Before you begin, read quest/AGENTS.md completely.
Interview the user relentlessly until you reach a shared understanding. Begin the interview by scoping the goal: the observable outcome, why it matters, and its important boundaries and non-goals. Do not move on to implementation decisions until the goal is settled. If the goal contains independently completable outcomes, split them before planning.
Then map the implementation plan as a design tree: every material decision branches into the decisions that hang off it.
Work the tree in rounds. The frontier is every decision whose prerequisites are already settled: the questions you can ask now without guessing at answers you haven't heard yet. Ask the whole frontier in one round, interactively if supported: number each question, letter each answer, and prefix one answer with (recommended). Then wait for the user's answers before the next round.
Each round the user answers reshapes the tree: settled decisions push the frontier outward and unblock questions that depended on them. Recompute the frontier and ask the next round. A question whose answer depends on another question still open in this round belongs to a later round, not this one.
Finding facts is your job, never the user's. When a frontier question needs a fact from the environment (filesystem, tools, etc.), dispatch a sub-agent to find it; don't ask the user for anything you could look up yourself. Don't block on it: a running exploration is an unsettled prerequisite, so only the questions downstream of it wait for the sub-agent to report; ask the rest of the frontier now. The decisions are the user's: put each to them and wait.
Search other quests and questlines to keep the larger plan consistent. When the frontier disagrees with a settled quest, challenge the user and ask whether to expand scope to resolve the conflict.
The session is done when the frontier is empty: every branch of the design tree visited, nothing left silently assumed.
The result may be one quest or multiple quests and questlines. Split outcomes that can be completed independently.
Prefix each quest title with [XS], [S], [M], [L], or [XL], including implementation, verification, and landing work.
Once complete, create, update, or delete the relevant quests and questlines.
Commit and make a PR, then offer to start working on the quest now if it is ready.