feat(native): add OpenCode terminal agent

[tlgimenes]

Summary

Stacked on #5557. Adds OpenCode as the third native-only xterm/PTY coding agent and hardens the shared native terminal experience for Claude Code, Codex, and OpenCode.

Dependency: review and merge #5557 first. This PR's review diff is feat/native-terminal-agents...feat/native-opencode-agent.

What changed

• Detect OpenCode 1.18.10+ and verify bounded runtime readiness before exposing it in the native picker.
• Launch a real OpenCode TUI with launch-scoped Studio instructions, lifecycle plugin, selected cms MCP, exact --session resume, provider-owned model selection, and provider-owned titles.
• Keep OpenCode terminal-only: it is not added to hosted/headless harness IDs, AI SDK dispatch, provider keys, or cloud model catalogs.
• Polish the native picker and startup flow with keyboard navigation, concise agent cards, a localized loading state, matching panel/terminal colors, and only xterm after launch—no Studio Ready/Interrupt toolbar.
• Start Codex in YOLO mode by default, disable its Desktop-app promotion, and pre-trust only Studio's exact managed hooks/workspace configuration.
• Avoid Claude/Codex folder-trust prompts without broadening trust to unrelated hooks or projects.
• Make resume/recovery restart-safe: preserve the last confirmed provider checkpoint, record exact missing-session rejection before fresh fallback, retain replay/capability-query authority across remounts, and prevent stale hooks from restoring rejected sessions or overwriting manual titles.
• Reap OpenCode processes and Codex preflight helpers across logout/account transitions and shutdown.

Hosted/native boundary

All CLI-agent renderer behavior is selected only by the native Tauri runtime. Hosted web continues to use structured Decopilot chat; it never exposes OpenCode or ships the terminal protocol in its production bundle.

Validation

Completed on the final rebased stack:

• bun run test — 5,689 passed, 0 failed across 617 files.
• Top native black-box contract — 109 passed, 0 failed, 889 assertions, covering all three providers, lifecycle, exact resume, missing-session recovery, process restart, and account fencing.
• Hosted runtime boundary E2E — 7 passed, 0 failed.
• cargo test --workspace and cargo clippy --workspace --all-targets -- -D warnings.
• bun run check, bun run lint, bun run knip, bun run fmt:check, and cargo fmt --all -- --check.
• Hosted and native production builds; the hosted bundle guard scanned 238 assets and found no desktop runtime.

Tauri DevTools acceptance exercised the final three-agent picker, keyboard wrapping, backgrounds, real Claude prompt/title/status/replay, and real Codex YOLO startup without trust/hook/Desktop notices. OpenCode's installed 1.18.10 binary was correctly marked try anyway because its existing pre-1.18 user database has an incomplete upstream migration; a fresh isolated 1.18.10 state enters the real TUI, while the product's fail-closed probe prevents a broken blank session.

Review feedback

All 23 existing review threads are resolved. The four hosted-selector findings became obsolete under the strict Decopilot-hosted / terminal-native split; the remaining findings have fixes and regression coverage in the final commits.

Migration notes

Native SQLite migrates from schema version 11 to 12 by adding rejected_provider_session_id. The migration clears legacy null-checkpoint barriers while preserving confirmed provider checkpoints. There is no hosted Postgres migration or hosted chat contract expansion.

Architecture and detailed validation evidence are in apps/native/docs/terminal-agents-plan.md.

[cubic-dev-ai]

All reported issues were addressed

<sub>Tip: cubic can generate docs of your entire codebase and keep them up to date. Try it here.

Re-trigger cubic</sub>

[cubic-dev-ai]

All reported issues were addressed across 50 files

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>

[cubic-dev-ai]

All reported issues were addressed across 9 files (changes from recent commits).

_{You’re at about 91% of the monthly reviewed-line limit. You may want to disable incremental reviews to conserve quota. Reviews will continue until that limit is exceeded. If you need help avoiding interruptions, please contact contact@cubic.dev.}

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>

[tlgimenes]

@cubic-dev-ai review this

[cubic-dev-ai]

@cubic-dev-ai review this

@tlgimenes I can't start this review because your workspace has reached its free monthly review limit. cubic has reviewed 42,059 of the 40,000 allowed lines of code this month. Reviews resume on 1 September 2026 (in 29 days). Paid plans include much higher monthly review limits. Upgrade now to resume reviews.

To help optimise your usage, you can tune cubic to get the most out of your usage limits:

• Stop reviewing test files
• Turn off incremental reviews
• Use the cubic CLI locally
• Skip non-default base branches

Learn more →

[tlgimenes]

Consolidation note: this PR was automatically marked merged when its exact validated head (3846114) was fast-forwarded into the base branch for #5557. No separate change landed on main; #5557 is now the sole open PR and contains the full three-agent implementation. This PR remains as review-history traceability.