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

5 files changed, 394 insertions, 6 deletions

diff --git a/packages/core/tests/agents/loader.test.ts b/packages/core/tests/agents/loader.test.ts
index 88173ea..35ab0cf 100644
--- a/packages/core/tests/agents/loader.test.ts
+++ b/packages/core/tests/agents/loader.test.ts
@@ -22,10 +22,34 @@ describe("expandAgentToolNames", () => {
 		expect(out).toContain("run_shell");
 	});
 
+	it("passes through the tab tools as independent names (no tab_comm group)", () => {
+		const out = expandAgentToolNames(["send_to_tab", "read_tab"]);
+		expect(out).toContain("send_to_tab");
+		expect(out).toContain("read_tab");
+		// Granting only one must not pull in the other.
+		const onlySend = expandAgentToolNames(["send_to_tab"]);
+		expect(onlySend).toContain("send_to_tab");
+		expect(onlySend).not.toContain("read_tab");
+	});
+
 	it("passes through non-group tool names unchanged", () => {
-		const out = expandAgentToolNames(["summon", "retrieve", "web_search", "youtube_transcribe"]);
+		const out = expandAgentToolNames([
+			"summon",
+			"retrieve",
+			"web_search",
+			"youtube_transcribe",
+			"send_to_tab",
+			"read_tab",
+		]);
 		expect(out).toEqual(
-			expect.arrayContaining(["summon", "retrieve", "web_search", "youtube_transcribe"]),
+			expect.arrayContaining([
+				"summon",
+				"retrieve",
+				"web_search",
+				"youtube_transcribe",
+				"send_to_tab",
+				"read_tab",
+			]),
 		);
 	});
 
diff --git a/packages/core/tests/db/tabs.test.ts b/packages/core/tests/db/tabs.test.ts
index e1c9bf8..67533dc 100644
--- a/packages/core/tests/db/tabs.test.ts
+++ b/packages/core/tests/db/tabs.test.ts
@@ -73,6 +73,22 @@ class FakeDatabase {
 			return [{ max_pos: maxPos }];
 		}
 
+		// resolveTabPrefix: open tabs whose id starts with a sanitized prefix.
+		// The production query binds `$prefix` as `<sanitized>%`; emulate SQLite
+		// LIKE prefix semantics here (case-insensitive, `%` = "rest of string").
+		if (norm === "SELECT * FROM tabs WHERE is_open = 1 AND id LIKE $prefix ORDER BY position ASC") {
+			const raw = String(params?.$prefix ?? "");
+			const needle = raw.endsWith("%") ? raw.slice(0, -1) : raw;
+			return this.rows
+				.filter((r) => r.is_open === 1 && r.id.toLowerCase().startsWith(needle.toLowerCase()))
+				.sort((a, b) => a.position - b.position);
+		}
+
+		// shortestUniquePrefix: all open tab ids.
+		if (norm === "SELECT id FROM tabs WHERE is_open = 1") {
+			return this.rows.filter((r) => r.is_open === 1).map((r) => ({ id: r.id }));
+		}
+
 		throw new Error(`FakeDatabase: unsupported SELECT: ${norm}`);
 	}
 
@@ -134,7 +150,8 @@ vi.mock("../../src/db/index.js", () => ({
 // Dynamic import AFTER `vi.mock` registers (vitest hoists `vi.mock` to
 // the very top of the file, so by the time this line runs the mock is
 // active for `./index.js` resolution inside `tabs.ts`).
