action-prefix-systemlisted

# Action Prefix System (§11.4.140) A prompt whose **first non-blank line** starts with a registered action token is not an ordinary prompt: the token is **replaced** by that action's registered `expansion` text, the action's `rules` apply, and the remainder of the prompt is the actual task, executed under the expanded instruction. The registry — `constitution/actions/registry.yaml` (override with `$HELIX_ACTION_REGISTRY`) — is the **single source of truth**. It is DATA: adding an action is a registry row, never a code change. ## The six equivalent forms All six resolve to the SAME action, the SAME expansion, the SAME execution: | # | Form | Example | |---|---|---| | 1 | `ACTION :: <rest>` | `BACKGROUND :: refactor the parser` | | 2 | `PREFIX::ACTION :: <rest>` | `DEFAULT::BACKGROUND :: refactor the parser` | | 3 | `/ACTION <rest>` | `/background refactor the parser` | | 4 | `/PREFIX::ACTION <rest>` | `/DEFAULT::BACKGROUND refactor the parser` | | 5 | `ACTION ---> <rest>` | `BACKGROUND ---> refactor the parser` | | 6 | `ACTION: <rest>` — **single colon** | `BUG: subtitles render one frame late` | `PREFIX` is a **namespace**; the reserved default namespace is `DEFAULT`. An action runs with or without it. **Form 6 is the one most people type naturally** (`BUG: ...`, `TASK: ...`) — a colon and exactly one space, no space *before* the colon. ### Form 6 is REGISTERED-ACTION-ONLY by construction Unlike the other five, an unknown single-colon token is a **silent no-op** — it