F3 SLICE-5: live claude-code turn via applyAgentEdit seam + manual smoke (INV-8) (#6)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/liveTurn.ts

@@ -0,0 +1,57 @@
+/**
+ * LiveTurn — the minimal machine-edit ingress (spec §6.2): one @cline/sdk
+ * Agent turn on the built-in `claude-code` provider, which rides the
+ * operator's local Claude Code Pro/Max login — the extension holds NO
+ * credentials of any kind (INV-8). vscode-free; the editSelection command
+ * (extension.ts) feeds the result into the applyAgentEdit seam (INV-9).
+ *
+ * Like src/cline.ts: @cline/sdk is ESM-only, loaded via dynamic import(),
+ * never bundled (esbuild keeps it external).
+ */
+
+export interface EditTurnResult {
+  replacement: string;
+  model: string;
+  /** the SDK run id — recorded as provenance sessionId. */
+  sessionId: string;
+}
+
+const SYSTEM_PROMPT = [
+  "You are a precise text editor embedded in VS Code.",
+  "You will be given a piece of text and an instruction.",
+  "Respond with ONLY the edited replacement text — no explanation, no preamble,",
+  "no markdown code fences. Preserve the original's leading/trailing whitespace",
+  "unless the instruction says otherwise.",
+].join(" ");
+
+/** Strip a wrapping markdown code fence if the model added one anyway. */
+export function extractReplacement(outputText: string): string {
+  const m = outputText.match(/^\s*```[^\n]*\n([\s\S]*?)\n?```\s*$/);
+  return m ? m[1] : outputText;
+}
+
+export async function runEditTurn(
+  instruction: string,
+  selectedText: string,
+  opts?: { modelId?: string },
+): Promise<EditTurnResult> {
+  const sdk = await import("@cline/sdk");
+  const modelId = opts?.modelId ?? "sonnet";
+  const agent = new sdk.Agent({
+    providerId: "claude-code",
+    modelId,
+    systemPrompt: SYSTEM_PROMPT,
+  });
+  const result = await agent.run(
+    `<instruction>\n${instruction}\n</instruction>\n<text>\n${selectedText}\n</text>`,
+  );
+  // The SDK's AgentRunResult.status union is "completed" | "aborted" | "failed"
+  // (@cline/shared agent.d.ts) — "completed" is the success status.
+  if (result.status !== "completed") {
+    throw new Error(
+      `claude-code turn ${result.status}: ${result.error?.message ?? "unknown error"} ` +
+        "(is Claude Code installed and signed in?)",
+    );
+  }
+  return { replacement: extractReplacement(result.outputText), model: modelId, sessionId: result.runId };
+}