-const { archiveTab, createTab, getDescendantIds, getTab } = await import("../../src/db/tabs.js");
+const { archiveTab, createTab, getDescendantIds, getTab, resolveTabPrefix, shortestUniquePrefix } =
+	await import("../../src/db/tabs.js");
 
 beforeAll(() => {
 	fakeDb = new FakeDatabase();
@@ -234,3 +251,103 @@ describe("getDescendantIds", () => {
 		expect(ids2).toEqual(["b1", "a1"]);
 	});
 });
+
+// ---------------------------------------------------------------------------
+// resolveTabPrefix — git-style short-handle resolution
+// ---------------------------------------------------------------------------
+describe("resolveTabPrefix", () => {
+	it("returns none when the prefix is shorter than the minimum length", () => {
+		createTab("abcd1234-0000-4000-8000-000000000000", "A");
+		// 3 chars < MIN_TAB_PREFIX_LENGTH (4)
+		expect(resolveTabPrefix("abc").status).toBe("none");
+	});
+
+	it("returns none when no open tab matches", () => {
+		createTab("abcd1234-0000-4000-8000-000000000000", "A");
+		expect(resolveTabPrefix("ffff").status).toBe("none");
+	});
+
+	it("resolves a unique 4-char prefix to the single matching tab", () => {
+		createTab("abcd1234-0000-4000-8000-000000000000", "Alpha");
+		createTab("9999aaaa-0000-4000-8000-000000000000", "Beta");
+		const res = resolveTabPrefix("abcd");
+		expect(res.status).toBe("ok");
+		if (res.status === "ok") {
+			expect(res.tab.id).toBe("abcd1234-0000-4000-8000-000000000000");
+			expect(res.tab.title).toBe("Alpha");
+		}
+	});
+
+	it("resolves the full UUID (a maximal prefix)", () => {
+		createTab("abcd1234-0000-4000-8000-000000000000", "Alpha");
+		const res = resolveTabPrefix("abcd1234-0000-4000-8000-000000000000");
+		expect(res.status).toBe("ok");
+	});
+
+	it("reports ambiguity when multiple open tabs share the prefix", () => {
+		createTab("abcd1111-0000-4000-8000-000000000000", "One");
+		createTab("abcd2222-0000-4000-8000-000000000000", "Two");
+		const res = resolveTabPrefix("abcd");
+		expect(res.status).toBe("ambiguous");
+		if (res.status === "ambiguous") {
+			expect(res.matches).toHaveLength(2);
+			expect(res.matches.map((m) => m.title).sort()).toEqual(["One", "Two"]);
+		}
+	});
+
+	it("disambiguates when one more character is supplied", () => {
+		createTab("abcd1111-0000-4000-8000-000000000000", "One");
+		createTab("abcd2222-0000-4000-8000-000000000000", "Two");
+		const res = resolveTabPrefix("abcd1");
+		expect(res.status).toBe("ok");
+		if (res.status === "ok") expect(res.tab.title).toBe("One");
+	});
+
+	it("matches case-insensitively (UUIDs are lowercase; LIKE is ASCII-CI)", () => {
+		createTab("abcd1234-0000-4000-8000-000000000000", "Alpha");
+		const res = resolveTabPrefix("ABCD");
+		expect(res.status).toBe("ok");
+	});
+
+	it("sanitizes LIKE wildcards so they cannot broaden the match", () => {
+		createTab("abcd1234-0000-4000-8000-000000000000", "Alpha");
+		createTab("9999aaaa-0000-4000-8000-000000000000", "Beta");
+		// `%` would match everything if not stripped; after sanitization the
+		// query is effectively `abcd%` which matches only Alpha.
+		const res = resolveTabPrefix("ab%d");
+		// "ab%d" -> sanitized "abd" (3 chars) -> below min length -> none.
+		expect(res.status).toBe("none");
+	});
+
+	it("excludes archived (closed) tabs from matches", () => {
+		createTab("abcd1234-0000-4000-8000-000000000000", "Alpha");
+		archiveTab("abcd1234-0000-4000-8000-000000000000");
+		expect(resolveTabPrefix("abcd").status).toBe("none");
+	});
+});
+
+// ---------------------------------------------------------------------------
+// shortestUniquePrefix — display-handle derivation
+// ---------------------------------------------------------------------------
+describe("shortestUniquePrefix", () => {
+	it("returns a 4-char prefix when no other open tab collides", () => {
+		createTab("abcd1234-0000-4000-8000-000000000000", "Alpha");
+		expect(shortestUniquePrefix("abcd1234-0000-4000-8000-000000000000")).toBe("abcd");
+	});
+
+	it("grows the prefix one char at a time on a collision", () => {
+		createTab("abcd1111-0000-4000-8000-000000000000", "One");
+		createTab("abcd2222-0000-4000-8000-000000000000", "Two");
+		// First differing char is at index 4, so a 5-char prefix is unique.
