Update CHANGELOG with CustomMessageEntry and hook rendering API

packages/coding-agent/CHANGELOG.md

@@ -27,8 +27,13 @@
   - `before_switch` event now has `targetSessionFile`, `switch` event has `previousSessionFile`
   - Removed `resolveApiKey` (use `modelRegistry.getApiKey(model)`)
   - Hooks can return `compaction.details` to store custom data (e.g., ArtifactIndex for structured compaction)
+- **Hook API**:
+  - New `pi.renderCustomMessage(customType, renderer)` to register custom renderers for `CustomMessageEntry`
+  - `CustomMessageRenderer` type: `(entry, options, theme) => Component | null`
+  - Renderers return inner content; the TUI wraps it in a styled Box
 - **SessionManager**:
   - `getSessionFile()` now returns `string | undefined` (undefined for in-memory sessions)
+- **Themes**: Custom themes must add `customMessageBg`, `customMessageText`, `customMessageLabel` color tokens
 
 ### Added
 
@@ -38,8 +43,9 @@
 
 - **Entry IDs**: Session entries now use short 8-character hex IDs instead of full UUIDs
 - **API key priority**: `ANTHROPIC_OAUTH_TOKEN` now takes precedence over `ANTHROPIC_API_KEY`
-- **New entry types**: `BranchSummaryEntry` for branch context, `CustomEntry<T>` for hook state persistence, `LabelEntry` for user-defined bookmarks
+- **New entry types**: `BranchSummaryEntry` for branch context, `CustomEntry<T>` for hook state persistence, `CustomMessageEntry<T>` for hook-injected context messages, `LabelEntry` for user-defined bookmarks
 - **Entry labels**: New `getLabel(id)` and `appendLabelChange(targetId, label)` methods for labeling entries. Labels are included in `SessionTreeNode` for UI/export.
+- **TUI**: `CustomMessageEntry` renders with purple styling (customMessageBg, customMessageText, customMessageLabel theme colors). Entries with `display: false` are hidden.
 
 ### Fixed
 

packages/coding-agent/src/modes/interactive/components/custom-message.ts

@@ -0,0 +1,58 @@
+import type { TextContent } from "@mariozechner/pi-ai";
+import { Box, Container, Markdown, Spacer, Text } from "@mariozechner/pi-tui";
+import type { CustomMessageRenderer } from "../../../core/hooks/types.js";
+import type { CustomMessageEntry } from "../../../core/session-manager.js";
+import { getMarkdownTheme, theme } from "../theme/theme.js";
+
+/**
+ * Component that renders a custom message entry from hooks.
+ * Uses distinct styling to differentiate from user messages.
+ */
+export class CustomMessageComponent extends Container {
+	constructor(entry: CustomMessageEntry, customRenderer?: CustomMessageRenderer) {
+		super();
+
+		this.addChild(new Spacer(1));
+
+		// Create box with purple background
+		const box = new Box(1, 1, (t) => theme.bg("customMessageBg", t));
+
+		// Try custom renderer first
+		if (customRenderer) {
+			try {
+				const component = customRenderer(entry, { expanded: false }, theme);
+				if (component) {
+					box.addChild(component);
+					this.addChild(box);
+					return;
+				}
+			} catch {
+				// Fall through to default rendering
+			}
+		}
+
+		// Default rendering: label + content
+		const label = theme.fg("customMessageLabel", `\x1b[1m[${entry.customType}]\x1b[22m`);
+		box.addChild(new Text(label, 0, 0));
+		box.addChild(new Spacer(1));
+
+		// Extract text content
+		let text: string;
+		if (typeof entry.content === "string") {
+			text = entry.content;
+		} else {
+			text = entry.content
+				.filter((c): c is TextContent => c.type === "text")
+				.map((c) => c.text)
+				.join("\n");
+		}
+
+		box.addChild(
+			new Markdown(text, 0, 0, getMarkdownTheme(), {
+				color: (text: string) => theme.fg("customMessageText", text),
+			}),
+		);
+
+		this.addChild(box);
+	}
+}