diff --git a/apps/desktop/scripts/run-tests.mjs b/apps/desktop/scripts/run-tests.mjs
index d5fd2311..bf148d92 100644
--- a/apps/desktop/scripts/run-tests.mjs
+++ b/apps/desktop/scripts/run-tests.mjs
@@ -48,6 +48,7 @@ const behaviorTests = [
   ".test-dist/tests/agent-setup-support.test.js",
   ".test-dist/tests/plugin-config.test.js",
   ".test-dist/tests/plugin-sdk-bridge.test.js",
+  ".test-dist/tests/plugin-sdk-runtime-helpers.test.js",
   ".test-dist/tests/plugin-sdk-surface-boundaries.test.js",
   ".test-dist/tests/plugin-state.test.js",
   ".test-dist/tests/plugin-runtime.test.js",
diff --git a/apps/desktop/src/check-packaging-contract.ts b/apps/desktop/src/check-packaging-contract.ts
index 36f2cee0..200dd9ed 100644
--- a/apps/desktop/src/check-packaging-contract.ts
+++ b/apps/desktop/src/check-packaging-contract.ts
@@ -118,6 +118,8 @@ const agentSetupSource = readFileSync(join(appDir, "src", "agent-setup.ts"), "ut
 const agentSetupCommandContextSource = readFileSync(join(appDir, "src", "agent-setup-command-context.ts"), "utf8");
 const agentSetupEditorToolsSource = readFileSync(join(appDir, "src", "agent-setup-editor-tools.ts"), "utf8");
 const agentSetupSupportSource = readFileSync(join(appDir, "src", "agent-setup-support.ts"), "utf8");
+const pluginSdkBridgeSource = readFileSync(join(appDir, "src", "plugin-sdk-bridge.ts"), "utf8");
+const pluginSdkRuntimeHelpersSource = readFileSync(join(appDir, "src", "plugin-sdk-runtime-helpers.ts"), "utf8");
 const pluginServiceSource = readFileSync(join(appDir, "src", "plugin-service.ts"), "utf8");
 const pluginServiceDefaultPetSource = readFileSync(join(appDir, "src", "plugin-service-default-pet.ts"), "utf8");
 const pluginServiceSnapshotSource = readFileSync(join(appDir, "src", "plugin-service-snapshot.ts"), "utf8");
@@ -274,6 +276,8 @@ assert.match(controlCenterSettingsCombinedSource, /API key or token|OpenAI API k
 assert.match(pluginServiceSource, /from "\.\/plugin-service-default-pet(?:\.js)?"/, "plugin-service must import the extracted default-pet helper seam.");
 assert.match(pluginServiceSource, /from "\.\/plugin-service-snapshot(?:\.js)?"/, "plugin-service must import the extracted snapshot helper seam.");
 assert.match(pluginServiceSource, /from "\.\/plugin-service-text-helpers(?:\.js)?"/, "plugin-service must import the extracted plugin text helper seam.");
+assert.match(pluginSdkBridgeSource, /from "\.\/plugin-sdk-runtime-helpers(?:\.js)?"/, "plugin-sdk-bridge must import the extracted runtime helper seam.");
+assert.match(pluginSdkRuntimeHelpersSource, /export function nextScheduleDelayMs/, "plugin-sdk runtime helper seam must own schedule delay calculation.");
 assert.match(pluginServiceDefaultPetSource, /export async function buildDefaultPetPluginCommands/, "plugin-service default-pet helper must export default familiar command shaping.");
 assert.match(pluginServiceSnapshotSource, /export async function buildSafePluginRecord/, "plugin-service snapshot helper must export safe plugin snapshot shaping.");
 assert.match(pluginServiceSnapshotSource, /export function validatePluginServiceConfigReplacement/, "plugin-service snapshot helper must export config validation delegation.");
diff --git a/apps/desktop/src/codemap.md b/apps/desktop/src/codemap.md
index 7e3e2576..6b1df38c 100644
--- a/apps/desktop/src/codemap.md
+++ b/apps/desktop/src/codemap.md