+		expect(shortestUniquePrefix("abcd1111-0000-4000-8000-000000000000")).toBe("abcd1");
+		expect(shortestUniquePrefix("abcd2222-0000-4000-8000-000000000000")).toBe("abcd2");
+	});
+
+	it("ignores closed tabs when computing uniqueness", () => {
+		createTab("abcd1111-0000-4000-8000-000000000000", "One");
+		createTab("abcd2222-0000-4000-8000-000000000000", "Two");
+		archiveTab("abcd2222-0000-4000-8000-000000000000");
+		// With Two closed, One no longer collides → back to 4 chars.
+		expect(shortestUniquePrefix("abcd1111-0000-4000-8000-000000000000")).toBe("abcd");
+	});
+});
diff --git a/packages/core/tests/tools/read-tab.test.ts b/packages/core/tests/tools/read-tab.test.ts
new file mode 100644
index 0000000..71e419c
--- /dev/null
+++ b/packages/core/tests/tools/read-tab.test.ts
@@ -0,0 +1,101 @@
+import { describe, expect, it } from "vitest";
+import { createReadTabTool, type ReadTabCallbacks } from "../../src/tools/read-tab.js";
+import type { TabResolution } from "../../src/tools/send-to-tab.js";
+
+function makeCallbacks(overrides: Partial<ReadTabCallbacks> = {}): ReadTabCallbacks {
+	return {
+		resolveShortId: (): TabResolution => ({
+			status: "ok",
+			tab: { id: "target-id", title: "Target", handle: "targ" },
+		}),
+		getLastResponse: () => ({ text: "the answer is 42", status: "idle" }),
+		listOpenHandles: () => [{ handle: "targ", title: "Target" }],
+		...overrides,
+	};
+}
+
+describe("createReadTabTool — schema & description", () => {
+	it("is a non-blocking snapshot read", () => {
+		const tool = createReadTabTool(makeCallbacks());
+		expect(tool.name).toBe("read_tab");
+		expect(tool.description).toContain("SNAPSHOT");
+		expect(tool.description.toLowerCase()).toContain("does not block");
+	});
+});
+
+describe("createReadTabTool — execute()", () => {
+	it("returns the last assistant response wrapped in a tab_response tag", async () => {
+		const tool = createReadTabTool(makeCallbacks());
+		const out = await tool.execute({ tab_id: "targ" });
+		expect(out).toContain("<tab_response");
+		expect(out).toContain('tab="targ"');
+		expect(out).toContain('status="idle"');
+		expect(out).toContain("the answer is 42");
+		expect(out).toContain("</tab_response>");
+	});
+
+	it("notes that a running tab's response is its previous completed turn", async () => {
+		const tool = createReadTabTool(
+			makeCallbacks({
+				getLastResponse: () => ({ text: "older turn", status: "running" }),
+			}),
+		);
+		const out = await tool.execute({ tab_id: "targ" });
+		expect(out).toContain("still running");
+		expect(out).toContain("older turn");
+	});
+
+	it("explains when a tab has no completed response yet (idle)", async () => {
+		const tool = createReadTabTool(
+			makeCallbacks({
+				getLastResponse: () => ({ text: null, status: "idle" }),
+			}),
+		);
+		const out = await tool.execute({ tab_id: "targ" });
+		expect(out).toContain("no completed response");
+		expect(out).toContain("no assistant responses yet");
+	});
+
+	it("explains when a tab is still on its first turn (running, no prior text)", async () => {
+		const tool = createReadTabTool(
+			makeCallbacks({
+				getLastResponse: () => ({ text: null, status: "running" }),
+			}),
+		);
+		const out = await tool.execute({ tab_id: "targ" });
+		expect(out).toContain("no completed response");
+		expect(out).toContain("still working on its first turn");
+	});
+
+	it("rejects an empty tab_id and lists open handles", async () => {
+		const tool = createReadTabTool(makeCallbacks());
+		const out = await tool.execute({ tab_id: "" });
+		expect(out).toContain("Error");
+		expect(out).toContain("targ");
