chore: retire v1 SpecGit acceptance gate

[LeXwDeX]

Why

The dedicated SpecGit Acceptance workflow is a v1.11.0 gate that depends on retired v1 policy and no longer matches this repository's supported PR validation. Retire that gate while keeping the independent project checks in place.

Changes

• Delete .github/workflows/specgit-accept.yml.
• Update AGENTS.md to refer to the existing .github/workflows/pr-checks.yml workflow.
• Preserve pr-checks.yml, publish.yml, all project validation jobs, and branch protection unchanged.

This retires the dedicated v1 acceptance gate only. It does not claim that all v1 assets have been removed or that the repository's full v1-to-v2 migration is complete.

Validation

Local checks ran on Darwin 27.0.0 arm64 with Node 26.8.1 and npm 12.0.2. The GitHub Actions workflow uses Ubuntu, so current-head Linux CI remains necessary.

SG-MIG-05A — project checks

• npm ci --no-audit --no-fund — exit 0.
• npm run format:check — exit 0.
• npm run typecheck — exit 0.
• npm test — 104/104 passed.
• npm run check:package — exit 0; package verification passed with 33 tarball entries.
• The configured private registry returned HTTP 403 for npm audit; rerunning npm audit --audit-level=high --registry=https://registry.npmjs.org returned exit 0 and 0 vulnerabilities.

SG-MIG-05B — pinned host integration

• npm run test:host built the plugin and passed 17/17 host contract tests against OpenCode-GraphAgent commit 8d9972908c308da1836a004cebe27c7c23db1acc.
• Host dependencies were installed with Bun 1.4.0 using bun install --frozen-lockfile --ignore-scripts --filter './packages/opencode'.

SG-MIG-05C — compatibility matrix

Each target used an independent source and dependency directory. For both targets, npm ci --no-audit --no-fund, the CI target-package install, npm run typecheck, npm run build, and node -e "import('./dist/index.js')" all exited 0. The package lockfile was unchanged.

CI target	Resolved @opencode-ai/plugin / @opencode-ai/sdk
1.4.3	1.4.3 / 1.4.3
latest (resolved 2026-09-26 04:12 UTC)	1.18.32 / 1.18.32

Closes #66