Open an agentdeck issue

Issues are implementation-ready specifications. Be concise, precise, and dense with signal.

Issue Structure

## Problem
What is broken or missing, and why it matters. For bugs: exact traceback and minimal reproduction steps.

## Proposed shape
The clean, user-intent API or behavior with minimal code snippets. Show the simplest path with zero leaked plumbing. Explicitly state what is out of scope. For a feature, answer Q4 here (`docs/engineering/principles.md`): is this absorbing complexity, or transferring it to the user? That is the question we most often fail, and proposal time is when it is cheapest to fail it.

## Notes
Constraints, affected modules, existing patterns to follow, related issues/PRs.

## Pitfalls
Known failure modes, each backed by evidence.

## Must not
Explicit scope boundaries.

## Done when
Checklist of observable, testable behaviors (mapping 1:1 to deterministic tests without live model calls).

Rules

• Anti-verbosity: Avoid fluff and rambling rationale. One clear sentence beats a paragraph.
• Title: Terse and specific: <area>: <what> (e.g., runtime: propagate cancellation to subagents).
• Single concern: One issue per topic; split unrelated asks.
• Check duplicates: gh issue list --state open.
• Labels: Select one type label (bug, enhancement, feature, chore, design, documentation, or finding) and the closest area:* label from gh label list.
• Output limits: Keep text between tool calls to ≤25 words. Keep final responses to ≤100 words unless more detail is required.
• Create via gh issue create -t <title> -b <body> --label <type> --label <area> and verify the resulting issue has both labels before returning its URL.