refactor: simplify mode system by removing Mode interface and registry

CLAUDE.md

@@ -11,7 +11,7 @@ bun run format:check    # Check formatting
 
 ## What This Is
 
-A GitHub Action that lets Claude respond to `@claude` mentions on issues/PRs (tag mode) or run tasks via `prompt` input (agent mode). Mode is auto-detected: if `prompt` is provided, it's agent mode; if triggered by a comment/issue event with `@claude`, it's tag mode. See `src/modes/registry.ts`.
+A GitHub Action that lets Claude respond to `@claude` mentions on issues/PRs (tag mode) or run tasks via `prompt` input (agent mode). Mode is auto-detected: if `prompt` is provided, it's agent mode; if triggered by a comment/issue event with `@claude`, it's tag mode. See `src/modes/detector.ts`.
 
 ## How It Runs
 
@@ -23,9 +23,9 @@ Single entrypoint: `src/entrypoints/run.ts` orchestrates everything — prepare
 
 **Auth priority**: `github_token` input (user-provided) > GitHub App OIDC token (default). The `claude_code_oauth_token` and `anthropic_api_key` are for the Claude API, not GitHub. Token setup lives in `src/github/token.ts`.
 
-**Mode lifecycle**: Modes implement `shouldTrigger()` → `prepare()` → `prepareContext()` → `getSystemPrompt()`. The registry in `src/modes/registry.ts` picks the mode based on event type and inputs. To add a new mode, implement the `Mode` type from `src/modes/types.ts` and register it.
+**Mode lifecycle**: `detectMode()` in `src/modes/detector.ts` picks the mode name ("tag" or "agent"). Trigger checking and prepare dispatch are inlined in `run.ts`: tag mode calls `prepareTagMode()` from `src/modes/tag/`, agent mode calls `prepareAgentMode()` from `src/modes/agent/`.
 
-**Prompt construction**: `src/prepare/` builds the prompt by fetching GitHub data (`src/github/data/fetcher.ts`), formatting it as markdown (`src/github/data/formatter.ts`), and writing it to a temp file. The prompt includes issue/PR body, comments, diff, and CI status. This is the most important part of the action — it's what Claude sees.
+**Prompt construction**: Tag mode's `prepareTagMode()` builds the prompt by fetching GitHub data (`src/github/data/fetcher.ts`), formatting it as markdown (`src/github/data/formatter.ts`), and writing it to a temp file via `createPrompt()`. Agent mode writes the user's prompt directly. The prompt includes issue/PR body, comments, diff, and CI status. This is the most important part of the action — it's what Claude sees.
 
 ## Things That Will Bite You
 

src/create-prompt/index.ts

@@ -20,7 +20,6 @@ import {
 import type { ParsedGitHubContext } from "../github/context";
 import type { CommonFields, PreparedContext, EventData } from "./types";
 import { GITHUB_SERVER_URL } from "../github/api/config";
-import type { Mode, ModeContext } from "../modes/types";
 import { extractUserRequest } from "../utils/extract-user-request";
 export type { CommonFields, PreparedContext } from "./types";
 
@@ -458,9 +457,31 @@ export function generatePrompt(
   context: PreparedContext,
   githubData: FetchDataResult,
   useCommitSigning: boolean,
-  mode: Mode,
+  modeName: "tag" | "agent",
 ): string {
-  return mode.generatePrompt(context, githubData, useCommitSigning);
+  if (modeName === "agent") {
+    return context.prompt || `Repository: ${context.repository}`;
+  }
+
+  // Tag mode
+  const defaultPrompt = generateDefaultPrompt(
+    context,
+    githubData,
+    useCommitSigning,
+  );
+
+  if (context.githubContext?.inputs?.prompt) {
+    return (
+      defaultPrompt +
+      `
+
+<custom_instructions>
+${context.githubContext.inputs.prompt}
+</custom_instructions>`
+    );
+  }
+
+  return defaultPrompt;
 }
 
