fix: model format normalization and explicit config cache bypass

- Add normalizeModelFormat() utility for string/object model handling
- Update subagent-resolver to handle both model formats
- Add explicitUserConfig flag to ModelResolutionResult
- Set explicitUserConfig: true when user model is found in pipeline

This fixes the issue where plugin-provided models fail cache validation
and fall through to random fallback models.

src/shared/model-format-normalizer.test.ts

@@ -0,0 +1,46 @@
+import { describe, it, expect } from "bun:test"
+import { normalizeModelFormat } from "./model-format-normalizer"
+
+describe("normalizeModelFormat", () => {
+  describe("string format input", () => {
+    it("splits provider/model format correctly", () => {
+      const result = normalizeModelFormat("opencode/glm-5-free")
+      expect(result).toEqual({ providerID: "opencode", modelID: "glm-5-free" })
+    })
+
+    it("handles provider with multiple slashes", () => {
+      const result = normalizeModelFormat("anthropic/claude-opus-4-6/max")
+      expect(result).toEqual({ providerID: "anthropic", modelID: "claude-opus-4-6/max" })
+    })
+
+    it("returns undefined for malformed string without separator", () => {
+      const result = normalizeModelFormat("invalid")
+      expect(result).toBeUndefined()
+    })
+
+    it("returns undefined for empty string", () => {
+      const result = normalizeModelFormat("")
+      expect(result).toBeUndefined()
+    })
+  })
+
+  describe("object format input", () => {
+    it("passthroughs object format unchanged", () => {
+      const input = { providerID: "opencode", modelID: "glm-5-free" }
+      const result = normalizeModelFormat(input)
+      expect(result).toEqual(input)
+    })
+  })
+
+  describe("edge cases", () => {
+    it("returns undefined for null", () => {
+      const result = normalizeModelFormat(null)
+      expect(result).toBeUndefined()
+    })
+
+    it("returns undefined for undefined", () => {
+      const result = normalizeModelFormat(undefined)
+      expect(result).toBeUndefined()
+    })
+  })
+})

src/shared/model-format-normalizer.ts

@@ -0,0 +1,20 @@
+export function normalizeModelFormat(
+  model: string | { providerID: string; modelID: string }
+): { providerID: string; modelID: string } | undefined {
+  if (!model) {
+    return undefined
+  }
+
+  if (typeof model === "object" && "providerID" in model && "modelID" in model) {
+    return { providerID: model.providerID, modelID: model.modelID }
+  }
+
+  if (typeof model === "string") {
+    const parts = model.split("/")
+    if (parts.length >= 2) {
+      return { providerID: parts[0], modelID: parts.slice(1).join("/") }
+    }
+  }
+
+  return undefined
+}

src/shared/model-resolution-pipeline.ts

@@ -33,6 +33,7 @@ export type ModelResolutionResult = {
   variant?: string
   attempted?: string[]
   reason?: string
+  explicitUserConfig?: boolean
 }
 
 function normalizeModel(model?: string): string | undefined {
@@ -58,7 +59,7 @@ export function resolveModelPipeline(
   const normalizedUserModel = normalizeModel(intent?.userModel)
   if (normalizedUserModel) {
     log("Model resolved via config override", { model: normalizedUserModel })
-    return { model: normalizedUserModel, provenance: "override" }
+    return { model: normalizedUserModel, provenance: "override", explicitUserConfig: true }
   }
 
   const normalizedCategoryDefault = normalizeModel(intent?.categoryDefaultModel)

src/tools/delegate-task/subagent-resolver.ts

@@ -2,7 +2,7 @@ import type { DelegateTaskArgs } from "./types"
 import type { ExecutorContext } from "./executor-types"
 import { isPlanFamily } from "./constants"
 import { SISYPHUS_JUNIOR_AGENT } from "./sisyphus-junior-agent"
-import { parseModelString } from "./model-string-parser"
+import { normalizeModelFormat } from "../../shared/model-format-normalizer"
 import { AGENT_MODEL_REQUIREMENTS } from "../../shared/model-requirements"
 import { getAgentDisplayName, getAgentConfigKey } from "../../shared/agent-display-names"
 import { normalizeSDKResponse } from "../../shared"
@@ -99,8 +99,9 @@ Create the work plan directly - that's your job as the planning agent.`,
     if (agentOverride?.model || agentRequirement || matchedAgent.model) {
       const availableModels = await getAvailableModelsForDelegateTask(client)
 
-      const matchedAgentModelStr = matchedAgent.model
-        ? `${matchedAgent.model.providerID}/${matchedAgent.model.modelID}`
+      const normalizedMatchedModel = normalizeModelFormat(matchedAgent.model as Parameters<typeof normalizeModelFormat>[0])
+      const matchedAgentModelStr = normalizedMatchedModel
+        ? `${normalizedMatchedModel.providerID}/${normalizedMatchedModel.modelID}`
         : undefined
 
       const resolution = resolveModelForDelegateTask({
@@ -112,10 +113,10 @@ Create the work plan directly - that's your job as the planning agent.`,
       })
 
       if (resolution) {
-        const parsed = parseModelString(resolution.model)
-        if (parsed) {
+        const normalized = normalizeModelFormat(resolution.model)
+        if (normalized) {
           const variantToUse = agentOverride?.variant ?? resolution.variant
-          categoryModel = variantToUse ? { ...parsed, variant: variantToUse } : parsed
+          categoryModel = variantToUse ? { ...normalized, variant: variantToUse } : normalized
         }
       }
     }