Add pane state parser with test coverage

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/features/tmux-subagent/pane-state-querier.test.ts

@@ -0,0 +1,75 @@
+/// <reference types="bun-types/test" />
+
+import { describe, expect, it } from "bun:test"
+import { parsePaneStateOutput } from "./pane-state-parser"
+
+describe("parsePaneStateOutput", () => {
+  it("accepts a single pane when tmux omits the empty trailing title field", () => {
+    // given
+    const stdout = "%0\t120\t40\t0\t0\t1\t120\t40\n"
+
+    // when
+    const result = parsePaneStateOutput(stdout)
+
+    // then
+    expect(result).not.toBe(null)
+    expect(result).toEqual({
+      windowWidth: 120,
+      windowHeight: 40,
+      panes: [
+        {
+          paneId: "%0",
+          width: 120,
+          height: 40,
+          left: 0,
+          top: 0,
+          title: "",
+          isActive: true,
+        },
+      ],
+    })
+  })
+
+  it("handles CRLF line endings without dropping panes", () => {
+    // given
+    const stdout = "%0\t120\t40\t0\t0\t1\t120\t40\r\n%1\t60\t40\t60\t0\t0\t120\t40\tagent\r\n"
+
+    // when
+    const result = parsePaneStateOutput(stdout)
+
+    // then
+    expect(result).not.toBe(null)
+    expect(result?.panes).toEqual([
+      {
+        paneId: "%0",
+        width: 120,
+        height: 40,
+        left: 0,
+        top: 0,
+        title: "",
+        isActive: true,
+      },
+      {
+        paneId: "%1",
+        width: 60,
+        height: 40,
+        left: 60,
+        top: 0,
+        title: "agent",
+        isActive: false,
+      },
+    ])
+  })
+
+  it("preserves tabs inside pane titles", () => {
+    // given
+    const stdout = "%0\t120\t40\t0\t0\t1\t120\t40\ttitle\twith\ttabs\n"
+
+    // when
+    const result = parsePaneStateOutput(stdout)
+
+    // then
+    expect(result).not.toBe(null)
+    expect(result?.panes[0]?.title).toBe("title\twith\ttabs")
+  })
+})