feat(notifications): add notifySubagents toggle to suppress subagent turn pings

A parent agent that spawns 8 subagents was producing 9 "Turn complete"
notifications per round — almost always noise. New `notifySubagents`
config flag (defaults to false) gates `turn-completed` and `turn-error`
from any tab with a `parentTabId`. The flag is intentionally NOT applied
to `permission-required` — a subagent's permission prompt still needs a
human tap to proceed, so suppressing it would silently hang the
subagent. `agent-spawned` is already top-level-only by construction.

Wiring:
- core/notifications/types.ts: NtfyConfig.notifySubagents: boolean
- core/notifications/config.ts: defaults to false; normalize() tolerates
  missing / wrong-typed values and falls back to false
- core/notifications/dispatcher.ts: new optional TabParentLookup option
  (getTabParentId). When notifySubagents=false AND the lookup returns a
  non-empty parent id string, turn-completed/turn-error are dropped.
  Lookup failures (no lookup configured, throws, returns undefined) fall
  back to "treat as top-level" so legitimate top-level events are never
  silently dropped when the DB is briefly unreadable.
- api/app.ts: wires getTabParentId via core's getTab(id)?.parentTabId
- frontend SettingsPanel.svelte: "Include subagent tabs" checkbox with
  an explanatory hint that permission prompts still fire

Tests (+9):
- 3 in config.test.ts: default-false, explicit-true, wrong-typed fallback
- 6 in dispatcher.test.ts: suppression of turn-completed/turn-error from
  subagents, no suppression when flag is true, permission-required not
  gated, graceful fallback when lookup is missing/throws/returns undefined

Live ntfy.sh round-trip re-verified (status: 200).

1 files changed, 17 insertions, 0 deletions

diff --git a/packages/frontend/src/lib/components/SettingsPanel.svelte b/packages/frontend/src/lib/components/SettingsPanel.svelte
index 8031500..08e86ac 100644
--- a/packages/frontend/src/lib/components/SettingsPanel.svelte
+++ b/packages/frontend/src/lib/components/SettingsPanel.svelte
@@ -36,6 +36,7 @@ interface NtfyConfigView {
 	authToken: string;
 	hasAuthToken?: boolean;
 	events: Record<NotificationEventType, boolean>;
+	notifySubagents: boolean;
 }
 
 const NTFY_EVENT_LABELS: Record<NotificationEventType, string> = {
@@ -56,6 +57,7 @@ const DEFAULT_NTFY: NtfyConfigView = {
 		"permission-required": true,
 		"agent-spawned": false,
 	},
+	notifySubagents: false,
 };
 
 let ntfy = $state<NtfyConfigView>({ ...DEFAULT_NTFY, events: { ...DEFAULT_NTFY.events } });
@@ -162,6 +164,7 @@ async function saveNtfy(): Promise<void> {
 			enabled: ntfy.enabled,
 			topicUrl: ntfy.topicUrl,
 			events: ntfy.events,
+			notifySubagents: ntfy.notifySubagents,
 		};
 		if (ntfyAuthTokenInput !== "") payload.authToken = ntfyAuthTokenInput;
 		const res = await fetch(`${apiBase}/notifications`, {
@@ -469,6 +472,20 @@ $effect(() => {
 			{/each}
 		</div>
 
+		<div class="flex flex-col gap-1 mt-1">
+			<label class="flex items-center gap-2 cursor-pointer">
+				<input
+					type="checkbox"
+					class="checkbox checkbox-sm rounded-sm"
+					bind:checked={ntfy.notifySubagents}
+				/>
+				<span class="text-xs text-base-content/70">Include subagent tabs</span>
+			</label>
+			<span class="text-[10px] text-base-content/40 pl-6">
+				Off (default): turn-completed/turn-error from subagents are suppressed. Permission prompts still fire so subagents don't silently hang.
+			</span>
+		</div>
+
 		<div class="flex gap-1 mt-1">
 			<button
 				type="button"