feat: add Agent SDK support with USE_AGENT_SDK feature flag (#698)

* feat: add Agent SDK support with USE_AGENT_SDK feature flag

Add a feature-flagged code path that uses the Agent SDK instead of
spawning the CLI as a subprocess. When USE_AGENT_SDK=true is set,
the new SDK path is used; otherwise, existing CLI behavior is unchanged.

Changes:
- Add parse-sdk-options.ts for parsing ClaudeOptions into SDK format
- Add run-claude-sdk.ts for SDK execution with query() function
- Update run-claude.ts with feature flag check at entry point
- Update update-comment-link.ts to handle both cost_usd and total_cost_usd
- Add @anthropic-ai/claude-agent-sdk dependency

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

* refactor: simplify SDK types by using @anthropic-ai/claude-agent-sdk types directly

- Remove duplicate SdkRunOptions and McpStdioServerConfig types
- Use SDK's Options and McpStdioServerConfig types directly
- Return { sdkOptions, showFullOutput, hasJsonSchema } from parseSdkOptions
- Remove unnecessary convertMcpServers function
- Net reduction of ~70 lines

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

* refactor: use extraArgs for claudeArgs pass-through to CLI

Simplify option parsing by converting claudeArgs to extraArgs record
and letting the SDK/CLI handle --mcp-config, --json-schema, etc.

- Remove extractJsonSchema and parseMcpConfigs functions
- Add parseClaudeArgsToExtraArgs for simple flag parsing
- CLI handles complex args like --mcp-config directly

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

* ci

* refactor: remove hardcoded permission bypass flags

The SDK path should match CLI path behavior - permissions are handled
by the CLI itself, not hardcoded in the action.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

* chore: add logging for SDK vs CLI path selection

---------

Co-authored-by: Claude <noreply@anthropic.com>

base-action/src/run-claude.ts

@@ -5,6 +5,8 @@ import { unlink, writeFile, stat, readFile } from "fs/promises";
 import { createWriteStream } from "fs";
 import { spawn } from "child_process";
 import { parse as parseShellArgs } from "shell-quote";
+import { runClaudeWithSdk } from "./run-claude-sdk";
+import { parseSdkOptions } from "./parse-sdk-options";
 
 const execAsync = promisify(exec);
 
@@ -165,6 +167,17 @@ export async function parseAndSetStructuredOutputs(
 }
 
 export async function runClaude(promptPath: string, options: ClaudeOptions) {
+  // Feature flag: use SDK path when USE_AGENT_SDK=true
+  const useAgentSdk = process.env.USE_AGENT_SDK === "true";
+  console.log(
+    `Using ${useAgentSdk ? "Agent SDK" : "CLI"} path (USE_AGENT_SDK=${process.env.USE_AGENT_SDK ?? "unset"})`,
+  );
+
+  if (useAgentSdk) {
+    const parsedOptions = parseSdkOptions(options);
+    return runClaudeWithSdk(promptPath, parsedOptions);
+  }
+
   const config = prepareRunConfig(promptPath, options);
 
   // Detect if --json-schema is present in claude args