diff --git a/tools/run-plan.sh b/tools/run-plan.sh
index 1aa473f..d5e808e 100755
--- a/tools/run-plan.sh
+++ b/tools/run-plan.sh
@@ -45,9 +45,10 @@ for task in "$plan"/[0-9][0-9]-*.md; do
     # shellcheck disable=SC2086
     # </dev/null: OpenCode 1.15 reads a piped stdin as extra prompt and waits for EOF, so a
     # backgrounded driver would hang before the first model request (2026-09-25).
-    if ! opencode run -m "$model" $flags --title "$milestone/$name" "$prompt" </dev/null \
+    # timeout: a looping session (P5a task 06 ran 3 h) ends at SESSION_MAX seconds (default 90 min).
+    if ! timeout "${SESSION_MAX:-5400}" opencode run -m "$model" $flags --title "$milestone/$name" "$prompt" </dev/null \
         > "$runs/$name.log" 2>&1; then
-        echo "run-plan: opencode exited with an error in $name; see $runs/$name.log" >&2
+        echo "run-plan: opencode exited with an error (or hit SESSION_MAX) in $name; see $runs/$name.log" >&2
         exit 1
     fi
     echo "=== $milestone/$name: session ended $(date '+%H:%M:%S')"