feat: auto-rebase blocked merge queue worktrees

ecc2/src/main.rs

@@ -250,6 +250,9 @@ enum Commands {
         /// Emit machine-readable JSON instead of the human summary
         #[arg(long)]
         json: bool,
+        /// Process the queue, auto-rebasing clean blocked worktrees and merging what becomes ready
+        #[arg(long)]
+        apply: bool,
     },
     /// Prune worktrees for inactive sessions and report any active sessions still holding one
     PruneWorktrees {
@@ -844,7 +847,15 @@ async fn main() -> Result<()> {
                 }
             }
         }
-        Some(Commands::MergeQueue { json }) => {
+        Some(Commands::MergeQueue { json, apply }) => {
+            if apply {
+                let outcome = session::manager::process_merge_queue(&db).await?;
+                if json {
+                    println!("{}", serde_json::to_string_pretty(&outcome)?);
+                } else {
+                    println!("{}", format_bulk_worktree_merge_human(&outcome));
+                }
+            } else {
                 let report = session::manager::build_merge_queue(&db)?;
                 if json {
                     println!("{}", serde_json::to_string_pretty(&report)?);
@@ -852,6 +863,7 @@ async fn main() -> Result<()> {
                     println!("{}", format_merge_queue_human(&report));
                 }
             }
+        }
         Some(Commands::PruneWorktrees { json }) => {
             let outcome = session::manager::prune_inactive_worktrees(&db, &cfg).await?;
             if json {
@@ -1506,6 +1518,26 @@ fn format_bulk_worktree_merge_human(
         ));
     }
 
+    if !outcome.rebased.is_empty() {
+        lines.push(format!(
+            "Rebased {} blocked worktree(s) onto their base branch",
+            outcome.rebased.len()
+        ));
+        for rebased in &outcome.rebased {
+            lines.push(format!(
+                "- rebased {} onto {} for {}{}",
+                rebased.branch,
+                rebased.base_branch,
+                short_session(&rebased.session_id),
+                if rebased.already_up_to_date {
+                    " (already up to date)"
+                } else {
+                    ""
+                }
+            ));
+        }
+    }
+
     if !outcome.active_with_worktree_ids.is_empty() {
         lines.push(format!(
             "Skipped {} active worktree session(s)",
@@ -1524,6 +1556,12 @@ fn format_bulk_worktree_merge_human(
             outcome.dirty_worktree_ids.len()
         ));
     }
+    if !outcome.blocked_by_queue_session_ids.is_empty() {
+        lines.push(format!(
+            "Blocked {} worktree(s) on remaining queue conflicts",
+            outcome.blocked_by_queue_session_ids.len()
+        ));
+    }
     if !outcome.failures.is_empty() {
         lines.push(format!(
             "Encountered {} merge failure(s)",
@@ -2613,7 +2651,24 @@ mod tests {
             .expect("merge-queue --json should parse");
 
         match cli.command {
-            Some(Commands::MergeQueue { json }) => assert!(json),
+            Some(Commands::MergeQueue { json, apply }) => {
+                assert!(json);
+                assert!(!apply);
+            }
+            _ => panic!("expected merge-queue subcommand"),
+        }
+    }
+
+    #[test]
+    fn cli_parses_merge_queue_apply_flag() {
+        let cli = Cli::try_parse_from(["ecc", "merge-queue", "--apply", "--json"])
+            .expect("merge-queue --apply --json should parse");
+
+        match cli.command {
+            Some(Commands::MergeQueue { json, apply }) => {
+                assert!(json);
+                assert!(apply);
+            }
             _ => panic!("expected merge-queue subcommand"),
         }
     }
@@ -2813,9 +2868,16 @@ mod tests {
                 already_up_to_date: false,
                 cleaned_worktree: true,
             }],
+            rebased: vec![session::manager::WorktreeRebaseOutcome {
+                session_id: "rebased12345678".to_string(),
+                branch: "ecc/rebased12345678".to_string(),
+                base_branch: "main".to_string(),
+                already_up_to_date: false,
+            }],
             active_with_worktree_ids: vec!["running12345678".to_string()],
             conflicted_session_ids: vec!["conflict123456".to_string()],
             dirty_worktree_ids: vec!["dirty123456789".to_string()],
+            blocked_by_queue_session_ids: vec!["queue123456789".to_string()],
             failures: vec![session::manager::WorktreeMergeFailure {
                 session_id: "fail1234567890".to_string(),
                 reason: "base branch not checked out".to_string(),
@@ -2824,9 +2886,12 @@ mod tests {
 