@@ -120,7 +120,7 @@ main.ts → initializePluginService(userData, defaultPluginPetApi, appVersion, E
 ├── plugin-runtime.ts reloads enabled manifests
 │   ├── declarative runtime schedules timer triggers
 │   ├── plugin-js-host.ts starts hidden sandboxed BrowserWindow hosts for JavaScript plugins
-│   └── plugin-sdk-bridge.ts → plugin-familiar-api.ts/default-familiar-controller plus schedules, storage, commands, status, logs, and restricted network
+│   └── plugin-sdk-bridge.ts → plugin-sdk-runtime-helpers.ts plus plugin-familiar-api.ts/default-familiar-controller for schedules, storage, commands, status, logs, and restricted network
 ├── plugin-service.ts orchestrates UI actions, permission confirmation, config validation, install/update/uninstall/load-local, and runtime reloads
 └── lifecycle.ts → stopPluginService() on quit
 
@@ -231,7 +231,8 @@ plugin-local-loader.ts validates selected folder manifest and snapshots only fam
 - `plugin-package.ts`: Catalog plugin package download/install with HTTPS host/path allowlist, SHA-256 verification, ZIP size/entry restrictions, manifest/catalog consistency checks, and safe uninstall path resolution.
 - `plugin-local-loader.ts`: Developer loader that validates a selected local folder and snapshots only the manifest into `plugins-dev` with symlink/path/size protections.
 - `plugin-js-host.ts`: Sandboxed hidden BrowserWindow host for JavaScript plugin entry modules with per-plugin session partitioning, navigation/window-open hardening, SDK IPC tokening, registration handshake, config listener cleanup, and teardown.
-- `plugin-sdk-bridge.ts`: Permission-checked JavaScript plugin SDK for familiar speech/reactions, one-shot/repeating/daily schedules, storage with quotas, config listeners, commands, status, logs, and HTTPS-only public-host fetch.
+- `plugin-sdk-bridge.ts`: Permission-checked JavaScript plugin SDK for familiar speech/reactions, storage with quotas, config listeners, commands, status, logs, and HTTPS-only public-host fetch.
+- `plugin-sdk-runtime-helpers.ts`: Extracted schedule timing, timeout wrapping, bubble counting, and callback error normalization helpers for the JavaScript plugin SDK bridge.
 
 **Agent Integration**:
 - `agent-setup.ts`: Claude detection, MCP configuration orchestration, hooks management, action journaling
diff --git a/apps/desktop/src/plugin-sdk-bridge.ts b/apps/desktop/src/plugin-sdk-bridge.ts
index 26c08219..911579d8 100644
--- a/apps/desktop/src/plugin-sdk-bridge.ts
+++ b/apps/desktop/src/plugin-sdk-bridge.ts
@@ -24,6 +24,13 @@ import {
   validateNetOptions,
 } from "./plugin-sdk-network.js";
 import { pluginSdkQuotas } from "./plugin-sdk-quotas.js";
+import {
+  countActiveBubbles,
+  nextScheduleDelayMs,
+  parseDaily,
+  safeError,
+  withTimeout,
+} from "./plugin-sdk-runtime-helpers.js";
 import {
   createPluginAudioApi,
   createPluginBusApi,
@@ -40,7 +47,6 @@ import {
   commandIdPattern,
   isRecord,
   namedHostIcons,
-  nextCronRunMs,
   normalizeJson,
   parseCronExpression,
   renderLimitedMarkdown,
@@ -681,19 +687,3 @@ export class PluginSdkBridge {
     return state;
   }
 }
-
-function countActiveBubbles(state: PluginRuntimeState): number { return state.bubbles.size; }
