diff --git a/scripts/lib/extension-test-plan.mjs b/scripts/lib/extension-test-plan.mjs
index 1369b06df5c..8b9d74589ca 100644
--- a/scripts/lib/extension-test-plan.mjs
+++ b/scripts/lib/extension-test-plan.mjs
@@ -30,8 +30,28 @@ import { listAvailableExtensionIds } from "./changed-extensions.mjs";
 const repoRoot = path.resolve(import.meta.dirname, "..", "..");
 export const DEFAULT_EXTENSION_TEST_SHARD_COUNT = 6;
 const EXTENSION_TEST_COST_MULTIPLIERS = {
-  "test/vitest/vitest.extension-feishu.config.ts": 1.6,
-  "test/vitest/vitest.extension-msteams.config.ts": 1.6,
+  // CI shard planning uses measured wall time rather than raw file count.
+  // Import-heavy channel suites vary widely: Slack/Mattermost are much more
+  // expensive per file than Matrix/Discord/MSTeams.
+  "test/vitest/vitest.extension-bluebubbles.config.ts": 0.8,
+  "test/vitest/vitest.extension-browser.config.ts": 0.55,
+  "test/vitest/vitest.extension-discord.config.ts": 0.3,
+  "test/vitest/vitest.extension-feishu.config.ts": 0.6,
+  "test/vitest/vitest.extension-imessage.config.ts": 0.9,
+  "test/vitest/vitest.extension-matrix.config.ts": 0.25,
+  "test/vitest/vitest.extension-mattermost.config.ts": 1.05,
+  "test/vitest/vitest.extension-media.config.ts": 0.7,
+  "test/vitest/vitest.extension-memory.config.ts": 0.3,
+  "test/vitest/vitest.extension-messaging.config.ts": 0.4,
+  "test/vitest/vitest.extension-misc.config.ts": 0.7,
+  "test/vitest/vitest.extension-msteams.config.ts": 0.3,
+  "test/vitest/vitest.extension-providers.config.ts": 0.5,
+  "test/vitest/vitest.extension-qa.config.ts": 0.4,
+  "test/vitest/vitest.extension-slack.config.ts": 0.7,
+  "test/vitest/vitest.extension-telegram.config.ts": 0.4,
+  "test/vitest/vitest.extension-voice-call.config.ts": 0.25,
+  "test/vitest/vitest.extension-whatsapp.config.ts": 0.6,
+  "test/vitest/vitest.extension-zalo.config.ts": 0.7,
   // This shared config is comparatively cheap per file, so raw file count
   // overstates its real wall-clock cost during CI shard planning.
   "test/vitest/vitest.extensions.config.ts": 0.45,
diff --git a/test/scripts/test-extension.test.ts b/test/scripts/test-extension.test.ts
index 0853c97eaf0..6ed409aee7f 100644
--- a/test/scripts/test-extension.test.ts
+++ b/test/scripts/test-extension.test.ts
@@ -476,10 +476,22 @@ describe("scripts/test-extension.mjs", () => {
 
     const msTeamsShardIndex = shards.findIndex((shard) => shard.extensionIds.includes("msteams"));
     const feishuShardIndex = shards.findIndex((shard) => shard.extensionIds.includes("feishu"));
+    const browserShardIndex = shards.findIndex((shard) => shard.extensionIds.includes("browser"));
+    const slackShardIndex = shards.findIndex((shard) => shard.extensionIds.includes("slack"));
+    const matrixShardIndex = shards.findIndex((shard) => shard.extensionIds.includes("matrix"));
+    const mattermostShardIndex = shards.findIndex((shard) =>
+      shard.extensionIds.includes("mattermost"),
+    );
 
     expect(msTeamsShardIndex).toBeGreaterThanOrEqual(0);
     expect(feishuShardIndex).toBeGreaterThanOrEqual(0);
     expect(msTeamsShardIndex).not.toBe(feishuShardIndex);
+    expect(browserShardIndex).toBeGreaterThanOrEqual(0);
+    expect(slackShardIndex).toBeGreaterThanOrEqual(0);
+    expect(browserShardIndex).not.toBe(slackShardIndex);
+    expect(matrixShardIndex).toBeGreaterThanOrEqual(0);
+    expect(mattermostShardIndex).toBeGreaterThanOrEqual(0);
+    expect(matrixShardIndex).not.toBe(mattermostShardIndex);
   });
 
   it("runs extension batch config groups concurrently when requested", async () => {