         assert!(text.contains("Merged 1 ready worktree(s)"));
         assert!(text.contains("- merged ecc/deadbeefcafefeed -> main for deadbeef"));
+        assert!(text.contains("Rebased 1 blocked worktree(s) onto their base branch"));
+        assert!(text.contains("- rebased ecc/rebased12345678 onto main for rebased1"));
         assert!(text.contains("Skipped 1 active worktree session(s)"));
         assert!(text.contains("Skipped 1 conflicted worktree(s)"));
         assert!(text.contains("Skipped 1 dirty worktree(s)"));
+        assert!(text.contains("Blocked 1 worktree(s) on remaining queue conflicts"));
         assert!(text.contains("Encountered 1 merge failure(s)"));
         assert!(text.contains("- failed fail1234: base branch not checked out"));
     }

ecc2/src/session/daemon.rs

@@ -1202,9 +1202,11 @@ mod tests {
                 invoked_flag.store(true, std::sync::atomic::Ordering::SeqCst);
                 Ok(manager::WorktreeBulkMergeOutcome {
                     merged: Vec::new(),
+                    rebased: Vec::new(),
                     active_with_worktree_ids: Vec::new(),
                     conflicted_session_ids: Vec::new(),
                     dirty_worktree_ids: Vec::new(),
+                    blocked_by_queue_session_ids: Vec::new(),
                     failures: Vec::new(),
                 })
             }
@@ -1239,9 +1241,16 @@ mod tests {
                         cleaned_worktree: true,
                     },
                 ],
+                rebased: vec![manager::WorktreeRebaseOutcome {
+                    session_id: "worker-r".to_string(),
+                    branch: "ecc/worker-r".to_string(),
+                    base_branch: "main".to_string(),
+                    already_up_to_date: false,
+                }],
                 active_with_worktree_ids: vec!["worker-c".to_string()],
                 conflicted_session_ids: vec!["worker-d".to_string()],
                 dirty_worktree_ids: vec!["worker-e".to_string()],
+                blocked_by_queue_session_ids: vec!["worker-f".to_string()],
                 failures: Vec::new(),
             })
         })

ecc2/src/session/manager.rs

@@ -803,6 +803,14 @@ pub struct WorktreeMergeOutcome {
     pub cleaned_worktree: bool,
 }
 
+#[derive(Debug, Clone, Serialize)]
+pub struct WorktreeRebaseOutcome {
+    pub session_id: String,
+    pub branch: String,
+    pub base_branch: String,
+    pub already_up_to_date: bool,
+}
+
 pub async fn merge_session_worktree(
     db: &StateStore,
     id: &str,
@@ -841,6 +849,34 @@ pub async fn merge_session_worktree(
     })
 }
 
