feat(hooks): add sisyphus-gpt-hephaestus-reminder hook

Shows error toast when Sisyphus runs with a GPT model, nudging user to
use Hephaestus instead.

🤖 Generated with [OhMyOpenCode](https://github.com/code-yeongyu/oh-my-opencode)

src/hooks/index.ts

@@ -27,6 +27,7 @@ export { createInteractiveBashSessionHook } from "./interactive-bash-session";
 export { createThinkingBlockValidatorHook } from "./thinking-block-validator";
 export { createCategorySkillReminderHook } from "./category-skill-reminder";
 export { createRalphLoopHook, type RalphLoopHook } from "./ralph-loop";
+export { createSisyphusGptHephaestusReminderHook } from "./sisyphus-gpt-hephaestus-reminder";
 export { createAutoSlashCommandHook } from "./auto-slash-command";
 export { createEditErrorRecoveryHook } from "./edit-error-recovery";
 export { createJsonErrorRecoveryHook } from "./json-error-recovery";

src/hooks/sisyphus-gpt-hephaestus-reminder/hook.ts

@@ -0,0 +1,37 @@
+import type { PluginInput } from "@opencode-ai/plugin"
+import { getSessionAgent } from "../../features/claude-code-session-state"
+import { log } from "../../shared"
+
+const TOAST_TITLE = "Use Hephaestus for GPT Models"
+const TOAST_MESSAGE = "Sisyphus is using a GPT model. Use Hephaestus and include 'ulw' in your prompt."
+
+export function createSisyphusGptHephaestusReminderHook(ctx: PluginInput) {
+  return {
+    "chat.message": async (input: {
+      sessionID: string
+      agent?: string
+      model?: { providerID: string; modelID: string }
+    }): Promise<void> => {
+      const agentName = (input.agent ?? getSessionAgent(input.sessionID) ?? "").toLowerCase()
+      const modelID = input.model?.modelID?.toLowerCase() ?? ""
+
+      if (agentName !== "sisyphus" || !modelID.includes("gpt")) {
+        return
+      }
+
+      await ctx.client.tui.showToast({
+        body: {
+          title: TOAST_TITLE,
+          message: TOAST_MESSAGE,
+          variant: "error",
+          duration: 5000,
+        },
+      }).catch((error) => {
+        log("[sisyphus-gpt-hephaestus-reminder] Failed to show toast", {
+          sessionID: input.sessionID,
+          error,
+        })
+      })
+    },
+  }
+}

src/hooks/sisyphus-gpt-hephaestus-reminder/index.test.ts

@@ -0,0 +1,78 @@
+import { describe, expect, test, spyOn } from "bun:test"
+import { createSisyphusGptHephaestusReminderHook } from "./index"
+import { _resetForTesting, updateSessionAgent } from "../../features/claude-code-session-state"
+
+describe("sisyphus-gpt-hephaestus-reminder hook", () => {
+  test("shows error toast when sisyphus uses gpt model", async () => {
+    // given - sisyphus agent with gpt model
+    const showToast = spyOn({
+      fn: async () => ({}),
+    }, "fn")
+    const hook = createSisyphusGptHephaestusReminderHook({
+      client: {
+        tui: { showToast },
+      },
+    } as any)
+
+    // when - chat.message runs
+    await hook["chat.message"]?.({
+      sessionID: "ses_1",
+      agent: "sisyphus",
+      model: { providerID: "openai", modelID: "gpt-5.3-codex" },
+    })
+
+    // then - error toast is shown
+    expect(showToast).toHaveBeenCalledTimes(1)
+    expect(showToast.mock.calls[0]?.[0]).toMatchObject({
+      body: {
+        title: "Use Hephaestus for GPT Models",
+        variant: "error",
+      },
+    })
+  })
+
+  test("does not show toast for non-gpt model", async () => {
+    // given - sisyphus agent with non-gpt model
+    const showToast = spyOn({
+      fn: async () => ({}),
+    }, "fn")
+    const hook = createSisyphusGptHephaestusReminderHook({
+      client: {
+        tui: { showToast },
+      },
+    } as any)
+
+    // when - chat.message runs with claude model
+    await hook["chat.message"]?.({
+      sessionID: "ses_2",
+      agent: "sisyphus",
+      model: { providerID: "anthropic", modelID: "claude-opus-4-6" },
+    })
+
+    // then - no toast
+    expect(showToast).toHaveBeenCalledTimes(0)
+  })
+
+  test("uses session agent fallback when input agent is missing", async () => {
+    // given - session agent saved as sisyphus
+    _resetForTesting()
+    updateSessionAgent("ses_3", "sisyphus")
+    const showToast = spyOn({
+      fn: async () => ({}),
+    }, "fn")
+    const hook = createSisyphusGptHephaestusReminderHook({
+      client: {
+        tui: { showToast },
+      },
+    } as any)
+
+    // when - chat.message runs without input.agent
+    await hook["chat.message"]?.({
+      sessionID: "ses_3",
+      model: { providerID: "openai", modelID: "gpt-5.2" },
+    })
+
+    // then - toast shown via fallback agent lookup
+    expect(showToast).toHaveBeenCalledTimes(1)
+  })
+})

src/hooks/sisyphus-gpt-hephaestus-reminder/index.ts

@@ -0,0 +1 @@
+export { createSisyphusGptHephaestusReminderHook } from "./hook"