refactor(canvas): drop vestigial anti-rewrite prompting from canvas tools

The "do not regenerate wholesale" phrasing in the checkout tool description,
its runtime message, and the generation prompt warned against a workflow a
fresh agent never sees, and could bias against legitimately large rewrites.
The one forward-looking economy nudge (prefer targeted edits over rewriting
the whole file for a small change) stays in the authoring contract in
canvasTemplates.ts, stated once.

Generated-By: PostHog Code
Task-Id: 2b3d176e-3023-41d2-92e8-81eda7c12a8c

Author: adboio

packages/agent/src/adapters/local-tools/tools/canvas.ts

@@ -121,8 +121,8 @@ export const canvasCheckoutTool = defineLocalTool({
   description:
     "Check out a PostHog canvas (a freeform React desktop-fs dashboard) for editing: fetches the live " +
     "source, writes it to a local scratch file, and records the version your edits are based on. " +
-    "Returns the file path. Edit that file with your normal file-editing tools (targeted edits — do not " +
-    "regenerate it wholesale), then call canvas_publish to save. Always start canvas work with this tool.",
+    "Returns the file path. Edit that file with your normal file-editing tools, then call " +
+    "canvas_publish to save. Always start canvas work with this tool.",
   schema: {
     id: z.string().describe("The canvas (desktop-fs dashboard row) id."),
   },
@@ -143,7 +143,7 @@ export const canvasCheckoutTool = defineLocalTool({
       const text = code
         ? `Checked out canvas "${entry.path}" to ${file} (${lines} lines, base version ${
             entry.meta?.currentVersionId ?? "none"
-          }).\nApply your changes by EDITING that file (targeted edits), then call canvas_publish with id "${args.id}".`
+          }).\nApply your changes by editing that file, then call canvas_publish with id "${args.id}".`
         : `Canvas "${entry.path}" is empty. Author the complete single-file React app at ${file}, then call canvas_publish with id "${args.id}".`;
       return { content: [{ type: "text", text }] };
     } catch (err) {

packages/ui/src/features/canvas/freeformPrompt.test.ts

@@ -50,7 +50,7 @@ describe("buildFreeformGenerationPrompt", () => {
     // the live code tool-side and the agent edits the scratch file in place.
     expect(extracted?.body).not.toContain("export const App = () => null;");
     expect(extracted?.body).toContain("canvas_checkout");
-    expect(extracted?.body).toContain("TARGETED edits");
+    expect(extracted?.body).toContain("editing that file");
     // The stale-publish recovery loop is spelled out.
     expect(extracted?.body).toContain("version-conflict");
   });

packages/ui/src/features/canvas/freeformPrompt.ts

@@ -58,9 +58,8 @@ source to a local scratch file and returns the path.`;
 
   const editStep = isEdit
     ? `
-Then apply the user's request by EDITING that file with your file-editing
-tools. Make TARGETED edits — do not rewrite the whole file for a small change,
-and do not paste the source into chat.
+Then apply the user's request by editing that file with your file-editing
+tools. Do not paste the source into chat.
 `
     : "";