+pub async fn rebase_session_worktree(db: &StateStore, id: &str) -> Result<WorktreeRebaseOutcome> {
+    let session = resolve_session(db, id)?;
+
+    if matches!(
+        session.state,
+        SessionState::Pending | SessionState::Running | SessionState::Idle | SessionState::Stale
+    ) {
+        anyhow::bail!(
+            "Cannot rebase active session {} while it is {}",
+            session.id,
+            session.state
+        );
+    }
+
+    let worktree = session
+        .worktree
+        .clone()
+        .ok_or_else(|| anyhow::anyhow!("Session {} has no attached worktree", session.id))?;
+    let outcome = crate::worktree::rebase_onto_base(&worktree)?;
+
+    Ok(WorktreeRebaseOutcome {
+        session_id: session.id,
+        branch: outcome.branch,
+        base_branch: outcome.base_branch,
+        already_up_to_date: outcome.already_up_to_date,
+    })
+}
+
 #[derive(Debug, Clone, Serialize)]
 pub struct WorktreeMergeFailure {
     pub session_id: String,
@@ -850,15 +886,110 @@ pub struct WorktreeMergeFailure {
 #[derive(Debug, Clone, Serialize)]
 pub struct WorktreeBulkMergeOutcome {
     pub merged: Vec<WorktreeMergeOutcome>,
+    pub rebased: Vec<WorktreeRebaseOutcome>,
     pub active_with_worktree_ids: Vec<String>,
     pub conflicted_session_ids: Vec<String>,
     pub dirty_worktree_ids: Vec<String>,
+    pub blocked_by_queue_session_ids: Vec<String>,
     pub failures: Vec<WorktreeMergeFailure>,
 }
 
 pub async fn merge_ready_worktrees(
     db: &StateStore,
     cleanup_worktree: bool,
+) -> Result<WorktreeBulkMergeOutcome> {
+    if cleanup_worktree {
+        return process_merge_queue(db).await;
+    }
+
+    merge_ready_worktrees_one_pass(db, cleanup_worktree).await
+}
+
+pub async fn process_merge_queue(db: &StateStore) -> Result<WorktreeBulkMergeOutcome> {
+    let mut merged = Vec::new();
+    let mut rebased = Vec::new();
+    let mut failures = Vec::new();
+    let mut attempted_rebase_heads = BTreeMap::<String, String>::new();
+
+    loop {
+        let report = build_merge_queue(db)?;
+        let mut merged_any = false;
+
+        for entry in &report.ready_entries {
+            match merge_session_worktree(db, &entry.session_id, true).await {
+                Ok(outcome) => {
+                    merged.push(outcome);
+                    merged_any = true;
+                }
+                Err(error) => failures.push(WorktreeMergeFailure {
+                    session_id: entry.session_id.clone(),
+                    reason: error.to_string(),
+                }),
+            }
+        }
+
+        if merged_any {
+            continue;
+        }
+
+        let mut rebased_any = false;
+        for entry in &report.blocked_entries {
+            if !can_auto_rebase_merge_queue_entry(entry) {
+                continue;
+            }
+
+            let session = resolve_session(db, &entry.session_id)?;
+            let Some(worktree) = session.worktree.clone() else {
+                continue;
+            };
+            let base_head = crate::worktree::branch_head_oid(&worktree, &worktree.base_branch)?;
+            if attempted_rebase_heads
+                .get(&entry.session_id)
+                .is_some_and(|last_head| last_head == &base_head)
+            {
+                continue;
+            }
+            attempted_rebase_heads.insert(entry.session_id.clone(), base_head);
+
+            match rebase_session_worktree(db, &entry.session_id).await {
+                Ok(outcome) => {
+                    rebased.push(outcome);
+                    rebased_any = true;
+                    break;
+                }
+                Err(error) => failures.push(WorktreeMergeFailure {
+                    session_id: entry.session_id.clone(),
+                    reason: error.to_string(),
+                }),
+            }
+        }
+
+        if rebased_any {
+            continue;
+        }
+
+        let (
+            active_with_worktree_ids,
+            conflicted_session_ids,
+            dirty_worktree_ids,
+            blocked_by_queue_session_ids,
+        ) = classify_merge_queue_report(&report);
+
+        return Ok(WorktreeBulkMergeOutcome {
+            merged,
+            rebased,
+            active_with_worktree_ids,
+            conflicted_session_ids,
+            dirty_worktree_ids,
+            blocked_by_queue_session_ids,
+            failures,
+        });
+    }
+}
+
+async fn merge_ready_worktrees_one_pass(
+    db: &StateStore,
+    cleanup_worktree: bool,
 ) -> Result<WorktreeBulkMergeOutcome> {
     let sessions = db.list_sessions()?;
     let mut merged = Vec::new();
@@ -926,9 +1057,11 @@ pub async fn merge_ready_worktrees(
 
