fix(cli): only name an installer that is actually there

`update` hands off to install.sh (install.ps1 on Windows) and prints the command
to run. It built that command from cbm_detect_self_path - the BINARY's directory
- and treated "I resolved my own location" as "the installer is beside me".

Those are different questions. install.sh is placed beside the binary by
install.sh itself, but a binary that was moved, packaged by a distro, or built
from source has no installer next to it. We printed the path anyway:

    bash "/home/<user>/.local/bin/install.sh"
    /usr/bin/bash: /home/<user>/.local/bin/install.sh: No such file or directory

Reported on discussion #1560 (#1632) by a user who was already three releases
deep in install trouble and had just been told, by us, to run a file that does
not exist.

`update` exists to tell someone how to proceed. Ending the interaction on a
command that cannot run is the one outcome it must not produce - and the
fallback text was already there and already correct, naming install.sh as
shipping in the release archive without asserting a path.

The probe goes through cbm_path_info_utf8 so a non-ASCII install directory
resolves on Windows, and rejects a DIRECTORY of that name, because `bash <dir>`
is not a command either. A symlink still counts: it is reported rather than
followed, and the shell runs it perfectly well.

The Windows branch gets the same treatment; it had the identical assumption
about install.ps1.

Reproduce-first and revert-checked: with the probe forced to return true - the
old behaviour - the new test fails with "a directory with no installer must not
be named as one", and passes once it is restored. cli: 276 passed.

Signed-off-by: Martin Vogel <martin.vogel.tech@gmail.com>

src/cli/cli.c

@@ -11972,6 +11972,36 @@ static bool check_already_latest(void) {
 
 #endif /* CBM_CLI_ENABLE_TEST_API */
 
+/* Is the installer script actually present beside the binary? (#1632)
+ *
+ * `update` hands off to install.sh / install.ps1 and prints the command to run.
+ * It derived that path from the binary's own location, which is not the same
+ * question: the installer is placed beside the binary by install.sh, but a
+ * binary moved, packaged, or built from source has no installer next to it, and
+ * we still printed the path. The user's session then ended on a command that
+ * cannot run.
+ *
+ * Checked with cbm_path_info_utf8 so a non-ASCII install path resolves on
+ * Windows. A symlink counts: it is reported rather than followed, and the shell
+ * will run it perfectly well. */
+bool cbm_cli_installer_beside_binary(const char *dir) {
+    if (!dir || !dir[0]) {
+        return false;
+    }
+    char script[CLI_BUF_1K];
+#ifdef _WIN32
+    const char *name = "install.ps1";
+#else
+    const char *name = "install.sh";
+#endif
+    int written = snprintf(script, sizeof(script), "%s/%s", dir, name);
+    if (written <= 0 || (size_t)written >= sizeof(script)) {
+        return false;
+    }
+    cbm_path_info_t info;
+    return cbm_path_info_utf8(script, &info) == 0 && !info.is_directory;
+}
+
 int cbm_cmd_update(int argc, char **argv) {
     parse_auto_answer(argc, argv);
 

src/cli/cli.h

@@ -482,6 +482,12 @@ int cbm_cmd_uninstall(int argc, char **argv);
 
 /* update: check latest release, prompt for index deletion, prompt for ui/standard,
  * download and replace binary. */
+/* True when the installer script (install.sh / install.ps1 on Windows) is
+ * present beside the binary. `update` prints a command built from this;
+ * naming a path that does not exist ends the interaction on a failing
+ * command (#1632). Exposed for testing. */
+bool cbm_cli_installer_beside_binary(const char *dir);
+
 int cbm_cmd_update(int argc, char **argv);
 
 /* config: get/set/list/reset runtime config values. */

tests/test_cli.c

@@ -12636,7 +12636,61 @@ TEST(cli_windows_update_hands_off_to_install_script) {
  *  Suite definition
  * ═══════════════════════════════════════════════════════════════════ */
 
+/* #1632: `update` derives the installer command from the BINARY's directory,
+ * which is not the same question as "is the installer there". A binary in
+ * ~/.local/bin with no install.sh beside it still produced:
+ *
+ *     bash "/home/<user>/.local/bin/install.sh"
+ *     /usr/bin/bash: .../install.sh: No such file or directory
+ *
+ * reported on discussion #1560 by a user already three releases deep in install
+ * trouble. `update` exists to tell someone how to proceed; ending on a command
+ * that cannot run is the one outcome it must not produce. */
+TEST(cli_update_only_names_an_installer_that_exists_issue1632) {
+    char tmpdir[256];
+    snprintf(tmpdir, sizeof(tmpdir), "/tmp/cli-installer-probe-XXXXXX");
+    if (!cbm_mkdtemp(tmpdir)) {
+        FAIL("cbm_mkdtemp failed");
+    }
+#ifdef _WIN32
+    const char *installer = "install.ps1";
+#else
+    const char *installer = "install.sh";
+#endif
+
+    /* A directory holding the binary but no installer must not be advertised. */
+    bool absent_is_refused = !cbm_cli_installer_beside_binary(tmpdir);
+
+    char script[512];
+    snprintf(script, sizeof(script), "%s/%s", tmpdir, installer);
+    write_test_file(script, "#!/bin/sh\nexit 0\n");
+    bool present_is_accepted = cbm_cli_installer_beside_binary(tmpdir);
+
+    /* A directory of that name must not count: `bash <dir>` is not a command. */
+    char decoy[512];
+    snprintf(decoy, sizeof(decoy), "%s/decoy", tmpdir);
+    test_mkdirp(decoy);
+    char decoy_installer[640];
+    snprintf(decoy_installer, sizeof(decoy_installer), "%s/%s", decoy, installer);
+    test_mkdirp(decoy_installer);
+    bool directory_is_refused = !cbm_cli_installer_beside_binary(decoy);
+
+    bool empty_is_refused = !cbm_cli_installer_beside_binary("");
+    test_rmdir_r(tmpdir);
+
+    if (!absent_is_refused)
+        FAIL("a directory with no installer must not be named as one");
+    if (!present_is_accepted)
+        FAIL("an installer that is present must be named");
+    if (!directory_is_refused)
+        FAIL("a DIRECTORY named install.sh is not a runnable installer");
+    if (!empty_is_refused)
+        FAIL("an empty directory string must be refused");
+    PASS();
+}
+
 SUITE(cli) {
+    RUN_TEST(cli_update_only_names_an_installer_that_exists_issue1632);
     RUN_TEST(cli_progress_visibility_policy);
     RUN_TEST(cli_raw_mcp_result_preserves_tool_error_status);
     RUN_TEST(cli_maintenance_cancellation_forces_failure_status);