diff --git a/.claude/memory/MEMORY.md b/.claude/memory/MEMORY.md
index 3a614743d1..f80f36dc5b 100644
--- a/.claude/memory/MEMORY.md
+++ b/.claude/memory/MEMORY.md
@@ -14,3 +14,4 @@ skill.
 - [racket-ui via shadcn](rac-ui-shadcn.md) — the proven recipe to replace the foundation with racket-ui (`markmals/racket-ui`) via the shadcn CLI; **gated on committing `registry.json` to that repo's root**
 - [Apple scaffold](apple-scaffold.md) — the `apple` stack + the `swift-package`/`swift-cli` sibling library stacks: verify=headless Core/package, the swift event-stream command, the dynamic-module/static-dir `path:` trick, `.tmpl`-for-substitution-only, the `.scenario()` binding, packless-stack handling
 - [Mise monorepo](mise-monorepo.md) — generated root config invariant; the unstable-parser comment-preserving merge; the family↔member drift coupling
+- [Fork & upstream](fork-and-upstream.md) — markmals/spec-kit is a FORK of github/spec-kit; gh/PR ops default to the upstream, so target the fork with `-R markmals/spec-kit`
diff --git a/.claude/memory/fork-and-upstream.md b/.claude/memory/fork-and-upstream.md
new file mode 100644
index 0000000000..b6d2b729ac
--- /dev/null
+++ b/.claude/memory/fork-and-upstream.md
@@ -0,0 +1,32 @@
+---
+description: markmals/spec-kit is a FORK of github/spec-kit — gh and PR operations default to the upstream parent, so always target the fork explicitly.
+---
+
+# Fork & upstream
+
+`markmals/spec-kit` (this repo) is a **fork** of `github/spec-kit` (GitHub's
+official Spec-Kit). The fork relationship keeps biting agents who forget it:
+
+- **`gh pr create` defaults the base to the upstream parent** (`github/spec-kit`),
+  not this fork. It fails with `No commits between main and <branch>` /
+  `Head sha can't be blank`, or silently tries to open a PR against GitHub's repo.
+  Always target the fork explicitly:
+
+  ```sh
+  gh pr create -R markmals/spec-kit --base main --head <branch>
+  ```
+
+  Or set it once per clone so every `gh` command defaults correctly:
+
+  ```sh
+  gh repo set-default markmals/spec-kit
+  ```
+
+- Same `-R markmals/spec-kit` caveat for **any** cross-fork `gh` op (`gh pr list`,
+  `gh issue`, `gh api`) — without it you read/write the upstream by accident.
+
+- The git remote is `markmals/spec-kit`, but GitHub redirects the older name
+  `markmals/speckit`, so `gh`/PR URLs may show either spelling — same repo.
+
+PRs here are **fork-internal** (`markmals/spec-kit` `main` <- branch); we do not
+PR up to `github/spec-kit`.