     Ok(WorktreeBulkMergeOutcome {
         merged,
+        rebased: Vec::new(),
         active_with_worktree_ids,
         conflicted_session_ids,
         dirty_worktree_ids,
+        blocked_by_queue_session_ids: Vec::new(),
         failures,
     })
 }
@@ -1170,6 +1303,49 @@ pub fn build_merge_queue(db: &StateStore) -> Result<MergeQueueReport> {
     })
 }
 
+fn can_auto_rebase_merge_queue_entry(entry: &MergeQueueEntry) -> bool {
+    !entry.ready_to_merge
+        && !entry.dirty
+        && entry.worktree_health == worktree::WorktreeHealth::Conflicted
+        && !entry.blocked_by.is_empty()
+        && entry
+            .blocked_by
+            .iter()
+            .all(|blocker| blocker.session_id == entry.session_id)
+}
+
+fn classify_merge_queue_report(
+    report: &MergeQueueReport,
+) -> (Vec<String>, Vec<String>, Vec<String>, Vec<String>) {
+    let mut active = Vec::new();
+    let mut conflicted = Vec::new();
+    let mut dirty = Vec::new();
+    let mut queue_blocked = Vec::new();
+
+    for entry in &report.blocked_entries {
+        if entry.blocked_by.iter().any(|blocker| {
+            blocker.session_id == entry.session_id
+                && matches!(
+                    blocker.state,
+                    SessionState::Pending
+                        | SessionState::Running
+                        | SessionState::Idle
+                        | SessionState::Stale
+                )
+        }) {
+            active.push(entry.session_id.clone());
+        } else if entry.dirty {
+            dirty.push(entry.session_id.clone());
+        } else if entry.worktree_health == worktree::WorktreeHealth::Conflicted {
+            conflicted.push(entry.session_id.clone());
+        } else {
+            queue_blocked.push(entry.session_id.clone());
+        }
+    }
+
+    (active, conflicted, dirty, queue_blocked)
+}
+
 pub async fn delete_session(db: &StateStore, id: &str) -> Result<()> {
     let session = resolve_session(db, id)?;
 
