Fix Windows OpenCode JSON capability false negatives

[CompleteDotTech]

What changed

• preserve a recently verified OpenCode JSON capability only when a new Windows help probe is transiently unavailable
• bind that fallback to the familiar scope, launcher fingerprint, reported version, and a 60-second lifetime
• distinguish an unavailable capability probe from a confirmed lack of JSON support, avoiding a false error issue in progress UI

Why

PowerShell/npm launcher cold starts or transient failures can leave opencode run --help incomplete. The previous implementation treated this lack of evidence as proof that JSON was unsupported, disabling tool activity even when the installed client supports --format json.

Impact

Windows users retain structured OpenCode tool activity across a short transient probe failure when the same launcher was just verified. New, changed, expired, or unverified launchers still fail closed to plain chat.

Validation

• chat-send-capabilities.test.ts
• opencode-compatibility.test.ts
• harness-routing-opencode.test.ts
• live capability check against installed OpenCode 1.18.5: verified JSON support resolves to opencode-run-json-v1