Mobile: support OpenCode in native Chat UI #9308

Summary

Add OpenCode support to the mobile native Chat UI so OpenCode sessions can be viewed on iOS/Android companion the same way Claude / Codex (and other chat-capable agents) are today.

Context

Mobile native chat eligibility goes through the shared support set:

// src/shared/native-chat-agent-support.ts
NATIVE_CHAT_SUPPORTED_AGENTS = claude | openclaude | codex | grok

Mobile resolves chat via resolveMobileNativeChat / canShowMobileNativeChat (mobile/src/session/mobile-native-chat-eligibility.ts), which calls isNativeChatSupportedAgent. OpenCode is recognized as an agent for TUI launch/status on mobile, but not for native chat.

Desktop tracks OpenCode chat separately; mobile needs its own UI, transport, and session-preference work.

Expected

On mobile:

1. Long-press / view preference can open an OpenCode session in native Chat UI when the host can read the transcript.
2. History loads; live append works over the mobile runtime/RPC path.
3. Messages render readably on small screens (user / assistant / tools as supported).
4. Send / interrupt (if offered for other agents on mobile) work for OpenCode within the same product rules.
5. If transcript is not host-readable (e.g. certain remote layouts), gate cleanly like Grok’s local-readability check—no crash, optional terminal-only fallback.

Actual

isNativeChatSupportedAgent('opencode') is false → mobile chat toggle / resolution returns null for OpenCode tabs.

Implementation notes (mobile)

Likely touch points:

• Shared: src/shared/native-chat-agent-support.ts (coordinate with desktop; shared gate)
• Host/runtime: OpenCode transcript read + subscribe (same main/native-chat or relay path desktop uses)
• mobile/src/session/mobile-native-chat-eligibility.ts — eligibility once support is true
• Mobile chat merge / stream / empty states
• Session view preferences (terminal vs chat) for OpenCode tabs
• Tests under mobile/src/session/ for eligibility and merge

Depends on knowing OpenCode transcript path + schema on the host Orca is connected to.

Acceptance

• OpenCode session tab can enter native chat on mobile when transcript is readable
• History + live updates work over the companion connection
• Preference terminal ↔ chat works for OpenCode
• Remote/unreadability cases degrade safely
• No regression for existing mobile chat agents

Related

• Desktop counterpart: Desktop: support OpenCode in native Chat UI #9307
• Shared gate: src/shared/native-chat-agent-support.ts
• Mobile eligibility: mobile/src/session/mobile-native-chat-eligibility.ts