fix(bins): Windows-safe GIT_CEILING join; next-version probes the full default-base chain

GIT_CEILING_DIRECTORIES was joined with ':' — git on Windows splits on
';' and drive letters contain ':', silently disabling the #2144
second-layer defense there; now path.delimiter. next-version's
default-base detection only tried origin/HEAD then 'main', diverging
from the canonical 4-step chain diff-scope uses — origin/main and
origin/master probes added, pinned by fixture repos.

bin/gstack-memory-ingest.ts

@@ -54,7 +54,7 @@ import {
   rmSync,
   realpathSync,
 } from "fs";
-import { join, basename, dirname } from "path";
+import { join, basename, dirname, delimiter } from "path";
 import { execFileSync, spawnSync, spawn, type ChildProcess } from "child_process";
 import { homedir } from "os";
 import { createHash } from "crypto";
@@ -1443,8 +1443,10 @@ function runGbrainImport(
     }
     const baseEnv: NodeJS.ProcessEnv = {
       ...process.env,
+      // path.delimiter, not ':' — git splits this on ';' on Windows, and
+      // drive-letter paths contain ':' themselves.
       GIT_CEILING_DIRECTORIES: process.env.GIT_CEILING_DIRECTORIES
-        ? `${ceiling}:${process.env.GIT_CEILING_DIRECTORIES}`
+        ? `${ceiling}${delimiter}${process.env.GIT_CEILING_DIRECTORIES}`
         : ceiling,
     };
     const child = spawnGbrainAsync(

bin/gstack-next-version

@@ -407,13 +407,29 @@ function parseArgs(argv: string[]): { base: string; bump: Bump; current: string;
   if (help) return { base: "", bump: "micro", current: "", excludePR: null, help: true };
   if (!base) {
     // Detect the default branch instead of assuming main (local-only repos
-    // on trunk/master work like GitHub repos on main).
+    // on trunk/master work like GitHub repos on main). Same probe order as
+    // the canonical chain in bin/gstack-diff-scope and {{BASE_BRANCH_DETECT}}
+    // (scripts/resolvers/utility.ts): origin/HEAD -> origin/main ->
+    // origin/master -> literal "main". origin/HEAD is unset on plain clones
+    // that never ran `git remote set-head`, so the rev-parse probes matter.
     try {
       const head = execFileSync("git", ["symbolic-ref", "refs/remotes/origin/HEAD"], { encoding: "utf-8", stdio: ["ignore", "pipe", "ignore"] }).trim();
-      base = head.replace("refs/remotes/origin/", "") || "main";
+      base = head.replace("refs/remotes/origin/", "");
     } catch {
-      base = "main";
+      // fall through to the rev-parse probes
     }
+    if (!base) {
+      for (const candidate of ["main", "master"]) {
+        try {
+          execFileSync("git", ["rev-parse", "--verify", "-q", `origin/${candidate}`], { stdio: ["ignore", "ignore", "ignore"] });
+          base = candidate;
+          break;
+        } catch {
+          // probe failed; try the next candidate
+        }
+      }
+    }
+    if (!base) base = "main";
   }
   if (!bump) {
     console.error("Error: --bump is required (major|minor|patch|micro)");