fix: propagate variant field in all promptAsync continuation paths (#3081)

All 5 continuation paths now send variant as top-level body field:
- boulder-continuation-injector.ts
- ralph-loop/continuation-prompt-injector.ts
- todo-continuation-enforcer/continuation-injection.ts
- unstable-agent-babysitter-hook.ts
- session-recovery/resume.ts

Plus type/helper updates in atlas, todo-continuation-enforcer,
unstable-agent-babysitter, and session-recovery.

TDD: 18 regression tests added, all pass. tsc clean.

src/hooks/unstable-agent-babysitter/index.test.ts

@@ -214,4 +214,45 @@ describe("unstable-agent-babysitter hook", () => {
     expect(promptCalls.length).toBe(1)
     Date.now = originalNow
   })
+
+  test("#given the main session model includes variant #when injecting a babysitter reminder #then promptAsync receives variant as a top-level field", async () => {
+    // given
+    setMainSession("main-1")
+    const promptCalls: Array<{ input: unknown }> = []
+    const mainModel = {
+      providerID: "openai",
+      modelID: "gpt-4",
+      variant: "max",
+    }
+    const ctx = createMockPluginInput({
+      messagesBySession: {
+        "main-1": [
+          { info: { agent: "sisyphus", model: mainModel } },
+        ],
+        "bg-1": [
+          { info: { role: "assistant" }, parts: [{ type: "thinking", thinking: "deep thought" }] },
+        ],
+      },
+      promptCalls,
+    })
+    const backgroundManager = createBackgroundManager([createTask()])
+    const hook = createUnstableAgentBabysitterHook(ctx, {
+      backgroundManager,
+      config: { timeout_ms: 120000 },
+    })
+
+    // when
+    await hook.event({ event: { type: "session.idle", properties: { sessionID: "main-1" } } })
+
+    // then
+    expect(promptCalls.length).toBe(1)
+    const payload = promptCalls[0].input as {
+      body?: {
+        model?: { providerID: string; modelID: string }
+        variant?: string
+      }
+    }
+    expect(payload.body?.model).toEqual({ providerID: "openai", modelID: "gpt-4" })
+    expect(payload.body?.variant).toBe("max")
+  })
 })

src/hooks/unstable-agent-babysitter/task-message-analyzer.ts

@@ -5,7 +5,7 @@ export const THINKING_SUMMARY_MAX_CHARS = 500 as const
 type MessageInfo = {
   role?: string
   agent?: string
-  model?: { providerID: string; modelID: string }
+  model?: { providerID: string; modelID: string; variant?: string }
   providerID?: string
   modelID?: string
   tools?: Record<string, boolean | "allow" | "deny" | "ask">
@@ -33,7 +33,11 @@ export function getMessageInfo(value: unknown): MessageInfo | undefined {
     ? info.model
     : undefined
   const model = modelValue && typeof modelValue.providerID === "string" && typeof modelValue.modelID === "string"
-    ? { providerID: modelValue.providerID, modelID: modelValue.modelID }
+    ? {
+        providerID: modelValue.providerID,
+        modelID: modelValue.modelID,
+        ...(typeof modelValue.variant === "string" ? { variant: modelValue.variant } : {}),
+      }
     : undefined
   return {
     role: typeof info.role === "string" ? info.role : undefined,

src/hooks/unstable-agent-babysitter/unstable-agent-babysitter-hook.ts

@@ -30,6 +30,7 @@ type BabysitterContext = {
         body: {
           parts: Array<{ type: "text"; text: string }>
           agent?: string
+          variant?: string
           model?: { providerID: string; modelID: string }
           tools?: Record<string, boolean>
         }
@@ -40,6 +41,7 @@ type BabysitterContext = {
         body: {
           parts: Array<{ type: "text"; text: string }>
           agent?: string
+          variant?: string
           model?: { providerID: string; modelID: string }
           tools?: Record<string, boolean>
         }
@@ -58,9 +60,9 @@ type BabysitterOptions = {
 async function resolveMainSessionTarget(
   ctx: BabysitterContext,
   sessionID: string
-): Promise<{ agent?: string; model?: { providerID: string; modelID: string }; tools?: Record<string, boolean> }> {
+): Promise<{ agent?: string; model?: { providerID: string; modelID: string; variant?: string }; tools?: Record<string, boolean> }> {
   let agent = getSessionAgent(sessionID)
-  let model: { providerID: string; modelID: string } | undefined
+  let model: { providerID: string; modelID: string; variant?: string } | undefined
   let tools: Record<string, boolean> | undefined
 
   try {
@@ -206,11 +208,17 @@ export function createUnstableAgentBabysitterHook(ctx: BabysitterContext, option
       const { agent, model, tools } = await resolveMainSessionTarget(ctx, mainSessionID)
 
       try {
+        const launchModel = model
+          ? { providerID: model.providerID, modelID: model.modelID }
+          : undefined
+        const launchVariant = model?.variant
+
         await ctx.client.session.promptAsync({
           path: { id: mainSessionID },
           body: {
             ...(agent ? { agent } : {}),
-            ...(model ? { model } : {}),
+            ...(launchModel ? { model: launchModel } : {}),
+            ...(launchVariant ? { variant: launchVariant } : {}),
             ...(tools ? { tools } : {}),
             parts: [createInternalAgentTextPart(reminder)],
           },