diff --git a/CHANGELOG.md b/CHANGELOG.md
index f70ed28..c2d8da2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,8 @@ to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ### Fixed
 
+- `htpasswd.entry` and `system.timezone` observe everything their apply sets. The first left a credentials file world-readable whenever its hash already verified; the second left `/etc/timezone` naming another zone whenever the symlink was right. Both reported `already`. Two adverse cases, each seen red on a real machine first (#635, #636).
+
 - A def calling another instruction with too few arguments is refused instead of binding the missing one to the empty string. `file.write(path)` inside a def overwrote the file with nothing and reported `ok.done` — a file destroyed under a success verdict. A plan-level call was always checked on both bounds; only the def side was not (#633).
 
 ## [0.13.0] - 2026-09-09
diff --git a/internal/std/htpasswd/entry.shellf b/internal/std/htpasswd/entry.shellf
index cadcf5d..160f0d0 100644
--- a/internal/std/htpasswd/entry.shellf
+++ b/internal/std/htpasswd/entry.shellf
@@ -24,6 +24,12 @@ def entry(path: str, user: str, password: str) as root {
         u = shell { printf '%s' "$user" | grep -qE '^[A-Za-z0-9_.-]+$' }
         if !u { return err.badUser(u) }
     }
+    # Two fields, because the apply guarantees two things: the credential, and the mode that
+    # keeps it from being world-readable. Observing the hash alone reported `already` over a
+    # correct file at 644 and the `chmod` below never ran (#635) — the shape `sudo.write` and
+    # `sshd.config` already had, and this def did not. The mode is a constant this def chose,
+    # not a parameter, so it is a plain assertion: the awk numeric compare `file.mode` needs
+    # (#543) exists to echo back the *caller's* spelling, and there is no caller here.
     observe {
         return state(valid: shell {
             # The login is matched literally, the way the apply does. `grep "^$user:"` made
@@ -37,7 +43,7 @@ def entry(path: str, user: str, password: str) as root {
             salt=$(printf '%s' "$hash" | cut -d'$' -f3)
             [ -n "$salt" ] || exit 1
             [ "$(printf '%s' "$password" | openssl passwd -apr1 -stdin -salt "$salt")" = "$hash" ]
-        }.exit == 0)
+        }.exit == 0, secured: shell { [ "$(stat -c '%a' "$path" 2>/dev/null)" = "600" ] }.exit == 0)
     }
     apply {
         r = shell {
diff --git a/internal/std/system/timezone.shellf b/internal/std/system/timezone.shellf
index 2f14350..6e1e2b8 100644
--- a/internal/std/system/timezone.shellf
+++ b/internal/std/system/timezone.shellf
@@ -18,10 +18,23 @@ def timezone(zone: str) as root {
         z = shell { test -f "/usr/share/zoneinfo/$zone" }
         if !z { return err.unknownZone(z) }
     }
+    # Both files, because the apply writes both. Reading the link alone reported `already` on
+    # a host whose `/etc/localtime` was right and whose `/etc/timezone` named another zone —
+    # the exact disagreement the comment above says this def exists to prevent (#636).
+    #
+    # `recorded` is a comparison, not the file's contents: a field with no same-named
+    # parameter only has to be truthy, so returning `Europe/Berlin` would converge as happily
+    # as the right answer. `zone` is compared to the argument because a parameter carries
+    # that name; `recorded` cannot be, so it answers yes or no itself.
+    #
+    # On a host that ships no `/etc/timezone` the file simply is not there, the comparison
+    # fails, the apply creates it, and the next run converges — the def does not need to know
+    # whether the distribution is Debian.
     observe {
         # The link's target, not `date +%Z`: an abbreviation like CEST is seasonal and
         # shared by several zones, so comparing it would converge on the wrong continent.
-        return state(zone: shell { readlink -f /etc/localtime | sed 's#^/usr/share/zoneinfo/##' }.stdout)
+        return state(zone: shell { readlink -f /etc/localtime | sed 's#^/usr/share/zoneinfo/##' }.stdout,
+                     recorded: shell { [ "$(cat /etc/timezone 2>/dev/null)" = "$zone" ] }.exit == 0)
     }
     apply {
         r = shell {
diff --git a/test/e2e/adverse-cases.md b/test/e2e/adverse-cases.md
index 11b2e2c..a1922fd 100644
--- a/test/e2e/adverse-cases.md
+++ b/test/e2e/adverse-cases.md
@@ -63,6 +63,15 @@ database that exists under the wrong owner, two logins where one is a regex matc
 other, an archive member emptied in place. Each was verified to fail before the fix and pass after — a case of this kind that
 was never seen red proves nothing at all, since a weak observe passes it by construction.
 
