fix(start-work): restore atlas agent and proper model fallback chain

- Restore agent: 'atlas' in start-work command (removed by PR #1201)
- Fix model-resolver to properly iterate through fallback chain providers
- Remove broken parent model inheritance that bypassed fallback logic
- Add model-suggestion-retry for runtime API failures (cherry-pick 800846c1)

Fixes #1200

src/shared/model-suggestion-retry.ts

@@ -0,0 +1,111 @@
+import type { createOpencodeClient } from "@opencode-ai/sdk"
+import { log } from "./logger"
+
+type Client = ReturnType<typeof createOpencodeClient>
+
+export interface ModelSuggestionInfo {
+  providerID: string
+  modelID: string
+  suggestion: string
+}
+
+function extractMessage(error: unknown): string {
+  if (typeof error === "string") return error
+  if (error instanceof Error) return error.message
+  if (typeof error === "object" && error !== null) {
+    const obj = error as Record<string, unknown>
+    if (typeof obj.message === "string") return obj.message
+    try {
+      return JSON.stringify(error)
+    } catch {
+      return ""
+    }
+  }
+  return String(error)
+}
+
+export function parseModelSuggestion(error: unknown): ModelSuggestionInfo | null {
+  if (!error) return null
+
+  if (typeof error === "object") {
+    const errObj = error as Record<string, unknown>
+
+    if (errObj.name === "ProviderModelNotFoundError" && typeof errObj.data === "object" && errObj.data !== null) {
+      const data = errObj.data as Record<string, unknown>
+      const suggestions = data.suggestions
+      if (Array.isArray(suggestions) && suggestions.length > 0 && typeof suggestions[0] === "string") {
+        return {
+          providerID: String(data.providerID ?? ""),
+          modelID: String(data.modelID ?? ""),
+          suggestion: suggestions[0],
+        }
+      }
+      return null
+    }
+
+    for (const key of ["data", "error", "cause"] as const) {
+      const nested = errObj[key]
+      if (nested && typeof nested === "object") {
+        const result = parseModelSuggestion(nested)
+        if (result) return result
+      }
+    }
+  }
+
+  const message = extractMessage(error)
+  if (!message) return null
+
+  const modelMatch = message.match(/model not found:\s*([^/\s]+)\s*\/\s*([^.\s]+)/i)
+  const suggestionMatch = message.match(/did you mean:\s*([^,?]+)/i)
+
+  if (modelMatch && suggestionMatch) {
+    return {
+      providerID: modelMatch[1].trim(),
+      modelID: modelMatch[2].trim(),
+      suggestion: suggestionMatch[1].trim(),
+    }
+  }
+
+  return null
+}
+
+interface PromptBody {
+  model?: { providerID: string; modelID: string }
+  [key: string]: unknown
+}
+
+interface PromptArgs {
+  path: { id: string }
+  body: PromptBody
+  [key: string]: unknown
+}
+
+export async function promptWithModelSuggestionRetry(
+  client: Client,
+  args: PromptArgs,
+): Promise<void> {
+  try {
+    await client.session.prompt(args as Parameters<typeof client.session.prompt>[0])
+  } catch (error) {
+    const suggestion = parseModelSuggestion(error)
+    if (!suggestion || !args.body.model) {
+      throw error
+    }
+
+    log("[model-suggestion-retry] Model not found, retrying with suggestion", {
+      original: `${suggestion.providerID}/${suggestion.modelID}`,
+      suggested: suggestion.suggestion,
+    })
+
+    await client.session.prompt({
+      ...args,
+      body: {
+        ...args.body,
+        model: {
+          providerID: suggestion.providerID,
+          modelID: suggestion.suggestion,
+        },
+      },
+    } as Parameters<typeof client.session.prompt>[0])
+  }
+}