diff --git a/.huskies/.gitignore b/.huskies/.gitignore
index 62fd2d7b..1282a42a 100644
--- a/.huskies/.gitignore
+++ b/.huskies/.gitignore
@@ -35,3 +35,6 @@ double_timmy_log.md
 pipeline.db
 pipeline.db.bak*
 session_store.json
+
+# Full untruncated merge attempt reports (one file per attempt, pruned automatically)
+merge_reports/
diff --git a/server/src/io/fs/project.rs b/server/src/io/fs/project.rs
index 91ef1015..af11fac1 100644
--- a/server/src/io/fs/project.rs
+++ b/server/src/io/fs/project.rs
@@ -5,7 +5,7 @@ use serde_json::json;
 use std::fs;
 use std::path::PathBuf;
 
-use super::scaffold::scaffold_story_kit;
+use super::scaffold::{ensure_gitignore_entries, scaffold_story_kit};
 
 const KEY_LAST_PROJECT: &str = "last_project_path";
 const KEY_KNOWN_PROJECTS: &str = "known_projects";
@@ -36,6 +36,10 @@ pub(crate) async fn ensure_project_root_with_story_kit(
         }
         if !path.join(".huskies").is_dir() {
             scaffold_story_kit(&path, port)?;
+        } else {
+            // Already-adopted project: pick up any Story Kit gitignore entries
+            // added since this project was first scaffolded.
+            ensure_gitignore_entries(&path)?;
         }
         // Always update .mcp.json with the current port so the bot connects to
         // the right endpoint even when HUSKIES_PORT changes between restarts.
@@ -449,6 +453,34 @@ mod tests {
         assert!(project_dir.join(".huskies").is_dir());
     }
 
+    /// Regression test for story 1219: projects scaffolded before
+    /// `merge_reports/` and `session_store.json` were added to the ignore
+    /// list must pick up those entries the next time the project is opened,
+    /// without needing to be re-scaffolded from scratch.
+    #[tokio::test]
+    async fn open_project_retrofits_gitignore_entries_for_existing_project() {
+        let dir = tempdir().unwrap();
+        let project_dir = dir.path().join("myproject");
+        let sk_dir = project_dir.join(".huskies");
+        fs::create_dir_all(&sk_dir).unwrap();
+        fs::write(sk_dir.join(".gitignore"), "worktrees/\n").unwrap();
+        let store = make_store(&dir);
+        let state = SessionState::default();
+
+        open_project(
+            project_dir.to_string_lossy().to_string(),
+            &state,
+            &store,
+            3001,
+        )
+        .await
+        .unwrap();
+
+        let content = fs::read_to_string(sk_dir.join(".gitignore")).unwrap();
+        assert!(content.contains("merge_reports/"));
+        assert!(content.contains("session_store.json"));
+    }
+
     #[tokio::test]
     async fn open_project_does_not_overwrite_existing_story_kit() {
         let dir = tempdir().unwrap();
diff --git a/server/src/io/fs/scaffold/helpers.rs b/server/src/io/fs/scaffold/helpers.rs
index 32a01a0b..5b88b526 100644
--- a/server/src/io/fs/scaffold/helpers.rs
+++ b/server/src/io/fs/scaffold/helpers.rs
@@ -64,6 +64,8 @@ pub(super) fn write_story_kit_gitignore(root: &Path) -> Result<(), String> {
         "store.json",
         "pipeline.db",
         "*.db",
+        "merge_reports/",
+        "session_store.json",
     ];
 
     let gitignore_path = root.join(".huskies").join(".gitignore");
diff --git a/server/src/io/fs/scaffold/mod.rs b/server/src/io/fs/scaffold/mod.rs
index b2acc1c8..ed7c19c9 100644
--- a/server/src/io/fs/scaffold/mod.rs
+++ b/server/src/io/fs/scaffold/mod.rs
@@ -20,6 +20,16 @@ use templates::{
     STORY_KIT_STACK,
 };
 
+/// Retrofit the Story Kit `.gitignore` entries onto a project that was
+/// scaffolded before those entries existed (e.g. `merge_reports/` or
+/// `session_store.json` added in a later release). Idempotent — only
+/// appends lines that are missing, so it is safe to call on every project
+/// open regardless of how old the project's `.huskies/` directory is.
+pub(crate) fn ensure_gitignore_entries(root: &Path) -> Result<(), String> {
+    write_story_kit_gitignore(root)?;
+    append_root_gitignore_entries(root)
+}
+
 pub(crate) fn scaffold_story_kit(root: &Path, port: u16) -> Result<(), String> {
     let story_kit_root = root.join(".huskies");
     let specs_root = story_kit_root.join("specs");
diff --git a/server/src/io/fs/scaffold/tests.rs b/server/src/io/fs/scaffold/tests.rs
index b0aa63a6..2e44990d 100644
--- a/server/src/io/fs/scaffold/tests.rs
+++ b/server/src/io/fs/scaffold/tests.rs
@@ -334,6 +334,31 @@ fn scaffold_creates_story_kit_gitignore_with_relative_entries() {
     // Database files must be ignored so novice users don't accidentally commit them
     assert!(sk_content.contains("pipeline.db"));
     assert!(sk_content.contains("*.db"));
+    // Runtime artifacts written under .huskies/ must be ignored too (story 1219)
+    assert!(sk_content.contains("merge_reports/"));
+    assert!(sk_content.contains("session_store.json"));
+}
+
+#[test]
+fn ensure_gitignore_entries_retrofits_already_adopted_project() {
+    // Simulate a project scaffolded before merge_reports/ and session_store.json
+    // were added to the ignore list: .huskies/.gitignore exists but lacks them.
+    let dir = tempdir().unwrap();
+    fs::create_dir_all(dir.path().join(".huskies")).unwrap();
+    fs::write(
+        dir.path().join(".huskies/.gitignore"),
+        "worktrees/\ncoverage/\n",
+    )
+    .unwrap();
+
+    ensure_gitignore_entries(dir.path()).unwrap();
+
+    let sk_content = fs::read_to_string(dir.path().join(".huskies/.gitignore")).unwrap();
+    assert!(sk_content.contains("merge_reports/"));
+    assert!(sk_content.contains("session_store.json"));
+    // Pre-existing entries must survive untouched
+    assert!(sk_content.contains("worktrees/"));
+    assert!(sk_content.contains("coverage/"));
 }
 
 #[test]