diff --git a/site/package.json b/site/package.json
index 92750d20..cfbe4d37 100644
--- a/site/package.json
+++ b/site/package.json
@@ -16,5 +16,6 @@
     "@astrojs/starlight": "^0.41.3",
     "astro": "^7.0.2",
     "sharp": "^0.34.5"
-  }
+  },
+  "packageManager": "pnpm@10.20.0"
 }
diff --git a/wiki/log/2026-07-11-site-package-manager-pin.md b/wiki/log/2026-07-11-site-package-manager-pin.md
new file mode 100644
index 00000000..2845e1dd
--- /dev/null
+++ b/wiki/log/2026-07-11-site-package-manager-pin.md
@@ -0,0 +1,23 @@
+# Pin the site package manager
+
+```
+Type: log
+```
+
+- **Intent:** stop every automatic site publication from modifying the primary
+  checkout after a successful landing.
+- **Found:** Corepack saw no `packageManager` declaration in
+  `site/package.json`, inserted its current pnpm identity during
+  `tools/site-build.sh`, and left `main` dirty after `tools/task.sh finish`.
+  The build and deployment succeeded, but the next task could not land until
+  an agent manually reverted the unrelated mutation.
+- **Changed:** declared `pnpm@10.20.0`, the project runtime already in use, as
+  the site's package manager. This turns Corepack's repeated implicit mutation
+  into reviewed repository state.
+- **Checks:** `./tools/site-build.sh`; clean-diff audit proving the build made no
+  additional tracked changes; `./tools/check.sh --docs`.
+- **Design/spec impact:** none. This is a deployment hygiene repair for the
+  automatic publication path.
+- **Defense:** a successful publication must leave the canonical checkout
+  usable by the next serialized landing; generated tool metadata cannot become
+  recurring coordination debt.
diff --git a/wiki/log/DEVLOG.md b/wiki/log/DEVLOG.md
index 2116e828..e3f5c0a4 100644
--- a/wiki/log/DEVLOG.md
+++ b/wiki/log/DEVLOG.md
@@ -56,6 +56,11 @@ add or amend a session log, then re-run the generator.
 - Intent: (see session log)
 - Log: [wiki/log/2026-07-11-surveillance-policy.md](2026-07-11-surveillance-policy.md)
 
+## 2026-07-11 - Pin the site package manager
+
+- Intent: (see session log)
+- Log: [wiki/log/2026-07-11-site-package-manager-pin.md](2026-07-11-site-package-manager-pin.md)
+
 ## 2026-07-11 - Simulation characterization baseline
 
 - Intent: `Sim` is about to move out of an eleven-thousand-line source file. Before any behavior changes address, the refactor needs an executable definition of "same simulation": complete persisted state must match after uninterrupted and save/load-resumed command sequences, and the fi...