Bug: Completion Gate false-positive for non-code tasks (issue filing, git push, etc.)

[tianxingzhivlog-droid]

Bug Description

The evaluateCompletionGate in drift-guard.js always checks for verification type entries in the evidence ledger. However, for non-code tasks like filing issues, pushing code, or answering questions, there is no test to run — the task completion IS the verification. This causes persistent Warning: Completion gate missing warnings throughout the session.

Reproduction

1. Start OpenHorse
2. Ask it to file a GitHub issue (e.g., 提issue给官方)
3. Issue is successfully created (verified by gh cli output)
4. Context Harness still reports: Warning: Completion gate missing: Required verification has not passed yet.

Root Cause

drift-guard.js:evaluateCompletionGate() hardcodes the requirement for verification evidence, without distinguishing task types:

// Always requires verification evidence, regardless of task nature
const hasVerification = ledgerEntries.some(e => e.type === "verification");

Expected Behavior

• For code tasks: require test/verification evidence (current behavior)
• For non-code tasks (issue filing, git push, Q&A): consider the tool success output as sufficient verification
• Or: allow the agent to mark a task as "verification not applicable"

Suggested Fix

Add a verificationType field to the task contract:

• "test" — requires test evidence (default for code tasks)
• "tool_success" — tool output with exit code 0 is sufficient (for issue filing, push, etc.)
• "none" — no verification needed (for Q&A)

Environment

• OpenHorse: v0.2.24
• Node.js: v22.23.1
• macOS Darwin