Add integration coverage for agent completion

[Kai Tao (vanzue)]

Summary

• add live TUI/conpty coverage for the /agent <prefix> completion introduced by Add agent subcommand autocomplete #487
• verify ghost-text rendering, Tab commitment, and Enter selection without rebuilding the current pane
• add release checklist coverage as C240 and C241
• repair the Add agent subcommand autocomplete #487 Rust completion fixtures for the AgentSource field added by Support profile-scoped WSL ACP agent backends #481

Integration boundary

The tests type and navigate through the packaged agent pane using wtcli send-keys, then assert the rendered TUI buffer, pane-session continuity, and persisted global setting.

Testing

• pwsh -NoProfile -File test/e2e/bootstrap.ps1 -Check
• pwsh -NoProfile -File test/e2e/Invoke-ItE2EReport.ps1 -Path test/e2e/tests/Feature.PerTabAgent.Tests.ps1 -UpdateReport (8 passed)
• cargo test --manifest-path tools/wta/Cargo.toml (1165 passed)
• full and incremental release reports mark C240 and C241 [x]

Target: #487

[Copilot]

Pull request overview

Adds end-to-end integration coverage for the /agent <prefix> completion behavior (introduced in #487) by driving the packaged agent pane via wtcli send-keys, and updates supporting fixtures/docs so the new release checklist items are tracked.

Changes:

• Adds two new Pester E2E cases validating /agent <prefix> completion rendering and keyboard acceptance (Tab commit, Enter selection) without pane rebuild.
• Fixes Rust slash-command test fixtures to populate the newly-required AvailableAgent.source field.
• Updates E2E documentation and the release checklist with new coverage items (C240/C241) and refreshed coverage counts.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
tools/wta/src/slash_command_tests.rs	Updates completion agent fixtures to include AgentSource::Host so Rust tests compile and reflect the new struct shape.
test/e2e/tests/Feature.PerTabAgent.Tests.ps1	Adds E2E coverage for /agent <prefix> completion (ghost text presence, Tab commitment, Enter selection safety).
test/e2e/README.md	Updates the E2E suite coverage table and coverage/test-count summaries to reflect the added cases.
doc/release-check-list.md	Adds new [E2E] checklist items C240/C241 for /agent prefix completion behavior and selection safety.