diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index d32bfd81..90d7fb35 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -128,7 +128,7 @@ repos:
       - id: sandbox-env-reserved-parity
         name: reserved sandbox_env set stays in sync
         language: system
-        files: ^(generator/src/tend/config\.py|proxy/setup-sandbox\.sh)$
+        files: ^(generator/src/tend/config\.py|proxy/setup-sandbox\.sh|docs/tend\.example\.yaml)$
         entry: python3
         args:
           - -c
@@ -154,6 +154,17 @@ repos:
             heredoc_keys = set(re.findall(r'^([A-Za-z_][A-Za-z0-9_]*)=', heredoc, re.M))
             heredoc_keys |= set(re.findall(r'ANTHROPIC_DUMMY="([A-Za-z_][A-Za-z0-9_]*)=', sh))
 
+            # The adopter only meets this set as a rejection at `init`, so the
+            # `sandbox_env` docs have to name every member — a key reserved in
+            # code but absent from the docs reads as settable right up until
+            # the run fails. Scope the search to that bullet: file-wide, an
+            # unrelated mention elsewhere (the auth section names
+            # ANTHROPIC_API_KEY and CLAUDE_CODE_OAUTH_TOKEN) would stand in for
+            # the list entry and hide the drift this leg exists to catch.
+            docs = open("docs/tend.example.yaml").read()
+            section = re.search(r"^# - `sandbox_env`:(.*?)^# - `", docs, re.S | re.M).group(1)
+            documented = set(re.findall(r"`([A-Za-z_][A-Za-z0-9_]*)`", section))
+
             problems = []
             for name in sorted(config_set - shell_set):
                 problems.append(f"'{name}' is reserved in config.py but NOT guarded in setup-sandbox.sh")
@@ -161,15 +172,18 @@ repos:
                 problems.append(f"'{name}' is guarded in setup-sandbox.sh but NOT reserved in config.py")
             for name in sorted(heredoc_keys - config_set):
                 problems.append(f"'{name}' is written to AGENT_ENV_FILE but NOT reserved in config.py — an adopter's sandbox_env could shadow it")
+            for name in sorted(config_set - documented):
+                problems.append(f"'{name}' is reserved in config.py but NOT named in docs/tend.example.yaml's sandbox_env list")
 
             for p in problems:
                 print(p)
             if problems:
                 print(
                     "\nERROR: the reserved sandbox_env set drifted between "
-                    "config.py, setup-sandbox.sh, and the AGENT_ENV_FILE "
-                    "heredoc. The shell case is the security boundary; keep "
-                    "every env-file key reserved and the two sets aligned."
+                    "config.py, setup-sandbox.sh, the AGENT_ENV_FILE heredoc, "
+                    "and docs/tend.example.yaml. The shell case is the security "
+                    "boundary; keep every env-file key reserved, the two sets "
+                    "aligned, and every reserved name documented."
                 )
                 sys.exit(1)
         pass_filenames: false
diff --git a/docs/tend.example.yaml b/docs/tend.example.yaml
index c7a0b987..c934ded1 100644
--- a/docs/tend.example.yaml
+++ b/docs/tend.example.yaml
@@ -183,8 +183,19 @@ bot_name: my-project-bot
 #       - ~/.cargo/bin
 #
 # - `sandbox_env`: NAME: VALUE pairs added to the agent's launch env. Reserved
-#   keys (proxy routing, CA trust, dummy credentials, PATH) are rejected — use
-#   `sandbox_path` for PATH:
+#   keys are rejected at `init`, and again inside the sandbox so a hand-edited
+#   workflow can't smuggle one past:
+#
+#   - proxy routing — `HTTP_PROXY`, `HTTPS_PROXY`, `NO_PROXY`, `http_proxy`,
+#     `https_proxy`, `no_proxy`
+#   - CA trust — `NODE_EXTRA_CA_CERTS`, `SSL_CERT_FILE`, `REQUESTS_CA_BUNDLE`
+#   - dummy credentials — `GH_TOKEN`, `GITHUB_TOKEN`, `ANTHROPIC_API_KEY`,
+#     `CLAUDE_CODE_OAUTH_TOKEN`
+#   - prompt suppression — `CLAUDE_CODE_REMOTE`
+#   - the sandbox's own locations — `HOME`, `PATH`, `XDG_CONFIG_HOME`,
+#     `XDG_CACHE_HOME`, `XDG_DATA_HOME`, `XDG_STATE_HOME`
+#
+#   Use `sandbox_path` to extend PATH:
 #
 #     sandbox_env:
 #       RUST_BACKTRACE: "1"
diff --git a/plugins/install-tend/skills/install-tend/references/tend.example.yaml b/plugins/install-tend/skills/install-tend/references/tend.example.yaml
index c7a0b987..c934ded1 100644
--- a/plugins/install-tend/skills/install-tend/references/tend.example.yaml
+++ b/plugins/install-tend/skills/install-tend/references/tend.example.yaml
@@ -183,8 +183,19 @@ bot_name: my-project-bot
 #       - ~/.cargo/bin
 #
 # - `sandbox_env`: NAME: VALUE pairs added to the agent's launch env. Reserved
-#   keys (proxy routing, CA trust, dummy credentials, PATH) are rejected — use
-#   `sandbox_path` for PATH:
+#   keys are rejected at `init`, and again inside the sandbox so a hand-edited
+#   workflow can't smuggle one past:
+#
+#   - proxy routing — `HTTP_PROXY`, `HTTPS_PROXY`, `NO_PROXY`, `http_proxy`,
+#     `https_proxy`, `no_proxy`
+#   - CA trust — `NODE_EXTRA_CA_CERTS`, `SSL_CERT_FILE`, `REQUESTS_CA_BUNDLE`
+#   - dummy credentials — `GH_TOKEN`, `GITHUB_TOKEN`, `ANTHROPIC_API_KEY`,
+#     `CLAUDE_CODE_OAUTH_TOKEN`
+#   - prompt suppression — `CLAUDE_CODE_REMOTE`
+#   - the sandbox's own locations — `HOME`, `PATH`, `XDG_CONFIG_HOME`,
+#     `XDG_CACHE_HOME`, `XDG_DATA_HOME`, `XDG_STATE_HOME`
+#
+#   Use `sandbox_path` to extend PATH:
 #
 #     sandbox_env:
 #       RUST_BACKTRACE: "1"