fix: pause compatibility commands before admission

[danyel117]

Summary

• enforce /pause_goal at the V2 prompt-admission boundary when OpenCode executes the V1-compatible static command definition instead of the V2 command executor
• sanitize appended arguments and attachments for both static /pause_goal and /resume_goal prompts
• keep resume model-mediated so existing Plan-mode enforcement remains authoritative
• register/dispose the fallback only when command registration is enabled
• add a regression reproducing the real V1-command/V2-runtime order and cleanup assertions

Reproduction

After installing 0.1.43, an OpenCode V2 standalone smoke showed /pause_goal calling get_goal while the goal was still active; it only became paused after the model called update_goal_status. With this change loaded from dist/server.js, the model context already observes the paused goal and no active-state get_goal occurs.

Verification

• bun run lint
• bun run typecheck
• bun test (231 passing)
• bun run build
• bun run pack:dry-run
• real OpenCode V2 v0.0.0-beta-18593 standalone smoke with isolated goal state
• internal correctness review: approved
• internal standards review: approved

Follow-up to #36 and #44.

AI assistance: diagnosed from an end-to-end smoke, implemented, and reviewed with OpenCode agents; an independent Claude Opus review will be attached before merge.

[danyel117]

Claude Opus independent review: APPROVE.

No merge-blocking findings. Opus verified the V2 SessionPrompt mutability contract, complete attachment sanitization, full-template ownership check, idempotence with native command executors, lifecycle/race guards, Plan-mode resume behavior, register_command: false, disposal, regression quality, 231 tests, lint, typecheck, package contents, and byte-for-byte reproducibility of dist/server.js.

Residual risks are non-blocking: template-format coupling to beta-18593 and a pre-existing narrow close-vs-pause TOCTOU shared by all pause paths.