Loop exits silently on orphaned interrupted tool — prompt stays unanswered

When a tool call is cut mid-stream (provider emits tool-input-start without a complete tool-call then drops the connection), the agent loop silently exits without answering the prompt.

Repro:

• Mock OpenAI-compatible provider that streams a tool announcement with incomplete arguments then cuts mid-stream
• opencode retries; retried request completes with empty finish: "stop"
• processor.cleanup() marks the in-flight tool as:

{"type":"tool","tool":"read","callID":"call_orphan_1","state":{"status":"error","input":{},"error":"Tool execution aborted","metadata":{"interrupted":true},"time":{"start":1787392868553,"end":1787392868553}}}

• Run loop logs:

WARN loop exit with orphaned interrupted tool session.id=ses_... messageID=msg_... tool=read callID=call_orphan_1
INFO exiting loop session.id=ses_...

• Persisted assistant message has no text, zero tokens, time.start == time.end. Prompt stays unanswered, no error surfaced, interrupted tool never fed back as tool_result so model cannot self-correct.

Root cause:

• packages/opencode/src/session/processor.ts:cleanup() force-marks abandoned tool as interrupted:true
• packages/opencode/src/session/prompt.ts excludes orphaned interrupted tools from hasToolCalls → message judged finished → loop breaks

Expected:
Treat interrupted:true as recoverable tool error: feed Tool execution aborted — please retry with complete arguments back as tool_result and retry (with limit), or after retries emit a user-visible assistant error. Never exit silently with zero tokens.

Also seen: short sessions (83 parts / 113k tokens) and stealth/oxalpha + muse-spark families; also step-finish reason:unknown with zero tokens after Service Unavailable on retry — same silent-exit family.

Verified on: opencode 1.18.21 Linux (and 1.3.13 macOS)