@@ -3235,6 +3411,174 @@ mod tests {
         Ok(())
     }
 
+    #[tokio::test(flavor = "current_thread")]
+    async fn process_merge_queue_rebases_blocked_session_and_merges_it() -> Result<()> {
+        let tempdir = TestDir::new("manager-process-merge-queue-success")?;
+        let repo_root = tempdir.path().join("repo");
+        init_git_repo(&repo_root)?;
+
+        let cfg = build_config(tempdir.path());
+        let db = StateStore::open(&cfg.db_path)?;
+        let now = Utc::now();
+
+        let alpha_worktree = worktree::create_for_session_in_repo("alpha", &cfg, &repo_root)?;
+        fs::write(alpha_worktree.path.join("README.md"), "hello\nalpha\n")?;
+        run_git(&alpha_worktree.path, ["commit", "-am", "alpha change"])?;
+
+        let beta_worktree = worktree::create_for_session_in_repo("beta", &cfg, &repo_root)?;
+        fs::write(beta_worktree.path.join("README.md"), "hello\nalpha\n")?;
+        run_git(&beta_worktree.path, ["commit", "-am", "beta shared change"])?;
+        fs::write(beta_worktree.path.join("README.md"), "hello\nalpha\nbeta\n")?;
+        run_git(&beta_worktree.path, ["commit", "-am", "beta follow-up"])?;
+
+        db.insert_session(&Session {
+            id: "alpha".to_string(),
+            task: "alpha merge".to_string(),
+            project: "ecc".to_string(),
+            task_group: "merge".to_string(),
+            agent_type: "claude".to_string(),
+            working_dir: alpha_worktree.path.clone(),
+            state: SessionState::Completed,
+            pid: None,
+            worktree: Some(alpha_worktree.clone()),
+            created_at: now - Duration::minutes(2),
+            updated_at: now - Duration::minutes(2),
+            last_heartbeat_at: now - Duration::minutes(2),
+            metrics: SessionMetrics::default(),
+        })?;
+        db.insert_session(&Session {
+            id: "beta".to_string(),
+            task: "beta merge".to_string(),
+            project: "ecc".to_string(),
+            task_group: "merge".to_string(),
+            agent_type: "claude".to_string(),
+            working_dir: beta_worktree.path.clone(),
+            state: SessionState::Completed,
+            pid: None,
+            worktree: Some(beta_worktree.clone()),
+            created_at: now - Duration::minutes(1),
+            updated_at: now - Duration::minutes(1),
+            last_heartbeat_at: now - Duration::minutes(1),
+            metrics: SessionMetrics::default(),
+        })?;
+
+        let queue_before = build_merge_queue(&db)?;
+        assert_eq!(queue_before.ready_entries.len(), 1);
+        assert_eq!(queue_before.ready_entries[0].session_id, "alpha");
+        assert_eq!(queue_before.blocked_entries.len(), 1);
+        assert_eq!(queue_before.blocked_entries[0].session_id, "beta");
+
+        let outcome = process_merge_queue(&db).await?;
+
+        assert_eq!(
+            outcome
+                .merged
+                .iter()
+                .map(|entry| entry.session_id.as_str())
+                .collect::<Vec<_>>(),
+            vec!["alpha", "beta"]
+        );
+        assert_eq!(outcome.rebased.len(), 1);
+        assert_eq!(outcome.rebased[0].session_id, "beta");
+        assert!(outcome.active_with_worktree_ids.is_empty());
+        assert!(outcome.conflicted_session_ids.is_empty());
+        assert!(outcome.dirty_worktree_ids.is_empty());
+        assert!(outcome.blocked_by_queue_session_ids.is_empty());
+        assert!(outcome.failures.is_empty());
+        assert_eq!(
+            fs::read_to_string(repo_root.join("README.md"))?,
+            "hello\nalpha\nbeta\n"
+        );
+        assert!(db
+            .get_session("alpha")?
+            .context("alpha should still exist")?
+            .worktree
+            .is_none());
+        assert!(db
+            .get_session("beta")?
+            .context("beta should still exist")?
+            .worktree
+            .is_none());
+
+        Ok(())
+    }
+
+    #[tokio::test(flavor = "current_thread")]
+    async fn process_merge_queue_records_failed_rebase_and_leaves_blocked_session() -> Result<()> {
+        let tempdir = TestDir::new("manager-process-merge-queue-fail")?;
+        let repo_root = tempdir.path().join("repo");
+        init_git_repo(&repo_root)?;
+
+        let cfg = build_config(tempdir.path());
+        let db = StateStore::open(&cfg.db_path)?;
+        let now = Utc::now();
+
+        let alpha_worktree = worktree::create_for_session_in_repo("alpha", &cfg, &repo_root)?;
+        fs::write(alpha_worktree.path.join("README.md"), "hello\nalpha\n")?;
+        run_git(&alpha_worktree.path, ["commit", "-am", "alpha change"])?;
+
+        let beta_worktree = worktree::create_for_session_in_repo("beta", &cfg, &repo_root)?;
+        fs::write(beta_worktree.path.join("README.md"), "hello\nbeta\n")?;
+        run_git(&beta_worktree.path, ["commit", "-am", "beta change"])?;
+
+        db.insert_session(&Session {
+            id: "alpha".to_string(),
+            task: "alpha merge".to_string(),
+            project: "ecc".to_string(),
+            task_group: "merge".to_string(),
+            agent_type: "claude".to_string(),
+            working_dir: alpha_worktree.path.clone(),
+            state: SessionState::Completed,
+            pid: None,
+            worktree: Some(alpha_worktree.clone()),
+            created_at: now - Duration::minutes(2),
+            updated_at: now - Duration::minutes(2),
+            last_heartbeat_at: now - Duration::minutes(2),
+            metrics: SessionMetrics::default(),
+        })?;
+        db.insert_session(&Session {
+            id: "beta".to_string(),
+            task: "beta merge".to_string(),
+            project: "ecc".to_string(),
+            task_group: "merge".to_string(),
+            agent_type: "claude".to_string(),
+            working_dir: beta_worktree.path.clone(),
+            state: SessionState::Completed,
+            pid: None,
+            worktree: Some(beta_worktree.clone()),
+            created_at: now - Duration::minutes(1),
+            updated_at: now - Duration::minutes(1),
+            last_heartbeat_at: now - Duration::minutes(1),
+            metrics: SessionMetrics::default(),
+        })?;
+
+        let outcome = process_merge_queue(&db).await?;
+
+        assert_eq!(
+            outcome
+                .merged
+                .iter()
+                .map(|entry| entry.session_id.as_str())
+                .collect::<Vec<_>>(),
+            vec!["alpha"]
+        );
+        assert!(outcome.rebased.is_empty());
+        assert_eq!(outcome.conflicted_session_ids, vec!["beta".to_string()]);
+        assert!(outcome.active_with_worktree_ids.is_empty());
+        assert!(outcome.dirty_worktree_ids.is_empty());
+        assert!(outcome.blocked_by_queue_session_ids.is_empty());
+        assert_eq!(outcome.failures.len(), 1);
+        assert_eq!(outcome.failures[0].session_id, "beta");
+        assert!(outcome.failures[0].reason.contains("git rebase failed"));
+        assert!(db
+            .get_session("beta")?
+            .context("beta should still exist")?
+            .worktree
+            .is_some());
+
+        Ok(())
+    }
+
     #[tokio::test(flavor = "current_thread")]
     async fn build_merge_queue_orders_ready_sessions_and_blocks_conflicts() -> Result<()> {
         let tempdir = TestDir::new("manager-merge-queue")?;

