State the Checks API gap instead of prescribing an impossible tick

Fine-grained tokens have no Checks permission. GitHub's permission reference
lists no Checks section and no check-run endpoint, and checks is absent from
the token form's pre-fill parameters, so the earlier instruction to tick
Checks: Read asked for a box that does not exist. A token created with every
listed permission still could not read check runs, which is what surfaced this.

The prompt now states the consequence rather than offering a remedy: gh pr
checks reports commit statuses only and gh run view returns no annotations.
Both degrade to empty output rather than a permission error, so without the
note they read as a broken CI integration. Job logs are unaffected; they fall
under Actions, which is granted.

secret_scanning_alerts and vulnerability_alerts move into the pre-filled URL,
leaving nothing for the operator to tick beyond repository selection.

tasks/ai/sbx

@@ -40,13 +40,13 @@ TOKEN_URL_PERMISSIONS=(
     vulnerability_alerts=read
 )
 
-# "checks" is the one permission the agent needs that GitHub omits from the
-# pre-fill parameters, so it has to be ticked by hand. Each entry names what
-# breaks without it, because an unticked box fails later as an empty result or
-# a 403 rather than as a permission error.
-TOKEN_MANUAL_PERMISSIONS=(
-    "Checks: Read    - without it 'gh pr checks' reports no status rollup and"
-    "                  'gh run view' returns no annotations"
+# Fine-grained tokens cannot reach the Checks API at all: GitHub's permission
+# reference has no Checks section and lists no check-run endpoint, so there is
+# no box to tick. Both calls below degrade to empty output rather than a
+# permission error, which reads as broken CI unless it is called out.
+TOKEN_LIMITATIONS=(
+    "gh pr checks     shows only commit statuses, not check runs"
+    "gh run view      returns no annotations"
 )
 
 usage() {
@@ -205,17 +205,20 @@ Create a fine-grained token for $REPOSITORY.
 Everything except the repository is pre-filled. On the page:
 
   1. Repository access -> Only select repositories -> ${REPOSITORY#*/}
-  2. Under Permissions -> Repository permissions, tick the one the form
-     cannot pre-fill:
+  2. Generate token, then paste it below.
+
+Every permission is pre-filled. Fine-grained tokens cannot read check runs,
+so inside the sandbox:
 EOF
 
-    local permission
-    for permission in "${TOKEN_MANUAL_PERMISSIONS[@]}"; do
-        printf '       %s\n' "$permission" >&2
+    local limitation
+    for limitation in "${TOKEN_LIMITATIONS[@]}"; do
+        printf '  %s\n' "$limitation" >&2
     done
 
-    cat >&2 <<EOF
-  3. Generate token, then paste it below.
+    cat >&2 <<'EOF'
+
+A 403 will name what it wanted in the X-Accepted-GitHub-Permissions header.
 
 EOF