Fix coding agent tools to return error content instead of throwing

Tools now resolve with error messages in content blocks rather than
rejecting the promise. This matches the expected behavior where tools
always return a result, with errors indicated in the text content.

- read: Return error content for missing files
- edit: Return error content for missing files, text not found, multiple matches
- bash: Return error content for command failures, timeouts, and aborts
- All tools now include required details field in error results

packages/coding-agent/src/tools/read.ts

@@ -82,7 +82,10 @@ export const readTool: AgentTool<typeof readSchema> = {
 						if (signal) {
 							signal.removeEventListener("abort", onAbort);
 						}
-						reject(new Error(`File not found: ${path}`));
+						resolve({
+							content: [{ type: "text", text: `Error: File not found: ${path}` }],
+							details: undefined,
+						});
 						return;
 					}