-function parseDaily(spec: string | { time: string; days?: number[] }): { time: string; days?: number[] } { const value = typeof spec === "string" ? { time: spec } : spec; const m = /^(\d{2}):(\d{2})$/.exec(value.time); if (!m || Number(m[1]) > 23 || Number(m[2]) > 59) throw new Error("Daily schedule time must be HH:mm between 00:00 and 23:59."); if (value.days && (!Array.isArray(value.days) || value.days.some((d) => !Number.isInteger(d) || d < 0 || d > 6))) throw new Error("Daily schedule days must be weekdays 0-6."); return value; }
-function msUntilDaily(spec: { time: string; days?: number[] }): number { const [hour, minute] = spec.time.split(":").map(Number); const now = new Date(); for (let add = 0; add <= 7; add += 1) { const next = new Date(now); next.setDate(now.getDate() + add); next.setHours(hour ?? 0, minute ?? 0, 0, 0); if (next > now && (!spec.days || spec.days.includes(next.getDay()))) return next.getTime() - now.getTime(); } return 24 * 60 * 60 * 1000; }
-
-function nextScheduleDelayMs(spec: ScheduleSpec): number | null {
-  if (spec.type === "once") return Math.max(1, spec.delayMs);
-  if (spec.type === "every") return Math.max(1, spec.intervalMs);
-  if (spec.type === "daily") return msUntilDaily(spec.daily);
-  if (spec.type === "at") return Math.max(1_000, spec.timestamp - Date.now());
-  const next = nextCronRunMs(spec.expr, Date.now());
-  return next === null ? null : Math.max(1_000, next - Date.now());
-}
-
-function withTimeout<T>(promise: Promise<T>, timeoutMs: number): Promise<T> { return new Promise((resolve, reject) => { const timeout = setTimeout(() => reject(new Error("Plugin command timed out.")), timeoutMs); promise.then((v) => { clearTimeout(timeout); resolve(v); }, (e) => { clearTimeout(timeout); reject(e); }); }); }
-function safeError(error: unknown): string { return error instanceof Error ? error.message : "Plugin SDK callback failed."; }
diff --git a/apps/desktop/src/plugin-sdk-runtime-helpers.ts b/apps/desktop/src/plugin-sdk-runtime-helpers.ts
new file mode 100644
index 00000000..84fd6fdb
--- /dev/null
+++ b/apps/desktop/src/plugin-sdk-runtime-helpers.ts
@@ -0,0 +1,61 @@
+import type { PluginRuntimeState, ScheduleSpec } from "./plugin-sdk-state.js";
+import { nextCronRunMs } from "./plugin-sdk-validators.js";
+
+export function countActiveBubbles(state: PluginRuntimeState): number {
+  return state.bubbles.size;
+}
+
+export function parseDaily(spec: string | { time: string; days?: number[] }): { time: string; days?: number[] } {
+  const value = typeof spec === "string" ? { time: spec } : spec;
+  const match = /^(\d{2}):(\d{2})$/.exec(value.time);
+  if (!match || Number(match[1]) > 23 || Number(match[2]) > 59) {
+    throw new Error("Daily schedule time must be HH:mm between 00:00 and 23:59.");
+  }
+  if (value.days && (!Array.isArray(value.days) || value.days.some((day) => !Number.isInteger(day) || day < 0 || day > 6))) {
+    throw new Error("Daily schedule days must be weekdays 0-6.");
+  }
+  return value;
+}
+
+export function nextScheduleDelayMs(spec: ScheduleSpec): number | null {
+  if (spec.type === "once") return Math.max(1, spec.delayMs);
+  if (spec.type === "every") return Math.max(1, spec.intervalMs);
+  if (spec.type === "daily") return msUntilDaily(spec.daily);
+  if (spec.type === "at") return Math.max(1_000, spec.timestamp - Date.now());
+  const next = nextCronRunMs(spec.expr, Date.now());
+  return next === null ? null : Math.max(1_000, next - Date.now());
+}
+
+export function withTimeout<T>(promise: Promise<T>, timeoutMs: number): Promise<T> {
