fix(ccw): only cache positive tool availability results

Fixes CLI tool detection failure after server restart.

The previous caching implementation cached negative results (errors,
timeouts) which caused persistent failures if the first check failed
for any transient reason (environment, timing, etc.).

Changes:
- Only cache positive tool availability results
- Don't cache errors or timeouts - they may be transient
- Subsequent checks will retry if a tool wasn't found

This ensures that once a tool is found, lookups are fast, but
transient failures don't persist in the cache.

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

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

ccw/src/tools/cli-executor.ts

@@ -222,39 +222,27 @@ async function checkToolAvailability(tool: string): Promise<ToolAvailability> {
         ? { available: true, path: stdout.trim().split('\n')[0] }
         : { available: false, path: null };
 
-      // Cache the result
-      toolAvailabilityCache.set(tool, {
-        result,
-        timestamp: Date.now()
-      });
+      // Only cache positive results to avoid caching transient failures
+      if (result.available) {
+        toolAvailabilityCache.set(tool, {
+          result,
+          timestamp: Date.now()
+        });
+      }
 
       resolve(result);
     });
 
     child.on('error', () => {
-      const result: ToolAvailability = { available: false, path: null };
-
-      // Cache negative results too
-      toolAvailabilityCache.set(tool, {
-        result,
-        timestamp: Date.now()
-      });
-
-      resolve(result);
+      // Don't cache errors - they may be transient
+      resolve({ available: false, path: null });
     });
 
     // Timeout after 5 seconds
     setTimeout(() => {
       child.kill();
-      const result: ToolAvailability = { available: false, path: null };
-
-      // Cache timeout results
-      toolAvailabilityCache.set(tool, {
-        result,
-        timestamp: Date.now()
-      });
-
-      resolve(result);
+      // Don't cache timeouts - they may be transient
+      resolve({ available: false, path: null });
     }, 5000);
   });
 }