speckit-iterate-definelisted

## User Input ```text $ARGUMENTS ``` You **MUST** consider the user input before proceeding (if not empty). The text the user typed after `/speckit.iterate.define` **is** the change request. It describes what should be added, modified, or removed from the current feature — either the whole feature or a specific phase/subtask. ## Outline Goal: Analyze a requested change against the feature's current spec state and implementation progress, then produce a reviewable iteration plan written to `pending-iteration.md`. This command does **not** modify any spec artifacts — it only writes the pending iteration file. ### 1. Initialize Feature Context Run `.specify/scripts/bash/check-prerequisites.sh --json --paths-only` from repo root **once**. Parse JSON payload fields: - `FEATURE_DIR` - `FEATURE_SPEC` - (Optionally capture `IMPL_PLAN`, `TASKS` for downstream use.) If JSON parsing fails, abort and instruct the user to run `/speckit.specify` or verify the feature branch environment. For single quotes in args like "I'm Groot", use escape syntax: e.g 'I'\''m Groot' (or double-quote if possible: "I'm Groot"). ### 2. Check for Existing Pending Iteration Check if `FEATURE_DIR/pending-iteration.md` already exists. If it does: - Warn the user: "A pending iteration already exists. Running define again will overwrite it." - Show the existing file's `change_request` and `created` date from its frontmatter. - Ask the user to confirm before proceeding, or suggest running `/speckit.ite