feat(tabs): tab-to-tab agent communication via short handles

Add send_to_tab / read_tab tools so an agent can message or read another
tab by a git-style short handle (shortest unique prefix of the tab UUID,
min 4 chars), shown in the tab bar.

- core/db/tabs: resolveTabPrefix + shortestUniquePrefix (open tabs only,
  LIKE-sanitized prefix matching)
- new tools read-tab.ts / send-to-tab.ts (+ tests) decoupled from the DB
  TabRow via a minimal ResolvedTabRef projection
- agent-manager: unified deliverMessage routing (busy -> queue, idle ->
  new turn) shared by POST /chat and send_to_tab; agent->agent auto-wake
  budget (MAX_AGENT_AUTO_WAKES) to bound ping-pong loops
- summon/loader: send_to_tab + read_tab as grantable tools
- frontend: shortHandleFor + handle badge in TabBar; perm toggles
- notes: tab-comm / user-agents / todo-redesign plans
- chore: biome format fixes (debug-logger, summon.test)

Refs notes/plan-tab-comm.md

1 files changed, 95 insertions, 0 deletions

diff --git a/packages/core/src/tools/read-tab.ts b/packages/core/src/tools/read-tab.ts
new file mode 100644
index 0000000..e80dbd0
--- /dev/null
+++ b/packages/core/src/tools/read-tab.ts
@@ -0,0 +1,95 @@
+import { z } from "zod";
+import type { AgentStatus, ToolDefinition } from "../types/index.js";
+import type { TabResolution } from "./send-to-tab.js";
+
+export interface ReadTabCallbacks {
+	/** Resolve a (possibly short) handle to one open tab. */
+	resolveShortId(prefix: string): TabResolution;
+	/**
+	 * Return the target tab's most recent COMPLETED assistant turn as plain
+	 * text, plus its current status. `text` is null when the tab has no
+	 * completed assistant turn yet.
+	 */
+	getLastResponse(tabId: string): { text: string | null; status: AgentStatus };
+	/** Snapshot of currently-open tabs, for "available tabs" error hints. */
+	listOpenHandles(): Array<{ handle: string; title: string }>;
+}
+
+/** Render the "available tabs" hint shared by the none/ambiguous branches. */
+function renderOpenHandles(handles: Array<{ handle: string; title: string }>): string {
+	if (handles.length === 0) return "No other tabs are currently open.";
+	const lines = handles.map((h) => `  - ${h.handle}: ${h.title}`);
+	return ["Currently open tabs:", ...lines].join("\n");
+}
+
+export function createReadTabTool(callbacks: ReadTabCallbacks): ToolDefinition {
+	return {
+		name: "read_tab",
+		description: [
+			"Read the most recent completed response from another tab (agent) by its short ID.",
+			"",
+			"Returns a SNAPSHOT — it does NOT block or wait for the target to finish.",
+			"  - If the target is idle, you get its just-finished turn.",
+			"  - If the target is still running, you get its PREVIOUS completed turn (if any);",
+			"    call read_tab again later to get the newest one.",
+			"",
+			"Use this after send_to_tab to collect another agent's reply. IDs are git-style",
+			"prefixes: pass any length that uniquely identifies the target (min 4 chars).",
+		].join("\n"),
+		parameters: z.object({
+			tab_id: z
+				.string()
+				.describe(
+					"The short ID (handle) of the tab to read, as shown in the tab bar. Any unique-length prefix works (min 4 chars).",
+				),
+		}),
+		execute: async (args: Record<string, unknown>): Promise<string> => {
+			const rawId = (args.tab_id as string | undefined)?.trim() ?? "";
+
+			if (!rawId) {
+				return `Error: tab_id is required.\n\n${renderOpenHandles(callbacks.listOpenHandles())}`;
+			}
+
+			const resolution = callbacks.resolveShortId(rawId);
+
+			if (resolution.status === "none") {
+				return [
+					`Error: no open tab matches the ID "${rawId}".`,
+					"",
+					renderOpenHandles(callbacks.listOpenHandles()),
+				].join("\n");
+			}
+			if (resolution.status === "ambiguous") {
+				const matches = resolution.matches.map((m) => `  - ${m.handle}: ${m.title}`).join("\n");
+				return [
+					`Error: the ID "${rawId}" is ambiguous — it matches multiple open tabs:`,
+					matches,
+					"",
+					"Add one or more characters to disambiguate.",
+				].join("\n");
+			}
+
+			const target = resolution.tab;
+			const { text, status } = callbacks.getLastResponse(target.id);
+
+			const runningNote =
+				status === "running"
+					? " (this tab is still running; the response below is its previous completed turn — read again later for the newest)"
+					: "";
+
+			if (text === null) {
+				const reason =
+					status === "running"
+						? "it is still working on its first turn"
+						: "it has no assistant responses yet";
+				return `Tab ${target.handle} (${target.title}) has no completed response — ${reason}.`;
+			}
+
+			return [
+				`<tab_response tab="${target.handle}" status="${status}"${runningNote}>`,
+				text,
+				"</tab_response>",
+			].join("\n");
+		},
+	};
+}