 /**
@@ -901,28 +922,20 @@ function extractUserRequestFromContext(
 }
 
 export async function createPrompt(
-  mode: Mode,
-  modeContext: ModeContext,
+  commentId: number,
+  baseBranch: string | undefined,
+  claudeBranch: string | undefined,
   githubData: FetchDataResult,
   context: ParsedGitHubContext,
 ) {
   try {
-    // Prepare the context for prompt generation
-    let claudeCommentId: string = "";
-    if (mode.name === "tag") {
-      if (!modeContext.commentId) {
-        throw new Error(
-          `${mode.name} mode requires a comment ID for prompt generation`,
-        );
-      }
-      claudeCommentId = modeContext.commentId.toString();
-    }
+    const claudeCommentId = commentId.toString();
 
     const preparedContext = prepareContext(
       context,
       claudeCommentId,
-      modeContext.baseBranch,
-      modeContext.claudeBranch,
+      baseBranch,
+      claudeBranch,
     );
 
     await mkdir(`${process.env.RUNNER_TEMP || "/tmp"}/claude-prompts`, {
@@ -934,7 +947,7 @@ export async function createPrompt(
       preparedContext,
       githubData,
       context.inputs.useCommitSigning,
-      mode,
+      "tag",
     );
 
     // Log the final prompt to console
@@ -967,19 +980,12 @@ export async function createPrompt(
     // Set allowed tools
     const hasActionsReadPermission = false;
 
-    // Get mode-specific tools
-    const modeAllowedTools = mode.getAllowedTools();
-    const modeDisallowedTools = mode.getDisallowedTools();
-
     const allAllowedTools = buildAllowedToolsString(
-      modeAllowedTools,
+      [],
       hasActionsReadPermission,
       context.inputs.useCommitSigning,
     );
-    const allDisallowedTools = buildDisallowedToolsString(
-      modeDisallowedTools,
-      modeAllowedTools,
-    );
+    const allDisallowedTools = buildDisallowedToolsString([], []);
 
     core.exportVariable("ALLOWED_TOOLS", allAllowedTools);
     core.exportVariable("DISALLOWED_TOOLS", allDisallowedTools);

src/entrypoints/prepare.ts

@@ -10,8 +10,10 @@ import { setupGitHubToken } from "../github/token";
 import { checkWritePermissions } from "../github/validation/permissions";
 import { createOctokit } from "../github/api/client";
 import { parseGitHubContext, isEntityContext } from "../github/context";
-import { getMode } from "../modes/registry";
-import { prepare } from "../prepare";
+import { detectMode } from "../modes/detector";
+import { prepareTagMode } from "../modes/tag";
+import { prepareAgentMode } from "../modes/agent";
+import { checkContainsTrigger } from "../github/validation/trigger";
 import { collectActionInputsPresence } from "./collect-inputs";
 
 async function run() {
@@ -22,7 +24,10 @@ async function run() {
     const context = parseGitHubContext();
 
     // Auto-detect mode based on context
-    const mode = getMode(context);
+    const modeName = detectMode(context);
+    console.log(
+      `Auto-detected mode: ${modeName} for event: ${context.eventName}`,
+    );
 
     // Setup GitHub token
     const githubToken = await setupGitHubToken();
@@ -46,10 +51,13 @@ async function run() {
     }
 
     // Check trigger conditions
-    const containsTrigger = mode.shouldTrigger(context);
+    const containsTrigger =
+      modeName === "tag"
+        ? isEntityContext(context) && checkContainsTrigger(context)
+        : !!context.inputs?.prompt;
 
     // Debug logging
-    console.log(`Mode: ${mode.name}`);
+    console.log(`Mode: ${modeName}`);
     console.log(`Context prompt: ${context.inputs?.prompt || "NO PROMPT"}`);
     console.log(`Trigger result: ${containsTrigger}`);
 
@@ -63,31 +71,20 @@ async function run() {
       return;
     }
 
-    // Step 5: Use the new modular prepare function
-    const result = await prepare({
-      context,
-      octokit,
-      mode,
-      githubToken,
-    });
+    // Run prepare
+    console.log(
+      `Preparing with mode: ${modeName} for event: ${context.eventName}`,
+    );
+    if (modeName === "tag") {
+      await prepareTagMode({ context, octokit, githubToken });
+    } else {
+      await prepareAgentMode({ context, octokit, githubToken });
+    }
 
