New OMP chats default to ACP when the provider satisfies orca-native-chat-v1 #74

Summary

Make new OMP chats ACP structured sessions by default for users with the structured-chat preference. This happens only after every gating parity row passes, and only on hosts whose omp confirms orca-native-chat-v1. Existing legacy sessions and every unmigrated workflow stay explicitly routed to legacy.

Context

• 44madfire/orca#20: ACP becomes default only after the parity and reliability gates pass; legacy stays an explicit, capability-gated fallback.
• Invariant: "For every environment and workflow migrated from legacy OMP Chat to ACP, ACP must preserve or strengthen all existing user-visible and reliability guarantees. Workflows not yet at parity remain explicitly routed to the legacy implementation."
• Transport ownership: "v1 does not change transport ownership for an already-existing legacy OMP session. Existing sessions stay legacy; new supported sessions use ACP. Legacy→ACP adoption is a separate migration feature."
• Routing preference: prefersStructuredNativeChatByDefault (src/shared/structured-native-chat-launch-route.ts:77 @76d1b7b). Availability gate: Structured launch availability per registered agent, with legacy-chat fallback on decline #78. Opt-in and contract negotiation: Register omp acp as an opt-in structured ACP agent behind the availability gate #68. Contract definition: ACP contract orca-native-chat-v1: define, test, and advertise oh-my-pi#17.
• A new ACP chat has no PTY, so the legacy in-tab Terminal↔Chat toggle (src/renderer/src/components/native-chat/native-chat-availability.ts:42-60) is not migrated in v1 (D2).
• Mobile: stale builds show "Update to view" for registered-agent chats (src/main/runtime/rpc/methods/session-tab-agent-status-projection.ts:19,46 @76d1b7b) — D4.

Scope

• Default the OMP opt-in on (or remove it). Availability for the default requires orca-native-chat-v1 in agentCapabilities._meta["ohmypi.acp/contracts"] plus the standard capabilities. No other OMP marker is read.
• Existing legacy OMP tabs keep their transport.
• Toggle routing (D2): terminal-launched/detected OMP keeps the legacy toggle. ACP OMP chats show an explicit "Terminal view is not available for this chat" notice with an "Open OMP in a terminal tab" action.
• Re-run every gating row on macOS, Linux and Windows; record the results on Tracking: OMP Native Chat → ACP migration (v3 plan) #67.
• Diagnostics name why a host stays legacy. Add a changelog/docs entry.

Non-goals

• No legacy adoption (Post-cutover migration: adopt existing legacy OMP sessions into ACP chat #69), handoff (Post-cutover migration: persisted ACP↔Terminal handoff for OMP chats #84) or retirement (Legacy OMP chat retirement criteria, dead-code removal, upstream submission #77).
• No extension work (OMP ACP dialect: classify and bound the extension surface #75).

Depends on

• Resting model catalog for registered structured agents from their model probe spec #79
• OMP live timeline parity: messages, reasoning, tools, edits, errors, usage #70
• ACP compaction updates → compaction boundary and usage invalidation (provider-neutral) #80
• OMP commands, options and composer over ACP #71
• ACP elicitation forms and OMP approval-policy parity #81
• OMP dialect: mid-turn "Send now" steers via OMP's ACP steer extension #82
• Mobile: render and drive registered structured agents (provider-neutral) #72
• OMP ACP lifecycle: settlement, Stop, crash, restart, status, notifications #73
• Single-writer protection for ACP-held OMP sessions (resume guards, AI Vault ownership) #83
• ACP contract orca-native-chat-v1: define, test, and advertise oh-my-pi#17

Parity rows owned

• P-TOGL-01 (explicit routing of the in-tab toggle workflow). This unit also re-verifies every gating row as the default-on gate.

Acceptance criteria

• Every "Gates cutover" row on Tracking: OMP Native Chat → ACP migration (v3 plan) #67 is checked with a linked passing test.
• A host whose omp does not confirm orca-native-chat-v1 stays legacy with a named reason.
• Existing legacy OMP chats, WSL, runtime-owned SSH, Windows without start-time proof, terminal-launched and mobile-launched OMP all route exactly as before.
• Terminal OMP tabs keep the Terminal↔Chat toggle. ACP OMP chats show the explicit notice and action, never a silently missing toggle.
• Decisions D1–D14 are recorded on Tracking: OMP Native Chat → ACP migration (v3 plan) #67. The Mobile: render and drive registered structured agents (provider-neutral) #72 mobile build has shipped, or D4 says otherwise.

Required tests

• Contract gating: contract absent → legacy; present → ACP. Opt-in pre-contract behavior unchanged.
• Mixed-version paired host/client; upgrading with legacy OMP chats already open (they stay legacy).
• Real omp acp end-to-end smoke on macOS, Linux and Windows.

Base branch

acp-migration (44madfire/orca).