ecc2/src/tui/dashboard.rs

@@ -2734,9 +2734,11 @@ impl Dashboard {
             Ok(outcome) => {
                 self.refresh();
                 if outcome.merged.is_empty()
+                    && outcome.rebased.is_empty()
                     && outcome.active_with_worktree_ids.is_empty()
                     && outcome.conflicted_session_ids.is_empty()
                     && outcome.dirty_worktree_ids.is_empty()
+                    && outcome.blocked_by_queue_session_ids.is_empty()
                     && outcome.failures.is_empty()
                 {
                     self.set_operator_note("no ready worktrees to merge".to_string());
@@ -2744,6 +2746,9 @@ impl Dashboard {
                 }
 
                 let mut parts = vec![format!("merged {} ready worktree(s)", outcome.merged.len())];
+                if !outcome.rebased.is_empty() {
+                    parts.push(format!("rebased {}", outcome.rebased.len()));
+                }
                 if !outcome.active_with_worktree_ids.is_empty() {
                     parts.push(format!(
                         "skipped {} active",
@@ -2762,6 +2767,12 @@ impl Dashboard {
                         outcome.dirty_worktree_ids.len()
                     ));
                 }
+                if !outcome.blocked_by_queue_session_ids.is_empty() {
+                    parts.push(format!(
+                        "blocked {} in queue",
+                        outcome.blocked_by_queue_session_ids.len()
+                    ));
+                }
                 if !outcome.failures.is_empty() {
                     parts.push(format!("{} failed", outcome.failures.len()));
                 }

ecc2/src/worktree/mod.rs

@@ -35,6 +35,13 @@ pub struct MergeOutcome {
     pub already_up_to_date: bool,
 }
 
+#[derive(Debug, Clone, Serialize, PartialEq, Eq)]
+pub struct RebaseOutcome {
+    pub branch: String,
+    pub base_branch: String,
+    pub already_up_to_date: bool,
+}
+
 #[derive(Debug, Clone, Serialize, PartialEq, Eq)]
 pub struct BranchConflictPreview {
     pub left_branch: String,
@@ -741,6 +748,65 @@ pub fn merge_into_base(worktree: &WorktreeInfo) -> Result<MergeOutcome> {
     })
 }
 
