fix(keyword-detector): use mainSessionID for session check instead of unreliable API

The keyword-detector was using ctx.client.session.get() to check parentID for
determining subagent sessions, but this API didn't reliably return parentID.

This caused non-ultrawork keywords (search, analyze) to be injected in subagent
sessions when they should only work in main sessions.

Changed to use getMainSessionID() comparison, consistent with other hooks like
session-notification and todo-continuation-enforcer.

- Replace unreliable parentID API check with mainSessionID comparison
- Add comprehensive test coverage for session filtering behavior
- Remove unnecessary session.get API call

src/hooks/keyword-detector/index.test.ts

@@ -0,0 +1,125 @@
+import { describe, expect, test, beforeEach, afterEach, spyOn } from "bun:test"
+import { createKeywordDetectorHook } from "./index"
+import { setMainSession } from "../../features/claude-code-session-state"
+import * as sharedModule from "../../shared"
+
+describe("keyword-detector session filtering", () => {
+  let logCalls: Array<{ msg: string; data?: unknown }>
+
+  beforeEach(() => {
+    setMainSession(undefined)
+    logCalls = []
+    spyOn(sharedModule, "log").mockImplementation((msg: string, data?: unknown) => {
+      logCalls.push({ msg, data })
+    })
+  })
+
+  afterEach(() => {
+    setMainSession(undefined)
+  })
+
+  function createMockPluginInput(options: { toastCalls?: string[] } = {}) {
+    const toastCalls = options.toastCalls ?? []
+    return {
+      client: {
+        tui: {
+          showToast: async (opts: any) => {
+            toastCalls.push(opts.body.title)
+          },
+        },
+      },
+    } as any
+  }
+
+  test("should skip non-ultrawork keywords in non-main session (using mainSessionID check)", async () => {
+    // #given - main session is set, different session submits search keyword
+    const mainSessionID = "main-123"
+    const subagentSessionID = "subagent-456"
+    setMainSession(mainSessionID)
+
+    const hook = createKeywordDetectorHook(createMockPluginInput())
+    const output = {
+      message: {} as Record<string, unknown>,
+      parts: [{ type: "text", text: "search mode 찾아줘" }],
+    }
+
+    // #when - non-main session triggers keyword detection
+    await hook["chat.message"](
+      { sessionID: subagentSessionID },
+      output
+    )
+
+    // #then - search keyword should be filtered out based on mainSessionID comparison
+    const skipLog = logCalls.find(c => c.msg.includes("Skipping non-ultrawork keywords in non-main session"))
+    expect(skipLog).toBeDefined()
+  })
+
+  test("should allow ultrawork keywords in non-main session", async () => {
+    // #given - main session is set, different session submits ultrawork keyword
+    const mainSessionID = "main-123"
+    const subagentSessionID = "subagent-456"
+    setMainSession(mainSessionID)
+
+    const toastCalls: string[] = []
+    const hook = createKeywordDetectorHook(createMockPluginInput({ toastCalls }))
+    const output = {
+      message: {} as Record<string, unknown>,
+      parts: [{ type: "text", text: "ultrawork mode" }],
+    }
+
+    // #when - non-main session triggers ultrawork keyword
+    await hook["chat.message"](
+      { sessionID: subagentSessionID },
+      output
+    )
+
+    // #then - ultrawork should still work (variant set to max)
+    expect(output.message.variant).toBe("max")
+    expect(toastCalls).toContain("Ultrawork Mode Activated")
+  })
+
+  test("should allow all keywords in main session", async () => {
+    // #given - main session submits search keyword
+    const mainSessionID = "main-123"
+    setMainSession(mainSessionID)
+
+    const hook = createKeywordDetectorHook(createMockPluginInput())
+    const output = {
+      message: {} as Record<string, unknown>,
+      parts: [{ type: "text", text: "search mode 찾아줘" }],
+    }
+
+    // #when - main session triggers keyword detection
+    await hook["chat.message"](
+      { sessionID: mainSessionID },
+      output
+    )
+
+    // #then - search keyword should be detected (output unchanged but detection happens)
+    // Note: search keywords don't set variant, they inject messages via context-injector
+    // This test verifies the detection logic runs without filtering
+    expect(output.message.variant).toBeUndefined() // search doesn't set variant
+  })
+
+  test("should allow all keywords when mainSessionID is not set", async () => {
+    // #given - no main session set (early startup or standalone mode)
+    setMainSession(undefined)
+
+    const toastCalls: string[] = []
+    const hook = createKeywordDetectorHook(createMockPluginInput({ toastCalls }))
+    const output = {
+      message: {} as Record<string, unknown>,
+      parts: [{ type: "text", text: "ultrawork search" }],
+    }
+
+    // #when - any session triggers keyword detection
+    await hook["chat.message"](
+      { sessionID: "any-session" },
+      output
+    )
+
+    // #then - all keywords should work
+    expect(output.message.variant).toBe("max")
+    expect(toastCalls).toContain("Ultrawork Mode Activated")
+  })
+})