feat: add V1/V2 compatibility foundation and diagnostics

[AlaeddineMessadi]

OpenCode V2 changes session, input, permission and lifecycle contracts, so routing existing V1 tools directly to it cannot preserve their behavior. This adds typed V1/V2 adapters, backend detection, read-only diagnostics, normalized operations, durable V2 jobs and native MCP Tasks while preserving V1 support.

The capability manifest accounts for 87 tools plus resources/templates/prompts. V2 has 64 supported mappings, 22 intentional V1-only exceptions, and one upstream-blocked command operation. Unsupported calls fail before mutation. Setup/migration docs, generated compatibility references, production archive checks, and Ubuntu/macOS/Windows × Node 22/24 CI are included. Package metadata is prepared as 3.1.0-rc.1; nothing has been published.

Validation

• Full local suites: 755 passed, 3 skipped on Node 22.23.2 and 24.21.0 (macOS arm64).
• Coverage gate passed; generated documentation and whitespace checks passed; npm audit reports zero vulnerabilities.
• Retained candidate archive passed production installation checks and model-free native checks against opencode-ai@1.18.31 and @opencode/cli@2.0.6 on both Node versions.
• Live doctor checks verified read-only requests, no startup attempts, accurate provider readiness, and credential redaction.

Why this is a draft

• opencode_command_execute remains blocked by missing V2 invocation/result correlation: [FEATURE]: V2 session.command invocation identity and result correlation anomalyco/opencode#49690. The original 65-supported-tool milestone gate is not met.
• Durable execution/recovery, forms/permissions, reverts and native Tasks have fixture/contract coverage; live inference, OAuth and GUI clients remain unverified. Hosted-platform CI results are pending.
• One initial V2 native-test final-phase failure did not reproduce on subsequent runs. Its cause remains unresolved; the harness now distinguishes cleanup failures and records safe failure diagnostics.

See plans/verification.md for exact evidence, plans/004-v2-writes-input.md for the unblock checklist, and MIGRATION.md for option and lifecycle limitations.

[brocasm]

Interressing about this PR, wainting merge to test this MCP