Fix /restart after ACP initialization failure

[Kai Tao (vanzue)]

Summary

• keep /restart event forwarding alive independently of the ACP connection task
• allow failed and degraded helpers to request restart_agent_stack after ACP initialization exits
• cover restart forwarding without an active ACP connection

Root cause

When ACP initialization failed, run_acp_client_over_pipe returned and dropped restart_rx. The UI still changed to Connecting("Restarting agent..."), but its restart send targeted the closed channel and the error was ignored, leaving the pane stuck indefinitely.

Validation

• cargo test --manifest-path tools\wta\Cargo.toml (1321 passed)
• explicit-target Debug WTA build
• hot-refreshed the loose Debug package
• restarted from a degraded helper and confirmed OpenCode 1.18.7 initialized in 2.27s and session/new succeeded

[Copilot]

Pull request overview

This PR fixes a recovery dead-end in the WTA helper when ACP initialization fails by keeping /restart forwarding alive independently of the ACP client task, allowing Windows Terminal to force-restart the entire agent stack even after the ACP task has exited.

Changes:

• Moved /restart event forwarding out of run_acp_client_over_pipe into a dedicated forwarder task that survives ACP initialization failure.
• Updated helper/app wiring to spawn the restart forwarder outside the ACP connection lifecycle.
• Added a unit test ensuring restart forwarding works without an active ACP connection.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
tools/wta/src/protocol/acp/client.rs	Introduces the standalone restart forwarder + adds a test; removes /restart handling from the ACP select loop.
tools/wta/src/helper/runtime.rs	Spawns the restart forwarder alongside channel creation so it survives master/ACP failures.
tools/wta/src/app.rs	Removes deferred restart receiver plumbing and spawns the restart forwarder when rebuilding ACP channels post-failure.
tools/wta/src/app_events.rs	Drops the now-removed restart_rx field from deferred ACP parameter initialization.

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

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

Suppressed comments (1)

tools/wta/src/helper/runtime.rs:461

• The comment says the ACP client forwards /restart to C++, but restart forwarding is now handled by the independent forwarder (outside the ACP task). Updating this comment will avoid confusion about which component is responsible for publishing restart_agent_stack.

            // /restart channel: App emits a RestartRequest, the ACP client
            // forwards to C++ independently of the ACP connection. Keeping
            // this receiver outside the ACP task preserves recovery after a
            // handshake failure.