fix(tabs): only mention read_tab when the sender actually has it; CAPS on ONLY

The send_to_tab guidance previously told the agent it could call read_tab to
check for a reply, but the tab-messaging permissions are split — a tab can
hold send_to_tab WITHOUT read_tab (the exact case in testing). Advertising a
tool the agent wasn't granted is wrong.

Thread a canReadTab flag from AgentManager.buildTabCommToolEntries into
createSendToTabTool (true iff this tab is also granted read_tab). The tool
description and the delivery-result text now only reference read_tab when
canReadTab is true; otherwise they say a reply arrives on its own and to end
the turn. Drop the read_tab phrasing from the static TOOL_DESCRIPTIONS
one-liner (can't be conditional per-tab there).

Also uppercase ONLY in the recipient reply-contract footer for emphasis.

Tests: cover both canReadTab branches for description + result text; assert
ONLY is uppercased.

1 files changed, 32 insertions, 1 deletions

diff --git a/packages/core/tests/tools/send-to-tab.test.ts b/packages/core/tests/tools/send-to-tab.test.ts
index 68f8fa0..48ff460 100644
--- a/packages/core/tests/tools/send-to-tab.test.ts
+++ b/packages/core/tests/tools/send-to-tab.test.ts
@@ -14,6 +14,7 @@ function makeCallbacks(overrides: Partial<SendToTabCallbacks> = {}): SendToTabCa
 		deliver: () => ({ status: "started" }),
 		listOpenHandles: () => [{ handle: "targ", title: "Target" }],
 		self: { id: "self-id", handle: "self" },
+		canReadTab: true,
 		...overrides,
 	};
 }
@@ -28,6 +29,19 @@ describe("createSendToTabTool — schema & description", () => {
 		expect(tool.description.toLowerCase()).toContain("do not sleep");
 		expect(tool.description.toLowerCase()).toContain("end your turn");
 	});
+
+	it("mentions read_tab in the description only when canReadTab is true", () => {
+		const tool = createSendToTabTool(makeCallbacks({ canReadTab: true }));
+		expect(tool.description).toContain("read_tab");
+	});
+
+	it("never mentions read_tab in the description when canReadTab is false", () => {
+		const tool = createSendToTabTool(makeCallbacks({ canReadTab: false }));
+		expect(tool.description).not.toContain("read_tab");
+		// Still tells the agent a reply arrives on its own + to end its turn.
+		expect(tool.description.toLowerCase()).toContain("arrives on its own");
+		expect(tool.description.toLowerCase()).toContain("end your turn");
+	});
 });
 
 describe("createSendToTabTool — execute()", () => {
@@ -46,7 +60,7 @@ describe("createSendToTabTool — execute()", () => {
 		// Reply contract: the recipient must answer via send_to_tab back to the
 		// sender's handle, not as a plain text reply to its own user.
 		expect(delivered).toContain('send_to_tab tool with tab_id "self"');
-		expect(delivered.toLowerCase()).toContain("only reply if");
+		expect(delivered).toContain("ONLY reply if");
 		expect(out).toContain("idle");
 		expect(out).toContain("targ");
 		// Sender is steered away from busy-waiting and told to end its turn.
@@ -54,6 +68,23 @@ describe("createSendToTabTool — execute()", () => {
 		expect(out.toLowerCase()).toContain("end your turn");
 	});
 
+	it("points the sender at read_tab in the result only when canReadTab is true", async () => {
+		const deliver = vi.fn(() => ({ status: "started" as const }));
+		const tool = createSendToTabTool(makeCallbacks({ deliver, canReadTab: true }));
+		const out = await tool.execute({ tab_id: "targ", message: "hi" });
+		expect(out).toContain("read_tab");
+	});
+
+	it("omits read_tab from the result when canReadTab is false", async () => {
+		const deliver = vi.fn(() => ({ status: "started" as const }));
+		const tool = createSendToTabTool(makeCallbacks({ deliver, canReadTab: false }));
+		const out = await tool.execute({ tab_id: "targ", message: "hi" });
+		expect(out).not.toContain("read_tab");
+		// Still steers away from busy-waiting and toward ending the turn.
+		expect(out.toLowerCase()).toContain("do not sleep");
+		expect(out.toLowerCase()).toContain("end your turn");
+	});
+
 	it("reports the queued status when the target is busy", async () => {
 		const deliver = vi.fn(() => ({ status: "queued" as const }));
 		const tool = createSendToTabTool(makeCallbacks({ deliver }));