feat(v2): auto-detect Claude CLI path and pass to SDK via pathToClaudeCodeExecutable

Both sidecar runners (agent-runner.ts and agent-runner-deno.ts) now include
findClaudeCli() which checks common paths (~/.local/bin/claude,
~/.claude/local/claude, /usr/local/bin/claude, /usr/bin/claude) and falls
back to `which claude`. The resolved path is passed to the SDK query()
options as pathToClaudeCodeExecutable. If the CLI is not found, an
agent_error is emitted immediately instead of a cryptic SDK failure.

v2/sidecar/agent-runner-deno.ts

@@ -71,10 +71,16 @@ async function handleQuery(msg: QueryMessage) {
     }
   }
 
+  if (!claudePath) {
+    send({ type: "agent_error", sessionId, message: "Claude CLI not found. Install Claude Code first." });
+    return;
+  }
+
   try {
     const q = query({
       prompt,
       options: {
+        pathToClaudeCodeExecutable: claudePath,
         abortController: controller,
         cwd: cwd || Deno.cwd(),
         env: cleanEnv,
@@ -144,6 +150,32 @@ function handleStop(msg: StopMessage) {
   controller.abort();
 }
 
+function findClaudeCli(): string | undefined {
+  const home = Deno.env.get("HOME") ?? Deno.env.get("USERPROFILE") ?? "";
+  const candidates = [
+    `${home}/.local/bin/claude`,
+    `${home}/.claude/local/claude`,
+    "/usr/local/bin/claude",
+    "/usr/bin/claude",
+  ];
+  for (const p of candidates) {
+    try { Deno.statSync(p); return p; } catch { /* not found */ }
+  }
+  try {
+    const proc = new Deno.Command("which", { args: ["claude"], stdout: "piped", stderr: "null" });
+    const out = new TextDecoder().decode(proc.outputSync().stdout).trim();
+    if (out) return out.split("\n")[0];
+  } catch { /* not found */ }
+  return undefined;
+}
+
+const claudePath = findClaudeCli();
+if (claudePath) {
+  log(`Found Claude CLI at ${claudePath}`);
+} else {
+  log("WARNING: Claude CLI not found — agent sessions will fail");
+}
+
 // Main: read NDJSON from stdin
 log("Sidecar started (Deno)");
 send({ type: "ready" });

v2/sidecar/agent-runner.ts

@@ -4,6 +4,10 @@
 
 import { stdin, stdout, stderr } from 'process';
 import { createInterface } from 'readline';
+import { execSync } from 'child_process';
+import { existsSync } from 'fs';
+import { join } from 'path';
+import { homedir } from 'os';
 import { query, type Query } from '@anthropic-ai/claude-agent-sdk';
 
 const rl = createInterface({ input: stdin });
@@ -81,9 +85,15 @@ async function handleQuery(msg: QueryMessage) {
   }
 
   try {
+    if (!claudePath) {
+      send({ type: 'agent_error', sessionId, message: 'Claude CLI not found. Install Claude Code first.' });
+      return;
+    }
+
     const q = query({
       prompt,
       options: {
+        pathToClaudeCodeExecutable: claudePath,
         abortController: controller,
         cwd: cwd || process.cwd(),
         env: cleanEnv,
@@ -155,5 +165,31 @@ function handleStop(msg: StopMessage) {
   session.controller.abort();
 }
 
+function findClaudeCli(): string | undefined {
+  // Check common locations
+  const candidates = [
+    join(homedir(), '.local', 'bin', 'claude'),
+    join(homedir(), '.claude', 'local', 'claude'),
+    '/usr/local/bin/claude',
+    '/usr/bin/claude',
+  ];
+  for (const p of candidates) {
+    if (existsSync(p)) return p;
+  }
+  // Fall back to which/where
+  try {
+    return execSync('which claude 2>/dev/null || where claude 2>nul', { encoding: 'utf-8' }).trim().split('\n')[0];
+  } catch {
+    return undefined;
+  }
+}
+
+const claudePath = findClaudeCli();
+if (claudePath) {
+  log(`Found Claude CLI at ${claudePath}`);
+} else {
+  log('WARNING: Claude CLI not found — agent sessions will fail');
+}
+
 log('Sidecar started');
 send({ type: 'ready' });