Add markdown-body-color extension — color unwrapped markdown paragraphs

pi-tui's Markdown component only colors paragraph text when the caller
passes a defaultTextStyle.color wrapper. Pi-coding-agent does this for
thinking blocks but not for regular assistant content, so paragraphs
emit uncoloured and inherit the terminal profile's foreground color
(green on many themes).

This extension monkey-patches Markdown.prototype.render to install a
fallback defaultTextStyle (inkPurple #d4c5e8 by default, overridable
via PI_MARKDOWN_BODY_COLOR) when one isn't already set. Thinking blocks
and other custom-colored markdowns are untouched.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitignore

@@ -10,6 +10,7 @@
 !/README.md
 !/ai-server/
 !/local-llama.ts
+!/markdown-body-color.ts
 !/mechanicus-banner.ts
 !/scripts/
 !/themes/

markdown-body-color.ts

@@ -0,0 +1,63 @@
+/**
+ * markdown-body-color — force a theme-aware color on markdown paragraph text.
+ *
+ * Why: pi-tui's Markdown component only wraps paragraph text in a color when
+ * the caller passes a `defaultTextStyle.color` fn (assistant-message.js does
+ * this for thinking blocks but not for regular assistant content). Without it,
+ * paragraph output is emitted uncoloured and inherits the terminal profile's
+ * foreground color — which on many terminal themes is green.
+ *
+ * Fix: monkey-patch Markdown.prototype.render so that if no defaultTextStyle
+ * is set at render time, we install one that wraps output in the active pi
+ * theme's `text` token color. This leaves thinking blocks and custom-colored
+ * markdowns alone (they already have their own defaultTextStyle).
+ */
+
+import type { ExtensionAPI } from "@mariozechner/pi-coding-agent";
+import { Markdown } from "@mariozechner/pi-tui";
+
+// Hardcoded fallback — matches themes/dark-mechanicus.json "inkPurple" var.
+// Override via PI_MARKDOWN_BODY_COLOR env var (hex, e.g. "#d4c5e8").
+const FALLBACK_HEX = process.env.PI_MARKDOWN_BODY_COLOR ?? "#d4c5e8";
+
+function hexToRgb(hex: string): [number, number, number] {
+	const m = hex.replace(/^#/, "");
+	const n = parseInt(m.length === 3
+		? m.split("").map((c) => c + c).join("")
+		: m, 16);
+	return [(n >> 16) & 0xff, (n >> 8) & 0xff, n & 0xff];
+}
+
+const [R, G, B] = hexToRgb(FALLBACK_HEX);
+const OPEN = `\x1b[38;2;${R};${G};${B}m`;
+const CLOSE = `\x1b[39m`;
+
+function wrapWithBodyColor(text: string): string {
+	// Re-open the color after any existing `\x1b[39m` (default-fg reset) so
+	// nested styled runs inside a paragraph don't bleed back to terminal fg.
+	const safe = text.split(CLOSE).join(CLOSE + OPEN);
+	return OPEN + safe + CLOSE;
+}
+
+let patched = false;
+
+export default function (_pi: ExtensionAPI) {
+	if (patched) return;
+	patched = true;
+
+	const proto = Markdown.prototype as any;
+	const originalRender = proto.render;
+
+	proto.render = function (width: number) {
+		if (!this.defaultTextStyle) {
+			this.defaultTextStyle = { color: wrapWithBodyColor };
+			// Force cache invalidation so the first post-patch render colors content.
+			if (typeof this.invalidate === "function") this.invalidate();
+		}
+		return originalRender.call(this, width);
+	};
+
+	console.log(
+		`[markdown-body-color] Default markdown body color = ${FALLBACK_HEX}`,
+	);
+}