+pub fn rebase_onto_base(worktree: &WorktreeInfo) -> Result<RebaseOutcome> {
+    if has_uncommitted_changes(worktree)? {
+        anyhow::bail!(
+            "Worktree {} has uncommitted changes; commit or discard them before rebasing",
+            worktree.branch
+        );
+    }
+
+    let repo_root = base_checkout_path(worktree)?;
+    let before_head = branch_head_oid_in_repo(&repo_root, &worktree.branch)?;
+    let output = Command::new("git")
+        .arg("-C")
+        .arg(&worktree.path)
+        .args(["rebase", &worktree.base_branch])
+        .output()
+        .context("Failed to rebase worktree branch onto base")?;
+
+    if !output.status.success() {
+        let abort_output = Command::new("git")
+            .arg("-C")
+            .arg(&worktree.path)
+            .args(["rebase", "--abort"])
+            .output()
+            .context("Failed to abort unsuccessful rebase")?;
+        let abort_warning = if abort_output.status.success() {
+            String::new()
+        } else {
+            format!(
+                " (rebase abort warning: {})",
+                String::from_utf8_lossy(&abort_output.stderr).trim()
+            )
+        };
+        let stderr = format!(
+            "{}\n{}",
+            String::from_utf8_lossy(&output.stdout),
+            String::from_utf8_lossy(&output.stderr)
+        );
+        anyhow::bail!("git rebase failed: {}{}", stderr.trim(), abort_warning);
+    }
+
+    let after_head = branch_head_oid_in_repo(&repo_root, &worktree.branch)?;
+    let rebase_output = format!(
+        "{}\n{}",
+        String::from_utf8_lossy(&output.stdout),
+        String::from_utf8_lossy(&output.stderr)
+    );
+
+    Ok(RebaseOutcome {
+        branch: worktree.branch.clone(),
+        base_branch: worktree.base_branch.clone(),
+        already_up_to_date: before_head == after_head || rebase_output.contains("up to date"),
+    })
+}
+
+pub fn branch_head_oid(worktree: &WorktreeInfo, branch: &str) -> Result<String> {
+    let repo_root = base_checkout_path(worktree)?;
+    branch_head_oid_in_repo(&repo_root, branch)
+}
+
 fn git_diff_shortstat(worktree_path: &Path, extra_args: &[&str]) -> Result<Option<String>> {
     let mut command = Command::new("git");
     command
@@ -1113,6 +1179,22 @@ fn git_status_short(worktree_path: &Path) -> Result<Vec<String>> {
     Ok(parse_nonempty_lines(&output.stdout))
 }
 
+fn branch_head_oid_in_repo(repo_root: &Path, branch: &str) -> Result<String> {
+    let output = Command::new("git")
+        .arg("-C")
+        .arg(repo_root)
+        .args(["rev-parse", branch])
+        .output()
+        .context("Failed to resolve branch head")?;
+
+    if !output.status.success() {
+        let stderr = String::from_utf8_lossy(&output.stderr);
+        anyhow::bail!("git rev-parse failed: {stderr}");
+    }
+
+    Ok(String::from_utf8_lossy(&output.stdout).trim().to_string())
+}
+
 fn validate_branch_name(repo_root: &Path, branch: &str) -> Result<()> {
     let output = Command::new("git")
         .arg("-C")
@@ -1567,6 +1649,130 @@ mod tests {
         Ok(())
     }
 
