refactor(shared): move parseModelString out of delegate-task to break cross-tool coupling

Move parseModelString into src/shared so callers can depend on a neutral module instead of reaching into delegate-task internals.

Cross-tool coupling violates module boundaries, and this keeps call-omo-agent plus runtime-fallback from importing through a sibling tool.

src/shared/index.ts

@@ -78,3 +78,4 @@ export * from "./plugin-identity"
 export * from "./log-legacy-plugin-startup-warning"
 export * from "./task-system-enabled"
 export * from "./parse-tools-config"
+export { parseModelString } from "./model-string-parser"

src/shared/model-string-parser.ts

@@ -0,0 +1,63 @@
+const KNOWN_VARIANTS = new Set([
+  "low",
+  "medium",
+  "high",
+  "xhigh",
+  "max",
+  "minimal",
+  "none",
+  "auto",
+  "thinking",
+])
+
+export function parseVariantFromModelID(rawModelID: string): { modelID: string; variant?: string } {
+  const trimmedModelID = rawModelID.trim()
+  if (!trimmedModelID) {
+    return { modelID: "" }
+  }
+
+  const parenthesizedVariant = trimmedModelID.match(/^(.*)\(([^()]+)\)\s*$/)
+  if (parenthesizedVariant) {
+    const modelID = parenthesizedVariant[1]?.trim() ?? ""
+    const variant = parenthesizedVariant[2]?.trim()
+    return variant ? { modelID, variant } : { modelID }
+  }
+
+  const spaceVariant = trimmedModelID.match(/^(.*\S)\s+([a-z][a-z0-9_-]*)$/i)
+  if (spaceVariant) {
+    const modelID = spaceVariant[1]?.trim() ?? ""
+    const variant = spaceVariant[2]?.trim().toLowerCase()
+    if (variant && KNOWN_VARIANTS.has(variant)) {
+      return { modelID, variant }
+    }
+  }
+
+  return { modelID: trimmedModelID }
+}
+
+export function parseModelString(
+  model: string,
+): { providerID: string; modelID: string; variant?: string } | undefined {
+  const trimmedModel = model.trim()
+  if (!trimmedModel) return undefined
+
+  const parts = trimmedModel.split("/")
+  if (parts.length < 2) {
+    return undefined
+  }
+
+  const providerID = parts[0]?.trim()
+  const rawModelID = parts.slice(1).join("/").trim()
+  if (!providerID || !rawModelID) {
+    return undefined
+  }
+
+  const parsedModel = parseVariantFromModelID(rawModelID)
+  if (!parsedModel.modelID) {
+    return undefined
+  }
+
+  return parsedModel.variant
+    ? { providerID, modelID: parsedModel.modelID, variant: parsedModel.variant }
+    : { providerID, modelID: parsedModel.modelID }
+}