feat: add CLI backend fallback

src/config/schema.ts

@@ -112,6 +112,7 @@ const FIELD_LABELS: Record<string, string> = {
   "agents.defaults.humanDelay.mode": "Human Delay Mode",
   "agents.defaults.humanDelay.minMs": "Human Delay Min (ms)",
   "agents.defaults.humanDelay.maxMs": "Human Delay Max (ms)",
+  "agents.defaults.cliBackends": "CLI Backends",
   "commands.native": "Native Commands",
   "commands.text": "Text Commands",
   "commands.restart": "Allow Restart",
@@ -191,6 +192,8 @@ const FIELD_HELP: Record<string, string> = {
     "Optional image model (provider/model) used when the primary model lacks image input.",
   "agents.defaults.imageModel.fallbacks":
     "Ordered fallback image models (provider/model).",
+  "agents.defaults.cliBackends":
+    "Optional CLI backends for text-only fallback (claude-cli, etc.).",
   "agents.defaults.humanDelay.mode":
     'Delay style for block replies ("off", "natural", "custom").',
   "agents.defaults.humanDelay.minMs":

src/config/sessions.ts

@@ -113,6 +113,7 @@ export type SessionEntry = {
   model?: string;
   contextTokens?: number;
   compactionCount?: number;
+  cliSessionIds?: Record<string, string>;
   claudeCliSessionId?: string;
   label?: string;
   displayName?: string;

src/config/types.ts

@@ -1355,6 +1355,45 @@ export type AgentContextPruningConfig = {
   };
 };
 
+export type CliBackendConfig = {
+  /** CLI command to execute (absolute path or on PATH). */
+  command: string;
+  /** Base args applied to every invocation. */
+  args?: string[];
+  /** Output parsing mode (default: json). */
+  output?: "json" | "text";
+  /** Prompt input mode (default: arg). */
+  input?: "arg" | "stdin";
+  /** Max prompt length for arg mode (if exceeded, stdin is used). */
+  maxPromptArgChars?: number;
+  /** Extra env vars injected for this CLI. */
+  env?: Record<string, string>;
+  /** Env vars to remove before launching this CLI. */
+  clearEnv?: string[];
+  /** Flag used to pass model id (e.g. --model). */
+  modelArg?: string;
+  /** Model aliases mapping (config model id → CLI model id). */
+  modelAliases?: Record<string, string>;
+  /** Flag used to pass session id (e.g. --session-id). */
+  sessionArg?: string;
+  /** When to pass session ids. */
+  sessionMode?: "always" | "existing" | "none";
+  /** JSON fields to read session id from (in order). */
+  sessionIdFields?: string[];
+  /** Flag used to pass system prompt. */
+  systemPromptArg?: string;
+  /** System prompt behavior (append vs replace). */
+  systemPromptMode?: "append" | "replace";
+  /** When to send system prompt. */
+  systemPromptWhen?: "first" | "always" | "never";
+  /** Flag used to pass image paths. */
+  imageArg?: string;
+  /** How to pass multiple images. */
+  imageMode?: "repeat" | "list";
+  /** Serialize runs for this CLI. */
+  serialize?: boolean;
+};
+
 export type AgentDefaultsConfig = {
   /** Primary model and fallbacks (provider/model). */
   model?: AgentModelListConfig;
@@ -1370,6 +1409,8 @@ export type AgentDefaultsConfig = {
   userTimezone?: string;
   /** Optional display-only context window override (used for % in status UIs). */
   contextTokens?: number;
+  /** Optional CLI backends for text-only fallback (claude-cli, etc.). */
+  cliBackends?: Record<string, CliBackendConfig>;
   /** Opt-in: prune old tool results from the LLM context to reduce token usage. */
   contextPruning?: AgentContextPruningConfig;
   /** Default thinking level when no /think directive is present. */

src/config/zod-schema.ts

@@ -124,6 +124,33 @@ const HumanDelaySchema = z.object({
   maxMs: z.number().int().nonnegative().optional(),
 });
 
+const CliBackendSchema = z.object({
+  command: z.string(),
+  args: z.array(z.string()).optional(),
+  output: z.union([z.literal("json"), z.literal("text")]).optional(),
+  input: z.union([z.literal("arg"), z.literal("stdin")]).optional(),
+  maxPromptArgChars: z.number().int().positive().optional(),
+  env: z.record(z.string(), z.string()).optional(),
+  clearEnv: z.array(z.string()).optional(),
+  modelArg: z.string().optional(),
+  modelAliases: z.record(z.string(), z.string()).optional(),
+  sessionArg: z.string().optional(),
+  sessionMode: z
+    .union([z.literal("always"), z.literal("existing"), z.literal("none")])
+    .optional(),
+  sessionIdFields: z.array(z.string()).optional(),
+  systemPromptArg: z.string().optional(),
+  systemPromptMode: z
+    .union([z.literal("append"), z.literal("replace")])
+    .optional(),
+  systemPromptWhen: z
+    .union([z.literal("first"), z.literal("always"), z.literal("never")])
+    .optional(),
+  imageArg: z.string().optional(),
+  imageMode: z.union([z.literal("repeat"), z.literal("list")]).optional(),
+  serialize: z.boolean().optional(),
+});
+
 const normalizeAllowFrom = (values?: Array<string | number>): string[] =>
   (values ?? []).map((v) => String(v).trim()).filter(Boolean);
 
@@ -1037,6 +1064,7 @@ const AgentDefaultsSchema = z
     skipBootstrap: z.boolean().optional(),
     userTimezone: z.string().optional(),
     contextTokens: z.number().int().positive().optional(),
+    cliBackends: z.record(z.string(), CliBackendSchema).optional(),
     contextPruning: z
       .object({
         mode: z