fix(provider-cache): extract models from provider.list().all response

OpenCode SDK does not expose client.model.list API. This caused the
provider-models cache to always be empty (models: {}), which in turn
caused delegate-task categories with requiresModel (e.g., 'deep',
'artistry') to fail with misleading 'Unknown category' errors.

Changes:
- connected-providers-cache.ts: Extract models from provider.list()
  response's .all array instead of calling non-existent client.model.list
- category-resolver.ts: Distinguish between 'unknown category' and
  'model not available' errors with clearer error messages
- Add comprehensive tests for both fixes

Bug chain:
client.model?.list is undefined -> empty cache -> isModelAvailable
returns false for requiresModel categories -> null returned from
resolveCategoryConfig -> 'Unknown category' error (wrong message)

src/tools/delegate-task/category-resolver.test.ts

@@ -0,0 +1,62 @@
+import { describe, test, expect } from "bun:test"
+import { resolveCategoryExecution } from "./category-resolver"
+import type { ExecutorContext } from "./executor-types"
+
+describe("resolveCategoryExecution", () => {
+	const createMockExecutorContext = (): ExecutorContext => ({
+		client: {} as any,
+		manager: {} as any,
+		directory: "/tmp/test",
+		userCategories: {},
+		sisyphusJuniorModel: undefined,
+	})
+
+	test("returns clear error when category exists but required model is not available", async () => {
+		//#given
+		const args = {
+			category: "deep",
+			prompt: "test prompt",
+			description: "Test task",
+			run_in_background: false,
+			load_skills: [],
+			blockedBy: undefined,
+			enableSkillTools: false,
+		}
+		const executorCtx = createMockExecutorContext()
+		const inheritedModel = undefined
+		const systemDefaultModel = "anthropic/claude-sonnet-4-5"
+
+		//#when
+		const result = await resolveCategoryExecution(args, executorCtx, inheritedModel, systemDefaultModel)
+
+		//#then
+		expect(result.error).toBeDefined()
+		expect(result.error).toContain("deep")
+		expect(result.error).toMatch(/model.*not.*available|requires.*model/i)
+		expect(result.error).not.toContain("Unknown category")
+	})
+
+	test("returns 'unknown category' error for truly unknown categories", async () => {
+		//#given
+		const args = {
+			category: "definitely-not-a-real-category-xyz123",
+			prompt: "test prompt",
+			description: "Test task",
+			run_in_background: false,
+			load_skills: [],
+			blockedBy: undefined,
+			enableSkillTools: false,
+		}
+		const executorCtx = createMockExecutorContext()
+		const inheritedModel = undefined
+		const systemDefaultModel = "anthropic/claude-sonnet-4-5"
+
+		//#when
+		const result = await resolveCategoryExecution(args, executorCtx, inheritedModel, systemDefaultModel)
+
+		//#then
+		expect(result.error).toBeDefined()
+		expect(result.error).toContain("Unknown category")
+		expect(result.error).toContain("definitely-not-a-real-category-xyz123")
+	})
+})