+	});
+
+	it("returns a helpful error when the id is unknown", async () => {
+		const tool = createReadTabTool(makeCallbacks({ resolveShortId: () => ({ status: "none" }) }));
+		const out = await tool.execute({ tab_id: "zzzz" });
+		expect(out).toContain("no open tab matches");
+		expect(out).toContain("Currently open tabs:");
+	});
+
+	it("asks for more characters when the id is ambiguous", async () => {
+		const tool = createReadTabTool(
+			makeCallbacks({
+				resolveShortId: () => ({
+					status: "ambiguous",
+					matches: [
+						{ id: "a1", title: "One", handle: "abcd1" },
+						{ id: "a2", title: "Two", handle: "abcd2" },
+					],
+				}),
+			}),
+		);
+		const out = await tool.execute({ tab_id: "abcd" });
+		expect(out).toContain("ambiguous");
+		expect(out).toContain("abcd1");
+		expect(out).toContain("abcd2");
+	});
+});
diff --git a/packages/core/tests/tools/send-to-tab.test.ts b/packages/core/tests/tools/send-to-tab.test.ts
new file mode 100644
index 0000000..4450fc5
--- /dev/null
+++ b/packages/core/tests/tools/send-to-tab.test.ts
@@ -0,0 +1,142 @@
+import { describe, expect, it, vi } from "vitest";
+import {
+	createSendToTabTool,
+	type SendToTabCallbacks,
+	type TabResolution,
+} from "../../src/tools/send-to-tab.js";
+
+function makeCallbacks(overrides: Partial<SendToTabCallbacks> = {}): SendToTabCallbacks {
+	return {
+		resolveShortId: (): TabResolution => ({
+			status: "ok",
+			tab: { id: "target-id", title: "Target", handle: "targ" },
+		}),
+		deliver: () => ({ status: "started" }),
+		listOpenHandles: () => [{ handle: "targ", title: "Target" }],
+		self: { id: "self-id", handle: "self" },
+		...overrides,
+	};
+}
+
+describe("createSendToTabTool — schema & description", () => {
+	it("exposes tab_id and message params and a fire-and-forget description", () => {
+		const tool = createSendToTabTool(makeCallbacks());
+		expect(tool.name).toBe("send_to_tab");
+		expect(tool.description).toContain("fire-and-forget");
+		expect(tool.description.toLowerCase()).toContain("queued");
+	});
+});
+
+describe("createSendToTabTool — execute()", () => {
+	it("delivers to a resolved target and reports the started status", async () => {
+		const deliver = vi.fn(() => ({ status: "started" as const }));
+		const tool = createSendToTabTool(makeCallbacks({ deliver }));
+		const out = await tool.execute({ tab_id: "targ", message: "hello there" });
+		expect(deliver).toHaveBeenCalledTimes(1);
+		const [targetId, delivered] = deliver.mock.calls[0] ?? [];
+		expect(targetId).toBe("target-id");
+		// Provenance prefix names the sending tab's handle.
+		expect(delivered).toContain("[message from tab self]");
+		expect(delivered).toContain("hello there");
+		expect(out).toContain("idle");
+		expect(out).toContain("targ");
+	});
+
+	it("reports the queued status when the target is busy", async () => {
+		const deliver = vi.fn(() => ({ status: "queued" as const }));
+		const tool = createSendToTabTool(makeCallbacks({ deliver }));
+		const out = await tool.execute({ tab_id: "targ", message: "ping" });
+		expect(out.toLowerCase()).toContain("queued");
+		expect(out.toLowerCase()).toContain("busy");
+	});
+
+	it("reports a HELD message when delivery is suppressed (auto-wake limit hit)", async () => {
+		const deliver = vi.fn(() => ({ status: "suppressed" as const }));
+		const tool = createSendToTabTool(makeCallbacks({ deliver }));
+		const out = await tool.execute({ tab_id: "targ", message: "ping again" });
+		expect(out).toContain("HELD");
+		expect(out.toLowerCase()).toContain("limit");
+		// It must steer the sender away from retrying in a loop.
