or(lines.len(), |l| (start + l).min(lines.len()));
+    if start >= lines.len() {
+        return Ok(format!("(file has {} lines, offset {} is past end)", lines.len(), a.offset));
     }
-
-    if output.is_empty() {
-        output = "(empty file)\n".to_string();
+    let mut out = String::new();
+    for (i, line) in lines[start..end].iter().enumerate() {
+        out.push_str(&format!("{}\t{}\n", start + i + 1, line));
     }
-
-    Ok(output)
+    Ok(out)
 }