feat(x): configurable model-call limits by workflow (#768)

Replace the hardcoded 20-call turn budget with user settings: a global
model-call limit that every turn inherits (headless/knowledge work,
scheduled agents, sub-agents) plus an optional chat-only override for
interactive turns. Settings live in config/turn_limits.json (1-100,
default 20) and are edited from a new Advanced tab in Settings.

The limit is resolved at turn creation via an ITurnLimitsResolver
injected into TurnRuntime, keyed on humanAvailable; explicit per-call
overrides still win, and the resolved value is persisted in
turn_created.config.maxModelCalls as before, so historical and
in-flight turns are unaffected by settings changes. Sub-agents now
default to and are capped by the global limit instead of the constant.

apps/x/packages/shared/src/index.ts

@@ -19,6 +19,7 @@ export * as browserControl from './browser-control.js';
 export * as billing from './billing.js';
 export * as credits from './credits.js';
 export * as notificationSettings from './notification-settings.js';
+export * as turnLimits from './turn-limits.js';
 export * as codeSessions from './code-sessions.js';
 export * as channels from './channels.js';
 export * as rowboatApp from './rowboat-app.js';

apps/x/packages/shared/src/ipc.ts

@@ -25,6 +25,7 @@ import { CreditActivatedEventSchema, CreditsStateSchema, ReferralClaimResultSche
 import { EmailBlockSchema, GmailThreadSchema } from './blocks.js';
 import { PermissionDecision, ApprovalPolicy, CodingAgent, type CodeRunFeedEvent } from './code-mode.js';
 import { NotificationSettingsSchema } from './notification-settings.js';
+import { TurnLimitsSettingsSchema } from './turn-limits.js';
 import { CodeProject, CodeSession, CodeSessionMode, CodeSessionStatus, GitRepoInfo, GitStatusFile, CodeAgentModelOptions } from './code-sessions.js';
 import { ChannelsConfig, ChannelsStatus } from './channels.js';
 
@@ -2455,6 +2456,17 @@ const ipcSchemas = {
       success: z.literal(true),
     }),
   },
+  // Model-call limit settings channels
+  'turnLimits:getSettings': {
+    req: z.null(),
+    res: TurnLimitsSettingsSchema,
+  },
+  'turnLimits:setSettings': {
+    req: TurnLimitsSettingsSchema,
+    res: z.object({
+      success: z.literal(true),
+    }),
+  },
 } as const;
 
 // ============================================================================

apps/x/packages/shared/src/turn-limits.ts

@@ -0,0 +1,34 @@
+import { z } from 'zod';
+import { DEFAULT_MAX_MODEL_CALLS } from './turns.js';
+
+/**
+ * User-configurable model-call budgets (see issue #768).
+ *
+ * - maxModelCalls: the global limit every turn inherits by default,
+ *   including headless/knowledge work and spawned sub-agents (it is also
+ *   the cap a parent can grant a sub-agent).
+ * - chatMaxModelCalls: optional override for interactive chat turns only;
+ *   when absent, chat uses the global limit.
+ *
+ * Changing these affects only newly created turns — each turn persists its
+ * resolved limit in turn_created.config.maxModelCalls.
+ */
+export const MIN_MODEL_CALL_LIMIT = 1;
+export const MAX_MODEL_CALL_LIMIT = 100;
+
+const limit = z
+  .number()
+  .int()
+  .min(MIN_MODEL_CALL_LIMIT)
+  .max(MAX_MODEL_CALL_LIMIT);
+
+export const TurnLimitsSettingsSchema = z.object({
+  maxModelCalls: limit,
+  chatMaxModelCalls: limit.optional(),
+});
+
+export const DEFAULT_TURN_LIMITS_SETTINGS: TurnLimitsSettings = {
+  maxModelCalls: DEFAULT_MAX_MODEL_CALLS,
+};
+
+export type TurnLimitsSettings = z.infer<typeof TurnLimitsSettingsSchema>;