From 2c588d8750ea671e08bc163e4ebbb266ad14b05e Mon Sep 17 00:00:00 2001
From: can1357 <me@can.ac>
Date: Thu, 20 Aug 2026 06:36:43 +0200
Subject: [PATCH] docs(extensions): documented composer shape renderer and
 styling contract

- Document the `registerComposerShape` API method for adding input-editor layouts.
- Detail the `ComposerStyle` layout metadata properties and rendering methods.
- Provide a full implementation example demonstrating custom composer styling and registration.
---
 docs/extensions.md | 76 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 76 insertions(+)

diff --git a/docs/extensions.md b/docs/extensions.md
index 9b67b972d..09208fcc8 100644
--- a/docs/extensions.md
+++ b/docs/extensions.md
@@ -115,6 +115,7 @@ Core methods:
 - `on(event, handler)`
 - `registerTool`, `registerCommand`, `registerShortcut`, `registerFlag`
 - `registerMessageRenderer`, `registerAssistantThinkingRenderer`
+- `registerComposerShape`
 - `setLabel`, `getFlag`
 - `sendMessage`, `sendUserMessage`, `appendEntry`, `exec`
 - `getActiveTools`, `getAllTools`, `setActiveTools`
@@ -576,6 +577,81 @@ pi.on("session_start", async (_event, ctx) => {
 
 ## Rendering extension points
 
+## Composer shape renderer
+
+`registerComposerShape` adds an extension-owned input-editor layout to **Appearance → Composer Shape**. Register it from the extension factory; the renderer is used by the live editor and its settings preview.
+
+```ts
+import type { ExtensionAPI } from "@oh-my-pi/pi-coding-agent";
+import type { ComposerStyle } from "@oh-my-pi/pi-tui";
+
+const dockStyle: ComposerStyle = {
+  id: "acme-dock",
+  sideBorders: false,
+  verticalChrome: 1,
+  statusAttachment: "none",
+  bottomBar: "full",
+  bottomBarGap: true,
+  defaultPromptGutter: "❯ ",
+
+  defaultPaddingX: () => 0,
+  sideChromeWidth: () => 0,
+  renderTop: ({ box, width, borderColor }) =>
+    borderColor(box.horizontal.repeat(width)),
+  renderRow: ({ gutter, text, pad }) => [gutter + text + pad],
+  renderBottom: () => undefined,
+};
+
+export default function (pi: ExtensionAPI) {
+  pi.registerComposerShape({
+    label: "Acme Dock",
+    description: "Prompt below a single rule",
+    style: dockStyle,
+  });
+}
+```
+
+`ComposerShapeDefinition` contains:
+
+- `label`: required selector label.
+- `description`: optional selector detail.
+- `style`: the complete `ComposerStyle` rendering contract. `style.id` is also the persisted `composer.shape` value.
+
+Use a package-qualified, non-empty, trimmed `style.id`. Built-in ids (`box`, `claude`, `pi`, `borderless`, `rule`, `field`, and `rail`) cannot be replaced. If the extension is unavailable while its id remains configured, the editor falls back to `box`.
+
+### `ComposerStyle` layout metadata
+
+- `sideBorders`: whether content rows own side chrome. This controls cursor reserve, IME layout, and scrollbar behavior; it is not merely descriptive.
+- `verticalChrome`: exact number of fixed top/bottom chrome rows (`0`, `1`, or `2`) used for editor height budgeting.
+- `statusAttachment`: `"top-border"` receives the embedded status gauge, `"top-rule-chip"` receives the right status group for docking on a rule, and `"none"` detaches status from the editor chrome.
+- `bottomBar`: standalone status content below the editor: `"none"`, `"left"`, or `"full"`.
+- `bottomBarGap`: whether a blank row separates the editor from a standalone bottom status bar.
+- `defaultPromptGutter`: prompt text used when the host supplies no override.
+- `defaultPaddingX(themePaddingX)`: horizontal padding selected for this style.
+- `sideChromeWidth(paddingX)`: visible cells consumed on **each** side of a content row, including padding and border/rail glyphs.
+
+`renderTop` and `renderBottom` return one styled terminal row or `undefined`. `renderRow` returns one or more styled rows. Every normal rendered row must occupy exactly `ctx.width` visible cells; ANSI escape sequences have zero width. Preserve the supplied `gutter`, `text`, and `pad` instead of reflowing or truncating them.
+
+### Renderer context
+
+All render methods receive `width`, `paddingX`, the theme's `box` glyphs, and three styling functions:
+
+- `borderColor(text)`: ordinary frame/rule color.
+- `accentColor(text)`: stable accent for shape-defining rails or caps.
+- `surfaceColor(text)`: composer background fill that survives nested SGR resets in decorated input.
+
+`topBorder`, when present, is already-styled status content with its visible `width`. A top renderer owns its placement and must leave the final line at `ctx.width`.
+
+`renderRow` additionally receives:
+
+- `gutter`, `text`, and `pad`: pre-rendered content pieces.
+- `isLastRow`: last visible input row.
+- `cursorOverflow`: cells consumed from the right chrome by an end-of-line cursor.
+- `imeSafeCursorTail`: omit right-side cells after the cursor so terminal-local IME preedit cannot shift the chrome.
+- `scrollbarThumb`: this row intersects the editor scrollbar thumb.
+
+The built-in implementations in `packages/tui/src/components/composer/` are the reference for framed, rule, filled-surface, and IME-safe layouts.
+
 ## Custom message renderer
 
 ```ts