chore: refactor tool handling (#4510)

# Tool System Refactor

- Centralizes tool definitions and execution in `core/src/tools/*`:
specs (`spec.rs`), handlers (`handlers/*`), router (`router.rs`),
registry/dispatch (`registry.rs`), and shared context (`context.rs`).
One registry now builds the model-visible tool list and binds handlers.
- Router converts model responses to tool calls; Registry dispatches
with consistent telemetry via `codex-rs/otel` and unified error
handling. Function, Local Shell, MCP, and experimental `unified_exec`
all flow through this path; legacy shell aliases still work.
- Rationale: reduce per‑tool boilerplate, keep spec/handler in sync, and
make adding tools predictable and testable.

Example: `read_file`
- Spec: `core/src/tools/spec.rs` (see `create_read_file_tool`,
registered by `build_specs`).
- Handler: `core/src/tools/handlers/read_file.rs` (absolute `file_path`,
1‑indexed `offset`, `limit`, `L#: ` prefixes, safe truncation).
- E2E test: `core/tests/suite/read_file.rs` validates the tool returns
the requested lines.

## Next steps:
- Decompose `handle_container_exec_with_params` 
- Add parallel tool calls

codex-rs/otel/src/otel_event_manager.rs

@@ -14,6 +14,7 @@ use eventsource_stream::EventStreamError as StreamError;
 use reqwest::Error;
 use reqwest::Response;
 use serde::Serialize;
+use std::borrow::Cow;
 use std::fmt::Display;
 use std::time::Duration;
 use std::time::Instant;
@@ -366,10 +367,10 @@ impl OtelEventManager {
         call_id: &str,
         arguments: &str,
         f: F,
-    ) -> Result<String, E>
+    ) -> Result<(String, bool), E>
     where
         F: FnOnce() -> Fut,
-        Fut: Future<Output = Result<String, E>>,
+        Fut: Future<Output = Result<(String, bool), E>>,
         E: Display,
     {
         let start = Instant::now();
@@ -377,10 +378,12 @@ impl OtelEventManager {
         let duration = start.elapsed();
 
         let (output, success) = match &result {
-            Ok(content) => (content, true),
-            Err(error) => (&error.to_string(), false),
+            Ok((preview, success)) => (Cow::Borrowed(preview.as_str()), *success),
+            Err(error) => (Cow::Owned(error.to_string()), false),
         };
 
+        let success_str = if success { "true" } else { "false" };
+
         tracing::event!(
             tracing::Level::INFO,
             event.name = "codex.tool_result",
@@ -396,7 +399,8 @@ impl OtelEventManager {
             call_id = %call_id,
             arguments = %arguments,
             duration_ms = %duration.as_millis(),
-            success = %success,
+            success = %success_str,
+            // `output` is truncated by the tool layer before reaching telemetry.
             output = %output,
         );