refactor: simplify mode system by removing Mode interface and registry (#899)

Replace the over-engineered Mode interface/registry/detector pattern with
straightforward inline logic. There are only 2 modes (tag and agent) and
the complexity wasn't justified.

- Delete Mode interface, registry, and prepare pass-through modules
- Export prepareTagMode() and prepareAgentMode() as standalone functions
- Inline trigger checking and mode dispatch in run.ts/prepare.ts
- Change generatePrompt/createPrompt to take modeName string instead of Mode
- Remove dead code (extractGitHubContext, unused detector helpers)
- Update CLAUDE.md to reflect new architecture

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}`);