Add OpenCode ACP agent support

[vanzue]

Summary

• add OpenCode as a built-in ACP and delegate agent
• launch agent panes with opencode acp and interactive delegation tabs with opencode --prompt <prompt>
• support protocol-based model selection, setup guidance, policy filtering, and telemetry
• add the official OpenCode mark to the agent pane header

Validation

• cargo test --target x86_64-pc-windows-msvc --manifest-path tools/wta/Cargo.toml (1115 passed)
• cargo build --target x86_64-pc-windows-msvc --manifest-path tools/wta/Cargo.toml
• cmd.exe /c "tools\razzle.cmd && bcz no_clean"
• TerminalApp and CascadiaPackage bx builds
• local MSIX deployment and OpenCode 1.17.18 launch
• live ?<prompt> delegation verified to launch the interactive OpenCode TUI and keep the tab open
• session
• agent pane, auto fix works as expected

Limitations

• OpenCode shell-session hooks and history discovery are not included

Fixes #460

[Copilot]

Pull request overview

Adds OpenCode as a first-class agent option across the WTA (Rust) and Terminal (C++/XAML) surfaces, wiring up ACP hosting (opencode acp), delegate execution (opencode run), and the corresponding UI/telemetry/docs touchpoints.

Changes:

• Extend the WTA agent registry and coordinator tests to recognize/launch OpenCode in ACP and delegate modes.
• Update Terminal settings plumbing (agent command expansion + telemetry sanitization) to treat opencode as a built-in agent ID.
• Add OpenCode branding (agent pane header mark + packaged SVG) and update README/FAQ to include OpenCode.

Reviewed changes

Copilot reviewed 12 out of 13 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
tools/wta/src/main.rs	Updates CLI documentation to include opencode and generalizes ACP model flag wording.
tools/wta/src/coordinator.rs	Adds tests asserting delegate invocation uses opencode run in WSL + PowerShell base64 flows.
tools/wta/src/agent_registry.rs	Adds OpenCode as a known agent and introduces acp_model_flags to represent protocol-only ACP model selection.
tools/wta/src/agent_check.rs	Treats OpenCode like Gemini for login subcommand selection (auth login).
src/cascadia/TerminalSettingsModel/CascadiaSettingsSerialization.cpp	Allows opencode through telemetry sanitization as a built-in provider id.
src/cascadia/TerminalSettingsEditor/AIAgentsViewModel.cpp	Expands "opencode" into the concrete ACP launch command (opencode acp).
src/cascadia/TerminalApp/TerminalPage.cpp	Expands "opencode" into the concrete ACP launch command (opencode acp) when launching panes.
src/cascadia/TerminalApp/AgentPaneContent.xaml	Adds OpenCode mark vector to the agent pane header logo cluster.
src/cascadia/TerminalApp/AgentPaneContent.cpp	Adds OpenCode logo selection and visibility toggling in code-behind.
src/cascadia/inc/AgentRegistry.h	Adds OpenCode to built-in ACP + delegate agent lists.
src/cascadia/CascadiaPackage/AgentIcons/opencode.svg	Adds the packaged OpenCode SVG asset.
README.md	Documents OpenCode as an auto-detected ACP-capable agent in the quickstart.
doc/faq.md	Updates custom-agent FAQ to mention OpenCode and clarifies session-tracking-hook limitation.

[Copilot]

Pull request overview

Copilot reviewed 12 out of 13 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 12 out of 13 changed files in this pull request and generated 4 comments.

[Copilot]

Pull request overview

Copilot reviewed 12 out of 13 changed files in this pull request and generated no new comments.

[Copilot]

Pull request overview

Copilot reviewed 13 out of 14 changed files in this pull request and generated no new comments.

[Copilot]

Pull request overview

Copilot reviewed 13 out of 14 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 13 out of 14 changed files in this pull request and generated no new comments.