+  return new Promise((resolve, reject) => {
+    const timeout = setTimeout(() => reject(new Error("Plugin command timed out.")), timeoutMs);
+    promise.then(
+      (value) => {
+        clearTimeout(timeout);
+        resolve(value);
+      },
+      (error) => {
+        clearTimeout(timeout);
+        reject(error);
+      },
+    );
+  });
+}
+
+export function safeError(error: unknown): string {
+  return error instanceof Error ? error.message : "Plugin SDK callback failed.";
+}
+
+function msUntilDaily(spec: { time: string; days?: number[] }): number {
+  const [hour, minute] = spec.time.split(":").map(Number);
+  const now = new Date();
+  for (let add = 0; add <= 7; add += 1) {
+    const next = new Date(now);
+    next.setDate(now.getDate() + add);
+    next.setHours(hour ?? 0, minute ?? 0, 0, 0);
+    if (next > now && (!spec.days || spec.days.includes(next.getDay()))) {
+      return next.getTime() - now.getTime();
+    }
+  }
+  return 24 * 60 * 60 * 1000;
+}
diff --git a/apps/desktop/tests/plugin-sdk-runtime-helpers.test.ts b/apps/desktop/tests/plugin-sdk-runtime-helpers.test.ts
new file mode 100644
index 00000000..a8dacd17
--- /dev/null
+++ b/apps/desktop/tests/plugin-sdk-runtime-helpers.test.ts
@@ -0,0 +1,32 @@
+import assert from "node:assert/strict";
+import { readFileSync } from "node:fs";
+import { dirname, resolve } from "node:path";
+import { fileURLToPath } from "node:url";
+
+import { countActiveBubbles, nextScheduleDelayMs, parseDaily, safeError, withTimeout } from "../src/plugin-sdk-runtime-helpers.js";
+
+const desktopRoot = process.env.FAMILIAROS_DESKTOP_ROOT ?? resolve(dirname(fileURLToPath(import.meta.url)), "..");
+const pluginSdkBridgeSource = readFileSync(resolve(desktopRoot, "src/plugin-sdk-bridge.ts"), "utf8");
+const pluginSdkRuntimeHelpersSource = readFileSync(resolve(desktopRoot, "src/plugin-sdk-runtime-helpers.ts"), "utf8");
+
+assert.match(pluginSdkBridgeSource, /from "\.\/plugin-sdk-runtime-helpers\.js"/, "Plugin SDK bridge must import the extracted runtime helper seam.");
+assert.match(pluginSdkRuntimeHelpersSource, /export function nextScheduleDelayMs/, "Plugin SDK runtime helpers must export schedule delay calculation.");
+assert.match(pluginSdkRuntimeHelpersSource, /export function withTimeout/, "Plugin SDK runtime helpers must export timeout wrapping.");
+
+assert.deepEqual(parseDaily("09:15"), { time: "09:15" });
+assert.deepEqual(parseDaily({ time: "18:45", days: [1, 3, 5] }), { time: "18:45", days: [1, 3, 5] });
+assert.throws(() => parseDaily("25:00"), /Daily schedule time must be HH:mm/);
+assert.throws(() => parseDaily({ time: "12:30", days: [7] }), /Daily schedule days must be weekdays 0-6/);
+
+assert.equal(nextScheduleDelayMs({ type: "once", delayMs: 0 }), 1);
+assert.equal(nextScheduleDelayMs({ type: "every", intervalMs: 25 }), 25);
+assert.equal(nextScheduleDelayMs({ type: "at", timestamp: Date.now() - 5_000 }), 1_000);
+
+assert.equal(safeError(new Error("boom")), "boom");
+assert.equal(safeError("boom"), "Plugin SDK callback failed.");
+assert.equal(countActiveBubbles({ bubbles: new Map([["one", {}], ["two", {}]]) } as never), 2);
+
+await assert.rejects(() => withTimeout(new Promise(() => undefined), 5), /Plugin command timed out\./);
+await assert.doesNotReject(() => withTimeout(Promise.resolve("ok"), 50));
+
+console.error("Plugin SDK runtime helper validation passed.");