refactor: dedupe infra lowercase helpers

src/plugin-sdk/boolean-param.ts

@@ -1,3 +1,5 @@
+import { normalizeOptionalLowercaseString } from "../shared/string-coerce.js";
+
 /** Read loose boolean params from tool input that may arrive as booleans or "true"/"false" strings. */
 export function readBooleanParam(
   params: Record<string, unknown>,
@@ -7,14 +9,12 @@ export function readBooleanParam(
   if (typeof raw === "boolean") {
     return raw;
   }
-  if (typeof raw === "string") {
-    const trimmed = raw.trim().toLowerCase();
-    if (trimmed === "true") {
-      return true;
-    }
-    if (trimmed === "false") {
-      return false;
-    }
+  const normalized = normalizeOptionalLowercaseString(raw);
+  if (normalized === "true") {
+    return true;
+  }
+  if (normalized === "false") {
+    return false;
   }
   return undefined;
 }

src/plugin-sdk/webhook-request-guards.ts

@@ -8,6 +8,7 @@ import {
   requestBodyErrorToText,
 } from "../infra/http-body.js";
 import { pruneMapToMaxSize } from "../infra/map-size.js";
+import { normalizeOptionalLowercaseString } from "../shared/string-coerce.js";
 import type { FixedWindowRateLimiter } from "./webhook-memory-guards.js";
 
 export type WebhookBodyReadProfile = "pre-auth" | "post-auth";
@@ -144,7 +145,7 @@ export function isJsonContentType(value: string | string[] | undefined): boolean
   if (!first) {
     return false;
   }
-  const mediaType = first.split(";", 1)[0]?.trim().toLowerCase();
+  const mediaType = normalizeOptionalLowercaseString(first.split(";", 1)[0]);
   return mediaType === "application/json" || Boolean(mediaType?.endsWith("+json"));
 }