fix: clamp max-concurrency in custom analysis to avoid deadlock and panic (#1700)

RunCustomAnalysis built its worker semaphore directly from the unvalidated
a.MaxConcurrency field, unlike RunAnalysis which clamps the value first. With
the user-supplied --max-concurrency flag this caused two failures:

- --max-concurrency 0 makes an unbuffered channel, so the pre-send blocks
  waiting for a receiver that is only launched on the next line, deadlocking
  the whole analyze command whenever a custom analyzer is configured.
- --max-concurrency -1 makes make(chan struct{}, -1) panic with
  "makechan: size out of range".

Apply the same lower/upper bound clamp RunAnalysis already uses (default 10 for
non-positive values, cap at 100). Add regression tests covering both cases.

Signed-off-by: Anas Khan <83116240+anxkhn@users.noreply.github.com>
Co-authored-by: Alex Jones <1235925+AlexsJones@users.noreply.github.com>

pkg/analysis/analysis.go

@@ -260,7 +260,16 @@ func (a *Analysis) RunCustomAnalysis() {
 		return
 	}
 
-	semaphore := make(chan struct{}, a.MaxConcurrency)
+	// Set a reasonable maximum for concurrency to prevent excessive memory allocation
+	const maxAllowedConcurrency = 100
+	concurrency := a.MaxConcurrency
+	if concurrency <= 0 {
+		concurrency = 10 // Default value if not set
+	} else if concurrency > maxAllowedConcurrency {
+		concurrency = maxAllowedConcurrency // Cap at a reasonable maximum
+	}
+
+	semaphore := make(chan struct{}, concurrency)
 	var wg sync.WaitGroup
 	var mutex sync.Mutex
 	verbose := viper.GetBool("verbose")

pkg/analysis/analysis_test.go

@@ -20,6 +20,7 @@ import (
 	"reflect"
 	"strings"
 	"testing"
+	"time"
 
 	"github.com/agiledragon/gomonkey/v2"
 	"github.com/k8sgpt-ai/k8sgpt/pkg/ai"
@@ -634,6 +635,48 @@ func TestVerbose_RunCustomAnalysisWithCustomAnalyzer(t *testing.T) {
 	}
 }
 
+// Test: RunCustomAnalysis must not deadlock when MaxConcurrency is 0.
+// A non-positive value previously produced an unbuffered semaphore whose only
+// receiver is launched after the blocking send, hanging the command forever.
+func TestRunCustomAnalysisZeroConcurrency(t *testing.T) {
+	viper.Set("custom_analyzers", []map[string]interface{}{
+		{
+			"name":       "TestCustomAnalyzer",
+			"connection": map[string]interface{}{"url": "127.0.0.1", "port": "2333"},
+		},
+	})
+
+	analysisObj := &Analysis{
+		MaxConcurrency: 0,
+	}
+
+	done := make(chan struct{})
+	go func() {
+		analysisObj.RunCustomAnalysis()
+		close(done)
+	}()
+
+	select {
+	case <-done:
+	case <-time.After(10 * time.Second):
+		t.Fatal("RunCustomAnalysis deadlocked with MaxConcurrency=0")
+	}
+}
+
+// Test: RunCustomAnalysis must not panic when MaxConcurrency is negative.
+// make(chan struct{}, negative) previously panicked with "makechan: size out of range".
+func TestRunCustomAnalysisNegativeConcurrency(t *testing.T) {
+	viper.Set("custom_analyzers", []interface{}{})
+
+	analysisObj := &Analysis{
+		MaxConcurrency: -1,
+	}
+
+	require.NotPanics(t, func() {
+		analysisObj.RunCustomAnalysis()
+	})
+}
+
 // Test: Verbose output in GetAIResults
 func TestVerbose_GetAIResults(t *testing.T) {
 	viper.Set("verbose", true)