diff --git a/migrations/008_fk_constraints.sql b/migrations/008_fk_constraints.sql
new file mode 100644
index 00000000..d52420f2
--- /dev/null
+++ b/migrations/008_fk_constraints.sql
@@ -0,0 +1,91 @@
+-- Migration 008: Add foreign key constraints to convergence_trajectories and worktrees
+--
+-- Fixes #61: convergence_trajectories and worktrees have no FK reference to tasks(id),
+-- causing orphaned rows when tasks are deleted.
+--
+-- SQLite does not support ALTER TABLE to add FK constraints, so we must
+-- recreate the tables. Data is preserved via INSERT...SELECT.
+
+-- ============================================================================
+-- 1. convergence_trajectories: add REFERENCES tasks(id) ON DELETE CASCADE
+-- ============================================================================
+
+CREATE TABLE IF NOT EXISTS convergence_trajectories_new (
+    id TEXT PRIMARY KEY,
+    task_id TEXT NOT NULL REFERENCES tasks(id) ON DELETE CASCADE,
+    goal_id TEXT,
+    phase TEXT NOT NULL DEFAULT 'preparing',
+    total_fresh_starts INTEGER NOT NULL DEFAULT 0,
+    specification_json TEXT NOT NULL DEFAULT '{}',
+    observations_json TEXT NOT NULL DEFAULT '[]',
+    attractor_state_json TEXT NOT NULL DEFAULT '{}',
+    budget_json TEXT NOT NULL DEFAULT '{}',
+    policy_json TEXT NOT NULL DEFAULT '{}',
+    strategy_log_json TEXT NOT NULL DEFAULT '[]',
+    context_health_json TEXT NOT NULL DEFAULT '{}',
+    hints_json TEXT NOT NULL DEFAULT '[]',
+    forced_strategy_json TEXT,
+    created_at TEXT NOT NULL,
+    updated_at TEXT NOT NULL
+);
+
+-- Copy existing data (skip orphans whose task_id no longer exists)
+INSERT OR IGNORE INTO convergence_trajectories_new
+SELECT ct.*
+FROM convergence_trajectories ct
+INNER JOIN tasks t ON ct.task_id = t.id;
+
+-- Swap tables
+DROP TABLE IF EXISTS convergence_trajectories;
+ALTER TABLE convergence_trajectories_new RENAME TO convergence_trajectories;
+
+-- Recreate indexes
+CREATE INDEX IF NOT EXISTS idx_convergence_trajectories_task_id ON convergence_trajectories(task_id);
+CREATE INDEX IF NOT EXISTS idx_convergence_trajectories_goal_id ON convergence_trajectories(goal_id);
+CREATE INDEX IF NOT EXISTS idx_convergence_trajectories_updated_at ON convergence_trajectories(updated_at);
+CREATE INDEX IF NOT EXISTS idx_convergence_trajectories_phase ON convergence_trajectories(phase);
+
+-- ============================================================================
+-- 2. worktrees: add REFERENCES tasks(id) ON DELETE SET NULL
+-- ============================================================================
+-- Using SET NULL instead of CASCADE because worktree cleanup should be
+-- handled explicitly (files on disk need removal). Setting task_id to NULL
+-- signals "orphaned worktree" without losing the worktree record.
+
+CREATE TABLE IF NOT EXISTS worktrees_new (
+    id TEXT PRIMARY KEY,
+    task_id TEXT REFERENCES tasks(id) ON DELETE SET NULL,
+    path TEXT NOT NULL UNIQUE,
+    branch TEXT NOT NULL,
+    base_ref TEXT NOT NULL,
+    status TEXT NOT NULL DEFAULT 'creating',
+    merge_commit TEXT,
+    error_message TEXT,
+    created_at TEXT NOT NULL DEFAULT (datetime('now')),
+    updated_at TEXT NOT NULL DEFAULT (datetime('now')),
+    completed_at TEXT
+);
+
+INSERT OR IGNORE INTO worktrees_new
+SELECT * FROM worktrees;
+
+DROP TABLE IF EXISTS worktrees;
+ALTER TABLE worktrees_new RENAME TO worktrees;
+
+CREATE INDEX IF NOT EXISTS idx_worktrees_task ON worktrees(task_id);
+CREATE INDEX IF NOT EXISTS idx_worktrees_status ON worktrees(status);
+
+-- ============================================================================
+-- 3. Clean up any existing orphaned agent_instances referencing deleted tasks
+-- ============================================================================
+-- agent_instances.current_task_id is ephemeral runtime state, so we just
+-- NULL it out for rows referencing nonexistent tasks.
+
+UPDATE agent_instances
+SET current_task_id = NULL
+WHERE current_task_id IS NOT NULL
+  AND current_task_id NOT IN (SELECT id FROM tasks);
+
+-- Record migration
+INSERT OR IGNORE INTO schema_migrations (version, description)
+VALUES (8, 'Add FK constraints to convergence_trajectories and worktrees, clean orphaned agent_instances');
diff --git a/src/adapters/sqlite/migrations.rs b/src/adapters/sqlite/migrations.rs
index 69eeea8e..0271dbb3 100644
--- a/src/adapters/sqlite/migrations.rs
+++ b/src/adapters/sqlite/migrations.rs
@@ -119,5 +119,10 @@ pub fn all_embedded_migrations() -> Vec<Migration> {
             description: "Refinement requests persistence for evolution loop".to_string(),
             sql: include_str!("../../../migrations/007_refinement_requests.sql").to_string(),
         },
+        Migration {
+            version: 8,
+            description: "FK constraints on convergence_trajectories and worktrees".to_string(),
+            sql: include_str!("../../../migrations/008_fk_constraints.sql").to_string(),
+        },
     ]
 }