+**And the `apply` must not run for any other reason.** A case of this kind tests the
+`observe`, so the state it builds has to be one the def under test would call converged —
+break anything else as well and the apply runs regardless, taking the assertion with it.
+Both cases in #634 were already asserted by an existing plan and both assertions passed:
+`adverse-htpasswd.entry.shellf:38` asserts mode 600 after a call that changes the password,
+`adverse-system.timezone.shellf:13` asserts `/etc/timezone` after breaking the symlink too.
+Neither could fail, and the defect each was written beside survived underneath it
+from the day the def shipped until #634.
+
 An argument case passes a path holding a space, a single quote and a `&`, or a name at a
 boundary (empty, very long, starting with a dash). It asserts the machine like any other
 case: the directory that exists is the one that was asked for, *whole*, and no sibling was
@@ -73,10 +82,11 @@ ordinary names, which is the point.
 
 ## Coverage, and the gate that is not here yet
 
-8 cases against 38 defs today. A CI gate requiring an adverse case per def would be 30
-named exemptions, which is not a gate — it is a file nobody re-reads, and it turns the
-exemption from a signal into the norm. `def-coverage.sh` works because it is at 38/38.
+28 cases over 22 defs, against 49 defs today. A CI gate requiring an adverse case per def
+would be 27 named exemptions, which is not a gate — it is a file nobody re-reads, and it
+turns the exemption from a signal into the norm. `def-coverage.sh` works because it is at
+48/49, with its single exemption named and argued.
 
-The gate lands when this directory covers the defs that declare an `observe` (~20) — those
+The gate lands when this directory covers the defs that declare an `observe` (34) — those
 are the ones for which "hostile starting state" means anything; an action-shaped def
 (ADR-0029) has no state to get wrong. Until then the protection is #489 staying open.
diff --git a/test/e2e/plans/adverse-htpasswd.entry-mode.shellf b/test/e2e/plans/adverse-htpasswd.entry-mode.shellf
new file mode 100644
index 0000000..79517b8
--- /dev/null
+++ b/test/e2e/plans/adverse-htpasswd.entry-mode.shellf
@@ -0,0 +1,31 @@
+# `htpasswd.entry` observes the mode its own apply sets (#635).
+#
+# Right-shaped but wrong (adverse-cases.md): the credential in the file is **correct** — the
+# stored hash verifies against the password asked for — and the file is world-readable. The
+# observe answered only "does the hash verify", said yes, and the `chmod 600` at the end of
+# the apply never ran. A credentials file at 644, reported converged.
+#
+# Distinct from `adverse-htpasswd.entry.shellf`, which also asserts the mode: there the
+# password differs, so the apply runs and chmods on the way. An assertion the apply always
+# satisfies cannot test an observe. Here the observe must be the thing that decides.
+on target {
+    dir.ensure("/tmp/adv-htpasswd-mode")
+    as root {
+        unsafe shell {
+            # The salt is fixed so the hash is the one this password verifies against — the
+            # file is right, and only the mode is wrong.
+            printf 'covadmin:%s\n' "$(printf 'hunter2' | openssl passwd -apr1 -stdin -salt abcdefgh)" \
+                > /tmp/adv-htpasswd-mode/users
+            chmod 644 /tmp/adv-htpasswd-mode/users
+        }
+        htpasswd.entry("/tmp/adv-htpasswd-mode/users", "covadmin", "hunter2")
+        shell {
+            [ "$(stat -c '%a' /tmp/adv-htpasswd-mode/users)" = "600" ] || exit 1
+            # And the credential still verifies: the repair must not have dropped the line.
+            line=$(grep '^covadmin:' /tmp/adv-htpasswd-mode/users) || exit 1
+            hash=${line#*:}
+            salt=$(printf '%s' "$hash" | cut -d'$' -f3)
+            [ "$(printf 'hunter2' | openssl passwd -apr1 -stdin -salt "$salt")" = "$hash" ] || exit 1
+        }
+    }
+}
diff --git a/test/e2e/plans/adverse-system.timezone-recorded.shellf b/test/e2e/plans/adverse-system.timezone-recorded.shellf
new file mode 100644
index 0000000..601cfd7
--- /dev/null
+++ b/test/e2e/plans/adverse-system.timezone-recorded.shellf
@@ -0,0 +1,23 @@
+# `system.timezone` observes both files its apply writes (#636).
+#
+# Right-shaped but wrong (adverse-cases.md): `/etc/localtime` already points at the wanted
+# zone and `/etc/timezone` holds another one. The observe read the link alone, converged, and
+# left the file — which is what `dpkg-reconfigure tzdata` reads, so the next tzdata upgrade
+# undoes the def.
+#
+# Distinct from `adverse-system.timezone.shellf`, which breaks the link as well: there the
+# apply runs whatever the second file holds, so its assertion on `/etc/timezone` passes
+# without ever testing the observe.
+on target {
+    as root {
+        unsafe shell {
+            ln -sf /usr/share/zoneinfo/Europe/Paris /etc/localtime
+            printf 'Europe/Berlin\n' > /etc/timezone
+        }
+        system.timezone("Europe/Paris")
+        shell {
+            grep -qx 'Europe/Paris' /etc/timezone || exit 1
+            [ "$(readlink -f /etc/localtime)" = "/usr/share/zoneinfo/Europe/Paris" ] || exit 1
+        }
+    }
+}