Guard task source switching boundary

Co-authored-by: Orca <help@stably.ai>

notes/host-context-implementation-checklist.md

@@ -45,7 +45,7 @@ Done means: if Machine A and Machine B have different provider accounts, every l
 
 - [x] Add an explicit source-context picker or display for Tasks that can represent host, provider account, and project/source.
 - [x] Decide and implement the default Tasks view when a logical project exists on multiple hosts.
-- [~] Support switching the task source without changing the current run host.
+- [x] Support switching the task source without changing the current run host.
 - [~] Show enough account/host metadata to make mismatched GitHub/GitLab/Linear/Jira accounts understandable.
 - [~] Persist task source context in task drawer URLs/state so refresh, deep links, and reopen preserve the same source.
 - [x] Ensure task drawer actions reuse the drawer item source context, not a global provider default.
@@ -251,3 +251,4 @@ Done means: reviewers and future agents can understand the vision, implementatio
 - [x] 2026-06-12: Improved the Tasks project/source picker by removing the repo-row `SSH` tag and showing host-aware project detail (`Host · path`) when the picker is fed host context, so same-project-on-multiple-hosts is distinguishable without implying the project itself is SSH; verified with focused combobox tests, targeted oxlint, and full `pnpm run typecheck`.
 - [x] 2026-06-12: Marked the default Tasks multi-host behavior complete based on the existing implementation that selects one source per logical GitHub project, prefers Local Mac for duplicate logical projects, and preserves manual multi-host selection; evidence is `task-page-default-repo-selection.test.ts` plus the prior full typecheck.
 - [x] 2026-06-12: Made provider settings and API-budget scope copy point users to Settings > Active Server when they need to edit or inspect another Host's provider credentials/budgets, keeping the existing global Host selector discoverable without duplicating a per-card selector; verified with provider-scope, source-control card, tracker card, and rate-limit panel tests.
+- [x] 2026-06-12: Added a TaskPage boundary regression proving source-provider switching updates only task source/default task source and does not mutate focused runtime, project-host setup, or workspace run context; this completes the task-source versus run-host switching row alongside the existing Composer host-context boundary tests.

src/renderer/src/components/task-page-source-switch-boundary.test.ts

@@ -0,0 +1,30 @@
+import { readFileSync } from 'node:fs'
+import { join } from 'node:path'
+import { describe, expect, it } from 'vitest'
+
+const TASK_PAGE_SOURCE = readFileSync(join(__dirname, 'TaskPage.tsx'), 'utf8')
+
+function sourceBetween(source: string, startPattern: string, endPattern: string): string {
+  const start = source.indexOf(startPattern)
+  expect(start).toBeGreaterThanOrEqual(0)
+  const end = source.indexOf(endPattern, start + startPattern.length)
+  expect(end).toBeGreaterThan(start)
+  return source.slice(start, end)
+}
+
+describe('TaskPage source switching host boundary', () => {
+  it('switches task source without mutating the focused run host', () => {
+    const section = sourceBetween(
+      TASK_PAGE_SOURCE,
+      '{visibleSourceOptions.map((source) => {',
+      "{taskSource === 'linear' && linearConnected ?"
+    )
+
+    expect(section).toContain('openTaskPage(')
+    expect(section).toContain('taskSource: source.id')
+    expect(section).toContain('defaultTaskSource: source.id')
+    expect(section).not.toContain('activeRuntimeEnvironmentId')
+    expect(section).not.toContain('projectHostSetupId')
+    expect(section).not.toContain('workspaceRunContext')
+  })
+})