feat(skill_mcp): add dynamic truncation and grep filtering

- Add skill_mcp and webfetch to TRUNCATABLE_TOOLS list
- Add grep parameter for regex filtering of output lines
- Prevents token overflow from large MCP responses

🤖 GENERATED WITH ASSISTANCE OF [OhMyOpenCode](https://github.com/code-yeongyu/oh-my-opencode)

src/tools/skill-mcp/tools.test.ts

@@ -1,5 +1,5 @@
 import { describe, it, expect, beforeEach, mock } from "bun:test"
-import { createSkillMcpTool } from "./tools"
+import { createSkillMcpTool, applyGrepFilter } from "./tools"
 import { SkillMcpManager } from "../../features/skill-mcp-manager"
 import type { LoadedSkill } from "../../features/opencode-skill-loader/types"
 
@@ -147,5 +147,69 @@ describe("skill_mcp tool", () => {
       expect(tool.description.length).toBeLessThan(200)
       expect(tool.description).toContain("mcp_name")
     })
+
+    it("includes grep parameter in schema", () => {
+      // #given / #when
+      const tool = createSkillMcpTool({
+        manager,
+        getLoadedSkills: () => [],
+        getSessionID: () => "session",
+      })
+
+      // #then
+      expect(tool.description).toBeDefined()
+    })
+  })
+})
+
+describe("applyGrepFilter", () => {
+  it("filters lines matching pattern", () => {
+    // #given
+    const output = `line1: hello world
+line2: foo bar
+line3: hello again
+line4: baz qux`
+
+    // #when
+    const result = applyGrepFilter(output, "hello")
+
+    // #then
+    expect(result).toContain("line1: hello world")
+    expect(result).toContain("line3: hello again")
+    expect(result).not.toContain("foo bar")
+    expect(result).not.toContain("baz qux")
+  })
+
+  it("returns original output when pattern is undefined", () => {
+    // #given
+    const output = "some output"
+
+    // #when
+    const result = applyGrepFilter(output, undefined)
+
+    // #then
+    expect(result).toBe(output)
+  })
+
+  it("returns message when no lines match", () => {
+    // #given
+    const output = "line1\nline2\nline3"
+
+    // #when
+    const result = applyGrepFilter(output, "xyz")
+
+    // #then
+    expect(result).toContain("[grep] No lines matched pattern")
+  })
+
+  it("handles invalid regex gracefully", () => {
+    // #given
+    const output = "some output"
+
+    // #when
+    const result = applyGrepFilter(output, "[invalid")
+
+    // #then
+    expect(result).toBe(output)
   })
 })