the session readers use getline(3), which a Windows CRT does not have

Building the Windows TUI by hand -- the first local build since the CI file
went away -- stopped in src/tools/session_tools.c: `getline` was an implicit
declaration there, which this GCC treats as an error. src/session.c had a
private fgetc() shim for exactly that; the session-list scan is newer and used
the POSIX call directly, and only the Windows build notices.

The shim moves to os_compat as os_getline(): getline(3) itself on Unix, the
fgetc() loop on Windows, one prototype in the header so a caller reads the same
everywhere. src/session.c drops its copy and calls it; the scan does too (its
`ssize_t` becomes `long long`, which Windows has).

make check is green on Linux, the Windows cross build now finishes and
packages (dist/cst-agent-0.9.7-windows-x86_64.zip plus the NSIS setup), and the
static Linux tarball was rebuilt with it.

src/os_compat.c

@@ -1217,3 +1217,40 @@ int unsetenv(const char *name) {
 }
 
 #endif /* _WIN32 */
+
+/* getline(3) itself where the libc has it; the same thing spelled out with
+ * fgetc() where it does not (Windows), so the callers read the same on every
+ * platform. */
+long long os_getline(char **lineptr, size_t *n, FILE *stream) {
+#ifndef _WIN32
+  return (long long)getline(lineptr, n, stream);
+#else
+  if (!lineptr || !n || !stream)
+    return -1;
+  if (!*lineptr || *n == 0) {
+    *n = 256;
+    *lineptr = (char *)malloc(*n);
+    if (!*lineptr)
+      return -1;
+  }
+  size_t len = 0;
+  int c = 0;
+  while ((c = fgetc(stream)) != EOF) {
+    if (len + 2 > *n) {
+      const size_t nn = (*n) * 2;
+      char *nb = (char *)realloc(*lineptr, nn);
+      if (!nb)
+        return -1;
+      *lineptr = nb;
+      *n = nn;
+    }
+    (*lineptr)[len++] = (char)c;
+    if (c == '\n')
+      break;
+  }
+  if (len == 0 && c == EOF)
+    return -1;
+  (*lineptr)[len] = 0;
+  return (long long)len;
+#endif
+}

src/session.c

@@ -15,39 +15,7 @@
 #include <stdlib.h>
 #include <string.h>
 
-#ifdef _WIN32
-typedef long long cst_ssize_t;
-static cst_ssize_t cst_getline(char **lineptr, size_t *n, FILE *stream) {
-  if (!lineptr || !n || !stream)
-    return -1;
-  if (!*lineptr || *n == 0) {
-    *n = 256;
-    *lineptr = (char *)malloc(*n);
-    if (!*lineptr)
-      return -1;
-  }
-  size_t len = 0;
-  int c = 0;
-  while ((c = fgetc(stream)) != EOF) {
-    if (len + 2 > *n) {
-      size_t nn = (*n) * 2;
-      char *nb = (char *)realloc(*lineptr, nn);
-      if (!nb)
-        return -1;
-      *lineptr = nb;
-      *n = nn;
-    }
-    (*lineptr)[len++] = (char)c;
-    if (c == '\n')
-      break;
-  }
-  if (len == 0 && c == EOF)
-    return -1;
-  (*lineptr)[len] = 0;
-  return (cst_ssize_t)len;
-}
-#define getline cst_getline
-#endif
+#include "os_compat.h"
 
 struct cst_session {
   char path[4096];
@@ -158,7 +126,7 @@ static void load_existing(cst_session_t *s) {
     return;
   char *line = NULL;
   size_t cap = 0;
-  while (getline(&line, &cap, rp) != -1) {
+  while (os_getline(&line, &cap, rp) != -1) {
     cJSON *o = cJSON_Parse(line);
     if (!o || !cJSON_IsObject(o)) {
       cJSON_Delete(o);

src/tools/session_tools.c

@@ -121,8 +121,8 @@ int cst_tool_session_search(const cst_tool_ctx_t *ctx, const ctl_tool_call_t *c,
     char *line = NULL;
     size_t cap = 0;
     cst_buf_t one = {0};
-    ssize_t got;
-    while ((got = getline(&line, &cap, fp)) > 0) {
+    long long got;
+    while ((got = os_getline(&line, &cap, fp)) > 0) {
       lineno++;
       scanned_bytes += got;
       /* A tool output line can be megabytes (a whole file read back): such a