+    #[test]
+    fn rebase_onto_base_replays_simple_branch_after_base_advances() -> Result<()> {
+        let root =
+            std::env::temp_dir().join(format!("ecc2-worktree-rebase-success-{}", Uuid::new_v4()));
+        let repo = init_repo(&root)?;
+
+        let alpha_dir = root.join("wt-alpha");
+        run_git(
+            &repo,
+            &[
+                "worktree",
+                "add",
+                "-b",
+                "ecc/alpha",
+                alpha_dir.to_str().expect("utf8 path"),
+                "HEAD",
+            ],
+        )?;
+        fs::write(alpha_dir.join("README.md"), "hello\nalpha\n")?;
+        run_git(&alpha_dir, &["commit", "-am", "alpha change"])?;
+
+        let beta_dir = root.join("wt-beta");
+        run_git(
+            &repo,
+            &[
+                "worktree",
+                "add",
+                "-b",
+                "ecc/beta",
+                beta_dir.to_str().expect("utf8 path"),
+                "HEAD",
+            ],
+        )?;
+        fs::write(beta_dir.join("README.md"), "hello\nalpha\n")?;
+        run_git(&beta_dir, &["commit", "-am", "beta shared change"])?;
+        fs::write(beta_dir.join("README.md"), "hello\nalpha\nbeta\n")?;
+        run_git(&beta_dir, &["commit", "-am", "beta follow-up"])?;
+
+        run_git(&repo, &["merge", "--no-edit", "ecc/alpha"])?;
+
+        let beta = WorktreeInfo {
+            path: beta_dir.clone(),
+            branch: "ecc/beta".to_string(),
+            base_branch: "main".to_string(),
+        };
+        let readiness_before = merge_readiness(&beta)?;
+        assert_eq!(readiness_before.status, MergeReadinessStatus::Conflicted);
+
+        let outcome = rebase_onto_base(&beta)?;
+        assert_eq!(outcome.branch, "ecc/beta");
+        assert_eq!(outcome.base_branch, "main");
+        assert!(!outcome.already_up_to_date);
+
+        let readiness_after = merge_readiness(&beta)?;
+        assert_eq!(readiness_after.status, MergeReadinessStatus::Ready);
+        assert_eq!(
+            fs::read_to_string(beta_dir.join("README.md"))?,
+            "hello\nalpha\nbeta\n"
+        );
+
+        let _ = Command::new("git")
+            .arg("-C")
+            .arg(&repo)
+            .args(["worktree", "remove", "--force"])
+            .arg(&alpha_dir)
+            .output();
+        let _ = Command::new("git")
+            .arg("-C")
+            .arg(&repo)
+            .args(["worktree", "remove", "--force"])
+            .arg(&beta_dir)
+            .output();
+        let _ = fs::remove_dir_all(root);
+        Ok(())
+    }
+
+    #[test]
+    fn rebase_onto_base_aborts_failed_rebase() -> Result<()> {
+        let root =
+            std::env::temp_dir().join(format!("ecc2-worktree-rebase-fail-{}", Uuid::new_v4()));
+        let repo = init_repo(&root)?;
+
+        let worktree_dir = root.join("wt-conflict");
+        run_git(
+            &repo,
+            &[
+                "worktree",
+                "add",
+                "-b",
+                "ecc/conflict",
+                worktree_dir.to_str().expect("utf8 path"),
+                "HEAD",
+            ],
+        )?;
+
+        fs::write(worktree_dir.join("README.md"), "hello\nbranch\n")?;
+        run_git(&worktree_dir, &["commit", "-am", "branch change"])?;
+        fs::write(repo.join("README.md"), "hello\nmain\n")?;
+        run_git(&repo, &["commit", "-am", "main change"])?;
+
+        let info = WorktreeInfo {
+            path: worktree_dir.clone(),
+            branch: "ecc/conflict".to_string(),
+            base_branch: "main".to_string(),
+        };
+
+        let error = rebase_onto_base(&info).expect_err("rebase should fail");
+        assert!(error.to_string().contains("git rebase failed"));
+        assert!(git_status_short(&worktree_dir)?.is_empty());
+        assert_eq!(
+            merge_readiness(&info)?.status,
+            MergeReadinessStatus::Conflicted
+        );
+
+        let _ = Command::new("git")
+            .arg("-C")
+            .arg(&repo)
+            .args(["worktree", "remove", "--force"])
+            .arg(&worktree_dir)
+            .output();
+        let _ = fs::remove_dir_all(root);
+        Ok(())
+    }
+
     #[test]
     fn branch_conflict_preview_reports_conflicting_branches() -> Result<()> {
         let root = std::env::temp_dir().join(format!(