feat(adapters): add LangChain export adapter & runner with multi-provider support

paper/tables/fidelity-matrix.csv

@@ -13,4 +13,5 @@ nanobot,F,F,P,F,F,P,P,-,-
 copilot,F,F,P,P,P,-,-,-,-
 github,F,F,P,P,F,-,-,-,P
 gitclaw,F,F,F,F,F,F,F,F,F
+langchain,F,F,F,F,P,-,P,F,P
 system-prompt,F,F,P,P,-,-,-,-,-

src/adapters/index.ts

@@ -11,3 +11,4 @@ export { exportToGeminiString, exportToGemini } from './gemini.js';
 export { exportToCodexString, exportToCodex } from './codex.js';
 export { exportToKiroString, exportToKiro } from './kiro.js';
 export { exportToGitclawString, exportToGitclaw } from './gitclaw.js';
+export { exportToLangChainString } from './langchain.js';

src/adapters/langchain-utils.ts

@@ -0,0 +1,22 @@
+export interface ProviderInfo {
+  provider: string;
+  pipPackage: string;
+  envVar: string;
+}
+
+/**
+ * Maps a model name to its LangChain provider info.
+ * Returns null for unsupported models.
+ *
+ * OpenAI coverage: gpt-* and o<digit>-* (o1, o3, o4-mini, …)
+ * Anthropic coverage: claude-*
+ */
+export function detectProvider(model: string): ProviderInfo | null {
+  const m = model.toLowerCase();
+  if (m.startsWith('claude'))
+    return { provider: 'anthropic', pipPackage: 'langchain-anthropic', envVar: 'ANTHROPIC_API_KEY' };
+  // Matches gpt-* and OpenAI reasoning models: o1, o3, o4-mini, etc.
+  if (m.startsWith('gpt') || /^o\d/.test(m))
+    return { provider: 'openai', pipPackage: 'langchain-openai', envVar: 'OPENAI_API_KEY' };
+  return null;
+}