diff --git a/scripts/ensure-source-resources.cjs b/scripts/ensure-source-resources.cjs
index a857ee2b9..ce164d750 100644
--- a/scripts/ensure-source-resources.cjs
+++ b/scripts/ensure-source-resources.cjs
@@ -90,3 +90,71 @@ if (shouldRebuild()) {
 		process.exit(result.status ?? 1);
 	}
 }
+
+/**
+ * Auto-rebuild workspace packages whose src/ is newer than dist/.
+ *
+ * Without this, edits to packages/coding-agent/src/* (or any other workspace
+ * package src) silently land while the dist stays stale — agents continue
+ * loading the old compiled JS and operators see "why didn't my edit take
+ * effect?" symptoms (observed 2026-05-17 with the AST tools wire-in).
+ *
+ * Skipped:
+ *   - native: Rust build takes 5–10 min; trigger manually via
+ *     `node rust-engine/scripts/build.js --dev` instead.
+ *   - any package set in SF_SKIP_WORKSPACE_AUTOBUILD (comma-separated names).
+ *
+ * Override the whole step with SF_SKIP_WORKSPACE_AUTOBUILD=all.
+ */
+const WORKSPACE_AUTOBUILD_PACKAGES = [
+	"agent-core",
+	"ai",
+	"coding-agent",
+	"daemon",
+	"google-gemini-cli-provider",
+	"openai-codex-provider",
+	"rpc-client",
+	"tui",
+];
+
+function packageNeedsRebuild(pkgName) {
+	const pkgDir = join(root, "packages", pkgName);
+	const pkgSrc = join(pkgDir, "src");
+	const pkgDist = join(pkgDir, "dist");
+	if (!existsSync(pkgSrc) || !existsSync(pkgDist)) return false;
+	const srcMtime = latestMtimeMs(pkgSrc);
+	const distMtime = latestMtimeMs(pkgDist);
+	// Add a small grace window so files written within the same second as a
+	// dist sync don't trigger redundant rebuilds.
+	return srcMtime > distMtime + 100;
+}
+
+function rebuildWorkspacePackagesIfStale() {
+	const skip = (process.env.SF_SKIP_WORKSPACE_AUTOBUILD || "")
+		.split(",")
+		.map((s) => s.trim())
+		.filter(Boolean);
+	if (skip.includes("all")) return;
+
+	const stale = WORKSPACE_AUTOBUILD_PACKAGES.filter(
+		(pkg) => !skip.includes(pkg) && packageNeedsRebuild(pkg),
+	);
+	if (stale.length === 0) return;
+
+	console.error(
+		`[forge] Workspace src newer than dist for: ${stale.join(", ")} — rebuilding...`,
+	);
+	for (const pkg of stale) {
+		const result = spawnSync(
+			"npm",
+			["run", "build", "-w", `@singularity-forge/${pkg}`],
+			{ cwd: root, stdio: "inherit", env: process.env },
+		);
+		if (result.status !== 0) {
+			console.error(`[forge] FAILED to rebuild packages/${pkg}`);
+			process.exit(result.status ?? 1);
+		}
+	}
+}
+
+rebuildWorkspacePackagesIfStale();