fix(launcher): recover from broken equal-minor PATH shadows

scripts/loopx-python.sh

@@ -75,11 +75,14 @@ select_loopx_python() {
   fi
 
   while IFS= read -r candidate; do
-    resolved="$(resolve_candidate "${candidate}")"
-    if [ -n "${resolved}" ] && python_version_ok "${resolved}"; then
-      printf '%s\n' "${resolved}"
-      return 0
-    fi
+    # A broken earlier executable must not hide a usable equal-minor runtime.
+    for directory in "${path_directories[@]}"; do
+      resolved="$(resolve_candidate "${directory:-.}/${candidate}")"
+      if [ -n "${resolved}" ] && python_version_ok "${resolved}"; then
+        printf '%s\n' "${resolved}"
+        return 0
+      fi
+    done
   done < <(versioned_python_names "${path_directories[@]}")
 
   resolved="$(resolve_candidate python3)"

tests/control_plane_ts/python_path_discovery.test.ts

@@ -0,0 +1,55 @@
+import assert from "node:assert/strict";
+import { spawnSync } from "node:child_process";
+import { copyFileSync, mkdirSync, mkdtempSync, rmSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import test from "node:test";
+import { fileURLToPath } from "node:url";
+
+import { resolveTestPython } from "../../scripts/test-python.mjs";
+
+const root = fileURLToPath(new URL("../../", import.meta.url));
+const shellPath = (path: string) => process.platform === "win32"
+  ? path.replace(/\\/g, "/").replace(/^([A-Za-z]):/, (_, drive: string) => `/${drive.toLowerCase()}`)
+  : path;
+const quote = (value: string) => `'${value.replace(/'/g, `'"'"'`)}'`;
+
+for (const [name, firstWorks, firstMinor, secondMinor, expected] of [
+  ["broken shadow does not hide a working equal minor", false, 98, 98, "second"],
+  ["equal minors retain PATH precedence", true, 98, 98, "first"],
+  ["higher minor wins across directories", true, 97, 98, "second"],
+  ["broken higher minor falls back to a working lower minor", false, 98, 97, "second"],
+] as const) {
+  test(`Python PATH discovery: ${name}`, t => {
+    const directory = mkdtempSync(join(tmpdir(), "loopx-python-path-"));
+    t.after(() => rmSync(directory, { recursive: true, force: true }));
+    const scripts = join(directory, "scripts");
+    mkdirSync(scripts);
+    copyFileSync(join(root, "scripts/loopx-python.sh"), join(scripts, "loopx-python.sh"));
+    const python = resolveTestPython();
+    const bins = [join(directory, "first bin"), join(directory, "second bin")];
+    for (const [index, minor] of [firstMinor, secondMinor].entries()) {
+      mkdirSync(bins[index]);
+      const label = index === 0 ? "first" : "second";
+      const body = index === 0 && !firstWorks ? "exit 1"
+        : `export LOOPX_SELECTED=${label}\nexec ${quote(shellPath(python))} "$@"`;
+      writeFileSync(join(bins[index], `python3.${minor}`), `#!/bin/sh\n${body}\n`, { mode: 0o755 });
+    }
+    // An older working alias makes an incorrect recovery observable without
+    // depending on a Python executable installed by the host test runner.
+    writeFileSync(join(bins[0], "python3"), `#!/bin/sh\nexport LOOPX_SELECTED=older\nexec ${quote(shellPath(python))} "$@"\n`, { mode: 0o755 });
+    const discovered = spawnSync("bash", ["-c", process.platform === "win32"
+      ? 'cygpath -w "$(command -v bash)"' : "command -v bash"], { encoding: "utf8" });
+    assert.equal(discovered.status, 0, discovered.stderr);
+    const env: NodeJS.ProcessEnv = {
+      ...process.env, HOME: shellPath(directory), PATH: `${bins.map(shellPath).join(":")}:/usr/bin:/bin`,
+    };
+    delete env.LOOPX_PYTHON;
+    const result = spawnSync(discovered.stdout.trim(), [join(scripts, "loopx-python.sh"), "--exec", "-c",
+      "import json,os,sys; print(json.dumps([os.environ['LOOPX_SELECTED'],sys.executable]))"], {
+      cwd: directory, env, encoding: "utf8", timeout: 10_000,
+    });
+    assert.equal(result.status, 0, result.stderr);
+    assert.deepEqual(JSON.parse(result.stdout.trim()), [expected, python]);
+  });
+}