feat: add experimental OpenCode v2 support

[oribarilan]

Summary

Refs #80.

Add experimental OpenCode v2 support without dropping v1 or duplicating the Vim engine.

• Export both v1 tui(api, options) and v2 setup(context) through the existing ./tui entry. The v2 adapter handles input, commands, storage, forms, permissions and cleanup; the pure Vim engine is unchanged.
• Keep the renderer-based input hook because public v2 layers cannot capture arbitrary normal-mode or replacement characters. Custom v2 leaders use an explicit experimentalV2Leader option.
• Normalize visual h/l selection while preserving the native anchor for subsequent word, line and vertical motions, including empty buffers and EOF/EOL boundaries. Re-anchor visual mode when the focused editor changes.
• Add just dev2 for local development on pinned OpenCode 2.0.15, with isolated .dev2/ settings/history and an optional binary override. just dev remains the v1 route.
• Add an optional exact-state, installed-package compatibility harness and version-specific installation/options documentation.
• Address review findings: reject JSON/JSONC project-config ancestors before packaging or launching the harness, test direct and symlinked output paths for both hosts, and forward host-owned selection colors without importing @opentui/core types.

The package remains ./tui-only. No root-export workaround or new package dependency is added. The initial v1 cold-install failure was isolated to a symlink-spelled XDG cache; canonical-cache Git and tarball installations worked.

Validation

Runtime validation was performed at d8050f765b6c2c4e7fdc700d8345c1c5752644cb, whose GitHub CI passed. The 7d791d2 follow-up changes only documentation; local lint and both unit suites passed again. Installed sources and the package manifest are unchanged.

• just check: lint clean, 337 Bun tests passed.
• just compat-unit: 16 Python tests passed, including 24 ancestor-config scenarios (six filenames × two host modes × direct/symlinked paths), fresh-observer checks and durable cleanup-failure receipts.
• git diff --check: passed.
• Real-host checks on macOS ARM64 tested both tarball and pinned Git installations, with isolated state and byte-for-byte verification of installed source files and the manifest:

Host	Install source	Cold install	Warm install	Exact-state checks passed	Named known gaps
OpenCode 1.18.33	Tarball	Passed	Passed	39	2
OpenCode 1.18.33	Git at d8050f7	Passed	Passed	39	2
OpenCode 2.0.15	Tarball	Passed	Passed	48	2
OpenCode 2.0.15	Git at d8050f7	Passed	Passed	48	2

The Git runs used vimcode@git+https://github.com/oribarilan/vimcode.git#d8050f765b6c2c4e7fdc700d8345c1c5752644cb. A temporary configure wrapper reused the existing harness, replacing only its install spec. The tarball in each Git receipt was a source/manifest reference, not the installed package.

The host checks cover physical and seeded visual selection, mixed motions, empty-buffer and EOF/EOL handling, Unicode replacement/consumption, custom leader, autocomplete and palette behavior. v2 checks also cover a real editor switch, root/child forms, permission rejection, disable and unload/reload. Tests use synthetic text, with no model requests or permission approvals.

The maintainer also reported successful manual smoke tests through both just dev and just dev2.

Remaining limits

This is experimental compatibility, not a full-parity or all-versions support declaration.

• v2 input still depends on raw renderer listener ordering and explicit leader mirroring.
• Inherited tab/wide/combining-character offset issues and snapshot-based redo remain. The harness reports tab-inner-word-offset and snapshot-redo as known gaps, not passes.
• Native nonhorizontal selection endpoint differences are preserved rather than hidden.
• OpenCode v2.0.20 and non-macOS runtime behavior have not been validated.
• A clean-dependency bun run typecheck reports the same eight pre-existing baseline errors; the new unresolved @opentui/core diagnostic was removed.

See docs/opencode-v2-poc.md for launch/test commands and docs/opencode-v2-strategy.md for the evidence and trade-offs. No upstream reports have been posted. This PR does not create a release; the released v0.18.1 tag remains v1-only.

[seth-heinz]

@oribarilan Any idea when you plan to get this merged?

[oribarilan]

@seth-heinz Will be released in in next few days :) just doing some more QA

[oribarilan]

@seth-heinz v0.19.0 is out :) Release notes

v2 support is still experimental. The README has separate install instructions for v1 and v2. thanks for waiting!