perf: reduce re-renders, fix mobile keyboard handling, add chunk load recovery, and improve PATH management (#1028)

* fix: exclude file content from reverted prompt text

Revert and fork now restore only the user's original prompt, not server-injected file content
Uses existing isSyntheticPart helper for type-safe filtering

* fix: keep scrollbar visible when hovering over thumb

* fix: prevent ESC abort from triggering when terminal is focused

* fix: pass directory to permission/question reply calls so approvals actually resolve

* fix: default model selection not responding after Base UI migration

* fix: prevent modal content from shifting and clipping footer buttons

* fix: improve session switching performance and add sub-agent export with prompt collapse

Defer viewport anchor saving to eliminate ~800ms UI freeze when switching sessions
Add export dialog to include sub-agent tasks recursively in markdown export
Add collapse chevron button for expanded user prompts in sticky header

* fix: resolve sidebar scroll and TDZ crash in session sidebar

* perf: reduce CPU overhead and re-renders across chat, layout, and settings

* fix: position collapse button at top of message and prevent ESC abort in terminal

* fix: position collapse button at top and add padding only when expanded

* refactor: extract shared PATH utilities and mobile keyboard hook

* refactor: import shared path-utils in electron, use module-level style constants

- Electron now imports pathLooksUserConfigured/mergePathValues from
  shared path-utils.js instead of inline duplication
- ToolPart collapsedCustomStyle moved from useMemo([]) to module const

* fix: resolve remaining merge conflicts and type errors

- Remove duplicate variable declarations in SessionNodeItem
- Remove orphaned export callback body from conflict resolution
- Fix HelpDialog description -> descriptionKey (i18n rename)

* fix: resolve type-check and lint errors in session-actions.test.ts

- Added missing bun:test type declarations (beforeEach, mock, mock.module)
- Removed unused State import
- Replaced 'as any' casts with proper OpencodeClient and ChildStoreManager types
- Added eslint-disable for unused _ parameter in mock function

* fix PR 1028 export and PATH edge cases

* fix startup retry exhaustion state

* remove opencode package lock change

* fix sub-session rename cancellation

---------

Co-authored-by: Bohdan Triapitsyn <artmore@protonmail.com>

packages/ui/src/lib/messages/synthetic.test.ts

@@ -0,0 +1,123 @@
+import { describe, expect, test } from "bun:test"
+import type { Part } from "@opencode-ai/sdk/v2"
+import { isSyntheticPart, isFullySyntheticMessage, filterSyntheticParts } from "./synthetic"
+
+function createTextPart(id: string, text: string, synthetic?: boolean): Part {
+  return {
+    id,
+    sessionID: "session-1",
+    messageID: "message-1",
+    type: "text",
+    text,
+    ...(synthetic !== undefined ? { synthetic } : {}),
+  } as Part
+}
+
+function createFilePart(id: string, url: string): Part {
+  return {
+    id,
+    sessionID: "session-1",
+    messageID: "message-1",
+    type: "file",
+    mime: "text/plain",
+    url,
+  } as Part
+}
+
+describe("isSyntheticPart", () => {
+  test("returns false for undefined", () => {
+    expect(isSyntheticPart(undefined)).toBe(false)
+  })
+
+  test("returns false for non-object", () => {
+    expect(isSyntheticPart(null as unknown as Part)).toBe(false)
+    expect(isSyntheticPart("string" as unknown as Part)).toBe(false)
+  })
+
+  test("returns false for parts without synthetic property", () => {
+    const part = createTextPart("1", "hello")
+    expect(isSyntheticPart(part)).toBe(false)
+  })
+
+  test("returns false for parts with synthetic: false", () => {
+    const part = createTextPart("1", "hello", false)
+    expect(isSyntheticPart(part)).toBe(false)
+  })
+
+  test("returns true for parts with synthetic: true", () => {
+    const part = createTextPart("1", "file content here", true)
+    expect(isSyntheticPart(part)).toBe(true)
+  })
+
+  test("returns false for file parts", () => {
+    const part = createFilePart("1", "file:///path/to/file")
+    expect(isSyntheticPart(part)).toBe(false)
+  })
+})
+
+describe("isFullySyntheticMessage", () => {
+  test("returns false for undefined", () => {
+    expect(isFullySyntheticMessage(undefined)).toBe(false)
+  })
+
+  test("returns false for empty array", () => {
+    expect(isFullySyntheticMessage([])).toBe(false)
+  })
+
+  test("returns false when all parts are non-synthetic", () => {
+    const parts = [
+      createTextPart("1", "hello"),
+      createFilePart("2", "file:///path"),
+    ]
+    expect(isFullySyntheticMessage(parts)).toBe(false)
+  })
+
+  test("returns false when some parts are synthetic", () => {
+    const parts = [
+      createTextPart("1", "user prompt"),
+      createTextPart("2", "file content", true),
+    ]
+    expect(isFullySyntheticMessage(parts)).toBe(false)
+  })
+
+  test("returns true when all parts are synthetic", () => {
+    const parts = [
+      createTextPart("1", "file content 1", true),
+      createTextPart("2", "file content 2", true),
+    ]
+    expect(isFullySyntheticMessage(parts)).toBe(true)
+  })
+})
+
+describe("filterSyntheticParts", () => {
+  test("returns empty array for undefined", () => {
+    expect(filterSyntheticParts(undefined)).toEqual([])
+  })
+
+  test("returns empty array for empty array", () => {
+    expect(filterSyntheticParts([])).toEqual([])
+  })
+
+  test("returns all parts when no synthetic parts exist", () => {
+    const parts = [
+      createTextPart("1", "hello"),
+      createFilePart("2", "file:///path"),
+    ]
+    expect(filterSyntheticParts(parts)).toEqual(parts)
+  })
+
+  test("filters out synthetic parts when non-synthetic parts exist", () => {
+    const userPart = createTextPart("1", "user prompt")
+    const syntheticPart = createTextPart("2", "file content", true)
+    const parts = [userPart, syntheticPart]
+    expect(filterSyntheticParts(parts)).toEqual([userPart])
+  })
+
+  test("keeps synthetic parts when all parts are synthetic", () => {
+    const parts = [
+      createTextPart("1", "file content 1", true),
+      createTextPart("2", "file content 2", true),
+    ]
+    expect(filterSyntheticParts(parts)).toEqual(parts)
+  })
+})