Revert "Warn when an agent plugin prompt file is missing (#928)"

This reverts commit 9ff51db.

Author: TheGreatAxios

src/plugins/agent-plugins.test.ts

@@ -176,22 +176,4 @@ describe("resolveAgentPluginProfiles", () => {
       ),
     ).toBe(true);
   });
-
-  test("warns once when a prompt file is missing and still loads the profile", async () => {
-    const { mod, config } = agentModule("p1", [
-      { id: "scout", systemPromptPath: "prompts/does-not-exist.md" },
-    ]);
-    mod.dir = "/tmp/wt-cl-6724-missing-prompt-dir";
-    const warnings: string[] = [];
-    const profiles = await resolveAgentPluginProfiles([mod], config, (msg) =>
-      warnings.push(msg),
-    );
-    expect(profiles.length).toBe(1);
-    expect(defined(profiles[0]).systemPromptRole).toBeUndefined();
-    expect(warnings.length).toBe(1);
-    expect(warnings[0]).toContain('"p1"');
-    expect(warnings[0]).toContain('"scout"');
-    expect(warnings[0]).toContain("prompts/does-not-exist.md");
-    expect(defined(warnings[0])).toMatch(/unreadable|missing/i);
-  });
 });

src/plugins/agent-plugins.ts

@@ -90,18 +90,14 @@ export async function resolveAgentPluginProfiles(
         profile.systemPromptRole === undefined &&
         mod.dir !== undefined
       ) {
-        const promptPath = join(mod.dir, profile.systemPromptPath);
         try {
-          const promptRaw = await readFile(promptPath, "utf8");
-          profile.systemPromptRole = promptRaw.trim();
-        } catch (err) {
-          const reason =
-            (err instanceof Error ? err.message : String(err))
-              .split("\n")[0]
-              ?.trim() || "unknown error";
-          onWarning(
-            `plugin "${mod.manifest.id}" agent "${profile.id}" systemPromptPath "${profile.systemPromptPath}" unreadable (${promptPath}): ${reason}`,
+          const promptRaw = await readFile(
+            join(mod.dir, profile.systemPromptPath),
+            "utf8",
           );
+          profile.systemPromptRole = promptRaw.trim();
+        } catch {
+          // Missing prompt file is non-fatal — the profile loads without a role.
         }
       }
       // Provenance for search_agents: Claude marketplace installs stamp