fix(mcp): do not end an idle stdio server by closing stdin (#71)

After 30 minutes without a message the idle monitor closed stdin and expected the read loop to end. On a real, blocking stdin a read already in progress is not woken by closing the file, so the server lived on, the client's next message completed that read and the one after failed with 'read /dev/stdin: file already closed', which ended the connection mid-call.

The idle shutdown is now off by default (a stdio server lives as long as its client; orphans are still caught by the parent check). CLAUDE_MNEMONIC_MCP_IDLE_TIMEOUT (a Go duration) turns it on, and then it cancels the loop's context so Run returns nil instead of closing stdin.

Co-authored-by: Claude Sonnet 5.5 <[email protected]>

internal/mcp/idle_env_test.go

@@ -0,0 +1,38 @@
+package mcp
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestIdleTimeoutFromEnv(t *testing.T) {
+	// The idle shutdown is off unless asked for; anything that is not a positive duration leaves it off.
+	for value, want := range map[string]time.Duration{
+		"":     0,
+		"0":    0,
+		"abc":  0,
+		"-5m":  0,
+		"45":   0, // a bare number is not a duration
+		"90m":  90 * time.Minute,
+		"2h":   2 * time.Hour,
+		"30s":  30 * time.Second,
+		" 2h ": 0, // not trimmed: the operator wrote it, so it is wrong rather than guessed
+	} {
+		t.Run(value, func(t *testing.T) {
+			t.Setenv(IdleTimeoutEnv, value)
+			assert.Equal(t, want, idleTimeoutFromEnv())
+		})
+	}
+}
+
+func TestNewServer_HasNoIdleTimeoutByDefault(t *testing.T) {
+	t.Setenv(IdleTimeoutEnv, "")
+	assert.Zero(t, NewServer(nil, "http://localhost:1", "p", "v").idleTimeout)
+}
+
+func TestNewServer_TakesTheIdleTimeoutFromTheEnvironment(t *testing.T) {
+	t.Setenv(IdleTimeoutEnv, "3h")
+	assert.Equal(t, 3*time.Hour, NewServer(nil, "http://localhost:1", "p", "v").idleTimeout)
+}