+		expect(out.toLowerCase()).toContain("do not keep resending");
+		expect(out.toLowerCase()).toContain("human");
+	});
+
+	it("rejects an empty tab_id and lists open handles", async () => {
+		const tool = createSendToTabTool(makeCallbacks());
+		const out = await tool.execute({ tab_id: "  ", message: "hi" });
+		expect(out).toContain("Error");
+		expect(out).toContain("targ");
+	});
+
+	it("rejects an empty message", async () => {
+		const deliver = vi.fn(() => ({ status: "started" as const }));
+		const tool = createSendToTabTool(makeCallbacks({ deliver }));
+		const out = await tool.execute({ tab_id: "targ", message: "   " });
+		expect(out).toContain("Error");
+		expect(deliver).not.toHaveBeenCalled();
+	});
+
+	it("returns a helpful error and open-tab list when the id is unknown", async () => {
+		const deliver = vi.fn(() => ({ status: "started" as const }));
+		const tool = createSendToTabTool(
+			makeCallbacks({
+				resolveShortId: () => ({ status: "none" }),
+				deliver,
+			}),
+		);
+		const out = await tool.execute({ tab_id: "zzzz", message: "hi" });
+		expect(out).toContain("no open tab matches");
+		expect(out).toContain("Currently open tabs:");
+		expect(deliver).not.toHaveBeenCalled();
+	});
+
+	it("asks for more characters when the id is ambiguous", async () => {
+		const deliver = vi.fn(() => ({ status: "started" as const }));
+		const tool = createSendToTabTool(
+			makeCallbacks({
+				resolveShortId: () => ({
+					status: "ambiguous",
+					matches: [
+						{ id: "a1", title: "One", handle: "abcd1" },
+						{ id: "a2", title: "Two", handle: "abcd2" },
+					],
+				}),
+				deliver,
+			}),
+		);
+		const out = await tool.execute({ tab_id: "abcd", message: "hi" });
+		expect(out).toContain("ambiguous");
+		expect(out).toContain("abcd1");
+		expect(out).toContain("abcd2");
+		expect(deliver).not.toHaveBeenCalled();
+	});
+
+	it("refuses to send to its own tab", async () => {
+		const deliver = vi.fn(() => ({ status: "started" as const }));
+		const tool = createSendToTabTool(
+			makeCallbacks({
+				resolveShortId: () => ({
+					status: "ok",
+					tab: { id: "self-id", title: "Me", handle: "self" },
+				}),
+				deliver,
+			}),
+		);
+		const out = await tool.execute({ tab_id: "self", message: "hi" });
+		expect(out).toContain("cannot send a message to your own tab");
+		expect(deliver).not.toHaveBeenCalled();
+	});
+
+	it("surfaces a thrown delivery error instead of crashing", async () => {
+		const tool = createSendToTabTool(
+			makeCallbacks({
+				deliver: () => {
+					throw new Error("boom");
+				},
+			}),
+		);
+		const out = await tool.execute({ tab_id: "targ", message: "hi" });
+		expect(out).toContain("Error delivering message");
+		expect(out).toContain("boom");
+	});
+});
diff --git a/packages/core/tests/tools/summon.test.ts b/packages/core/tests/tools/summon.test.ts
index 6597c21..f59f345 100644
--- a/packages/core/tests/tools/summon.test.ts
+++ b/packages/core/tests/tools/summon.test.ts
@@ -39,9 +39,13 @@ describe("createSummonTool — description content", () => {
 				path: "/home/u/.config/dispatch/agents/researcher.toml",
 			},
 		];
-		const tool = createSummonTool("/tmp/work", noopCallbacks, agents, [], [
-			"/home/u/.config/dispatch/agents",
-		]);
+		const tool = createSummonTool(
+			"/tmp/work",
+			noopCallbacks,
+			agents,
+			[],
+			["/home/u/.config/dispatch/agents"],
+		);
 		expect(tool.description).toContain("programmer");
 		expect(tool.description).toContain("Programmer");
 		expect(tool.description).toContain("Implements code from a plan");