#19045 test(cmux-next): add folder trust gallery coverage

Summary

Add gallery coverage for the folder trust line above the composer. The entry captures the ask, Trust and Don't trust decisions, Undo, failed save, remote-only messaging, and the already-decided states. Removing the allowlist row makes coverage enforce the entry.

Validation

• bun run --cwd webviews typecheck
• bun test test/gallery-coverage.test.ts
• bun test test/gallery-env.test.ts test/pane-english.test.ts
• bun run gallery:build
• bun run --cwd webviews fmt -- --check
• git diff --check

Changelog

• Added: Gallery states and decision interactions for folder trust prompts.

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Summary by cubic

Adds gallery coverage for the folder trust ask above the composer, replacing the allowlist exemption for TrustAsk.tsx.

The fixture covers Trust and Don't trust decisions, Undo, failed save, remote-only messaging, and already-decided states.

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[!NOTE]
Low Risk
Gallery and test-infra only; fixtures are not shipped UI and do not change runtime trust behavior.

Overview
Adds a gallery entry for the agent pane folder trust prompt (TrustAsk), so visual/regression coverage is enforced instead of allowlisted.

The new TrustAsk.gallery.tsx wires TrustAsk in a composer shell with variants for the initial ask, failed and remote states, and already decided trusted/untrusted outcomes. Play scripts exercise Trust, Don't trust, and Undo and assert the expected trust-line copy and buttons.

Removes TrustAsk from gallery-coverage.allowlist.json, so the coverage test requires this entry via covers: ["agent-session/acpmux/TrustAsk.tsx#TrustAsk"].

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