fix(mcp): address QA round 2 findings

- Add explicit fallback path when fcntl(F_GETFL) fails: skip the FILE*
  peek and fall through directly to blocking poll so idle eviction still
  fires on timeout (Finding 1)
- Strengthen C unit test: verify id:1 (initialize) and id:2 (tools/list)
  response IDs are both present, not just a substring match on "tools"
  (Finding 2)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: shanemccarron-maker

src/mcp/mcp.c

@@ -2425,20 +2425,10 @@ int cbm_mcp_server_run(cbm_mcp_server_t *srv, FILE *in, FILE *out) {
              * would block indefinitely, preventing the Phase 3 idle eviction
              * timeout from ever firing. */
             int saved_flags = fcntl(fd, F_GETFL);
-            if (saved_flags >= 0) {
-                (void)fcntl(fd, F_SETFL, saved_flags | O_NONBLOCK);
-            }
-            int c = fgetc(in);
-            if (saved_flags >= 0) {
-                (void)fcntl(fd, F_SETFL, saved_flags); /* restore blocking */
-            }
-            if (c == EOF) {
-                if (feof(in)) {
-                    break; /* true EOF */
-                }
-                /* No buffered data (EAGAIN from non-blocking read) — clear the
-                 * ferror indicator set by EAGAIN, then do the blocking poll. */
-                clearerr(in);
+            if (saved_flags < 0) {
+                /* fcntl failed (should not happen on a valid fd) — skip the
+                 * FILE* peek and fall straight through to the blocking poll so
+                 * idle eviction still fires on timeout. */
                 pr = poll(&pfd, 1, STORE_IDLE_TIMEOUT_S * 1000);
                 if (pr < 0) {
                     break;
@@ -2448,8 +2438,28 @@ int cbm_mcp_server_run(cbm_mcp_server_t *srv, FILE *in, FILE *out) {
                     continue;
                 }
             } else {
-                /* Buffered data found — push back and fall through to getline */
-                (void)ungetc(c, in);
+                (void)fcntl(fd, F_SETFL, saved_flags | O_NONBLOCK);
+                int c = fgetc(in);
+                (void)fcntl(fd, F_SETFL, saved_flags); /* restore blocking */
+                if (c == EOF) {
+                    if (feof(in)) {
+                        break; /* true EOF */
+                    }
+                    /* No buffered data (EAGAIN from non-blocking read) — clear
+                     * the ferror indicator set by EAGAIN, then blocking poll. */
+                    clearerr(in);
+                    pr = poll(&pfd, 1, STORE_IDLE_TIMEOUT_S * 1000);
+                    if (pr < 0) {
+                        break;
+                    }
+                    if (pr == 0) {
+                        cbm_mcp_server_evict_idle(srv, STORE_IDLE_TIMEOUT_S);
+                        continue;
+                    }
+                } else {
+                    /* Buffered data found — push back and fall through to getline */
+                    (void)ungetc(c, in);
+                }
             }
         }
 #endif

tests/test_mcp.c

@@ -1272,11 +1272,16 @@ TEST(mcp_server_run_rapid_messages) {
 
     ASSERT_EQ(rc, 0);
 
-    /* Verify that tools/list response is present in output */
+    /* Verify both responses are present:
+     *   id:1 — initialize response
+     *   id:2 — tools/list response (notifications/initialized produces none)
+     * and that the tools list payload is included. */
     rewind(out_fp);
     char buf[4096] = {0};
     size_t nread = fread(buf, 1, sizeof(buf) - 1, out_fp);
     ASSERT_TRUE(nread > 0);
+    ASSERT_NOT_NULL(strstr(buf, "\"id\":1"));
+    ASSERT_NOT_NULL(strstr(buf, "\"id\":2"));
     ASSERT_NOT_NULL(strstr(buf, "tools"));
 
     cbm_mcp_server_free(srv);