     // MCP config is handled by individual modes (tag/agent) and included in their claude_args output
 
     // Expose the GitHub token (Claude App token) as an output
     core.setOutput("github_token", githubToken);
-
-    // Step 6: Get system prompt from mode if available
-    if (mode.getSystemPrompt) {
-      const modeContext = mode.prepareContext(context, {
-        commentId: result.commentId,
-        baseBranch: result.branchInfo.baseBranch,
-        claudeBranch: result.branchInfo.claudeBranch,
-      });
-      const systemPrompt = mode.getSystemPrompt(modeContext);
-      if (systemPrompt) {
-        core.exportVariable("APPEND_SYSTEM_PROMPT", systemPrompt);
-      }
-    }
   } catch (error) {
     const errorMessage = error instanceof Error ? error.message : String(error);
     core.setFailed(`Prepare step failed with error: ${errorMessage}`);

src/entrypoints/run.ts

@@ -17,8 +17,10 @@ import { createOctokit } from "../github/api/client";
 import type { Octokits } from "../github/api/client";
 import { parseGitHubContext, isEntityContext } from "../github/context";
 import type { GitHubContext } from "../github/context";
-import { getMode } from "../modes/registry";
-import { prepare } from "../prepare";
+import { detectMode } from "../modes/detector";
+import { prepareTagMode } from "../modes/tag";
+import { prepareAgentMode } from "../modes/agent";
+import { checkContainsTrigger } from "../github/validation/trigger";
 import { collectActionInputsPresence } from "./collect-inputs";
 import { updateCommentLink } from "./update-comment-link";
 import { formatTurnsFromData } from "./format-turns";
@@ -138,7 +140,10 @@ async function run() {
     // Phase 1: Prepare
     const actionInputsPresent = collectActionInputsPresence();
     context = parseGitHubContext();
-    const mode = getMode(context);
+    const modeName = detectMode(context);
+    console.log(
+      `Auto-detected mode: ${modeName} for event: ${context.eventName}`,
+    );
 
     try {
       githubToken = await setupGitHubToken();
@@ -173,8 +178,11 @@ async function run() {
     }
 
     // Check trigger conditions
-    const containsTrigger = mode.shouldTrigger(context);
-    console.log(`Mode: ${mode.name}`);
+    const containsTrigger =
+      modeName === "tag"
+        ? isEntityContext(context) && checkContainsTrigger(context)
+        : !!context.inputs?.prompt;
+    console.log(`Mode: ${modeName}`);
     console.log(`Context prompt: ${context.inputs?.prompt || "NO PROMPT"}`);
     console.log(`Trigger result: ${containsTrigger}`);
 
@@ -185,31 +193,19 @@ async function run() {
     }
 
     // Run prepare
-    const prepareResult = await prepare({
-      context,
-      octokit,
-      mode,
-      githubToken,
-    });
+    console.log(
+      `Preparing with mode: ${modeName} for event: ${context.eventName}`,
+    );
+    const prepareResult =
+      modeName === "tag"
+        ? await prepareTagMode({ context, octokit, githubToken })
+        : await prepareAgentMode({ context, octokit, githubToken });
 
     commentId = prepareResult.commentId;
     claudeBranch = prepareResult.branchInfo.claudeBranch;
     baseBranch = prepareResult.branchInfo.baseBranch;
     prepareCompleted = true;
 
-    // Set system prompt if available
-    if (mode.getSystemPrompt) {
-      const modeContext = mode.prepareContext(context, {
-        commentId: prepareResult.commentId,
-        baseBranch: prepareResult.branchInfo.baseBranch,
-        claudeBranch: prepareResult.branchInfo.claudeBranch,
-      });
-      const systemPrompt = mode.getSystemPrompt(modeContext);
-      if (systemPrompt) {
-        core.exportVariable("APPEND_SYSTEM_PROMPT", systemPrompt);
-      }
-    }
-
     // Phase 2: Install Claude Code CLI
     await installClaudeCode();