diff --git a/src-tauri/migrations/004_default_agents.sql b/src-tauri/migrations/004_default_agents.sql
new file mode 100644
index 0000000..0a2807e
--- /dev/null
+++ b/src-tauri/migrations/004_default_agents.sql
@@ -0,0 +1,33 @@
+ALTER TABLE agents ADD COLUMN is_default INTEGER NOT NULL DEFAULT 0;
+
+CREATE UNIQUE INDEX IF NOT EXISTS idx_agents_default_per_role
+ON agents(role)
+WHERE is_default = 1;
+
+INSERT INTO agents (id, name, role, tool, custom_prompt, is_default, created_at, updated_at)
+SELECT
+    'default-analyst-agent',
+    'Default Analyst',
+    'analyst',
+    'codex',
+    '',
+    1,
+    datetime('now'),
+    datetime('now')
+WHERE NOT EXISTS (
+    SELECT 1 FROM agents WHERE role = 'analyst' AND is_default = 1
+);
+
+INSERT INTO agents (id, name, role, tool, custom_prompt, is_default, created_at, updated_at)
+SELECT
+    'default-developer-agent',
+    'Default Developer',
+    'developer',
+    'claude_code',
+    '',
+    1,
+    datetime('now'),
+    datetime('now')
+WHERE NOT EXISTS (
+    SELECT 1 FROM agents WHERE role = 'developer' AND is_default = 1
+);
diff --git a/src-tauri/src/db.rs b/src-tauri/src/db.rs
index 68a1224..dac524e 100644
--- a/src-tauri/src/db.rs
+++ b/src-tauri/src/db.rs
@@ -4,6 +4,7 @@ use std::path::Path;
 const MIGRATION_001: &str = include_str!("../migrations/001_init.sql");
 const MIGRATION_002: &str = include_str!("../migrations/002_add_last_polled.sql");
 const MIGRATION_003: &str = include_str!("../migrations/003_add_agents.sql");
+const MIGRATION_004: &str = include_str!("../migrations/004_default_agents.sql");
 
 pub fn init(db_path: &Path) -> Result<Connection> {
     let conn = Connection::open(db_path)?;
@@ -41,6 +42,10 @@ fn migrate(conn: &Connection) -> Result<()> {
         conn.execute_batch(MIGRATION_003)?;
         conn.pragma_update(None, "user_version", 3)?;
     }
+    if version < 4 {
+        conn.execute_batch(MIGRATION_004)?;
+        conn.pragma_update(None, "user_version", 4)?;
+    }
 
     Ok(())
 }
@@ -92,6 +97,29 @@ mod tests {
         let version: i32 = conn
             .pragma_query_value(None, "user_version", |row| row.get(0))
             .unwrap();
-        assert_eq!(version, 3);
+        assert_eq!(version, 4);
+    }
+
+    #[test]
+    fn test_default_agents_are_seeded() {
+        let conn = init_in_memory().expect("should initialize");
+
+        let analyst_defaults: i32 = conn
+            .query_row(
+                "SELECT COUNT(*) FROM agents WHERE role = 'analyst' AND is_default = 1",
+                [],
+                |row| row.get(0),
+            )
+            .unwrap();
+        let developer_defaults: i32 = conn
+            .query_row(
+                "SELECT COUNT(*) FROM agents WHERE role = 'developer' AND is_default = 1",
+                [],
+                |row| row.get(0),
+            )
+            .unwrap();
+
+        assert_eq!(analyst_defaults, 1);
+        assert_eq!(developer_defaults, 1);
     }
 }
diff --git a/src-tauri/src/models/agent.rs b/src-tauri/src/models/agent.rs
index 7a44192..87be266 100644
--- a/src-tauri/src/models/agent.rs
+++ b/src-tauri/src/models/agent.rs
@@ -1,7 +1,10 @@
-use rusqlite::{params, Connection, Result};
+use rusqlite::{params, Connection, OptionalExtension, Result};
 use serde::{Deserialize, Serialize};
 use uuid::Uuid;
 
+pub const DEFAULT_ANALYST_AGENT_ID: &str = "default-analyst-agent";
+pub const DEFAULT_DEVELOPER_AGENT_ID: &str = "default-developer-agent";
+
 #[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq)]
 #[serde(rename_all = "snake_case")]
 pub enum AgentRole {
@@ -70,6 +73,7 @@ pub struct Agent {
     pub role: AgentRole,
     pub tool: AgentTool,
     pub custom_prompt: String,
+    pub is_default: bool,
     pub created_at: String,
     pub updated_at: String,
 }
@@ -77,6 +81,7 @@ pub struct Agent {
 fn from_row(row: &rusqlite::Row) -> rusqlite::Result<Agent> {
     let role_raw: String = row.get(2)?;
     let tool_raw: String = row.get(3)?;
+    let is_default_int: i32 = row.get(5)?;
 
     Ok(Agent {
         id: row.get(0)?,
@@ -84,8 +89,9 @@ fn from_row(row: &rusqlite::Row) -> rusqlite::Result<Agent> {
         role: AgentRole::from_str(&role_raw)?,
         tool: AgentTool::from_str(&tool_raw)?,
         custom_prompt: row.get(4)?,
-        created_at: row.get(5)?,
-        updated_at: row.get(6)?,
+        is_default: is_default_int != 0,
+        created_at: row.get(6)?,
+        updated_at: row.get(7)?,
     })
 }
 
@@ -101,7 +107,7 @@ impl Agent {
         let now = chrono::Utc::now().to_rfc3339();
 
         conn.execute(
-            "INSERT INTO agents (id, name, role, tool, custom_prompt, created_at, updated_at) VALUES (?1, ?2, ?3, ?4, ?5, ?6, ?7)",
+            "INSERT INTO agents (id, name, role, tool, custom_prompt, is_default, created_at, updated_at) VALUES (?1, ?2, ?3, ?4, ?5, 0, ?6, ?7)",
             params![id, name, role.as_str(), tool.as_str(), custom_prompt, now, now],
         )?;
 
@@ -111,6 +117,7 @@ impl Agent {
             role,
             tool,
             custom_prompt: custom_prompt.to_string(),
+            is_default: false,
             created_at: now.clone(),
             updated_at: now,
         })
@@ -118,7 +125,9 @@ impl Agent {
 
     pub fn list(conn: &Connection) -> Result<Vec<Agent>> {
         let mut stmt = conn.prepare(
-            "SELECT id, name, role, tool, custom_prompt, created_at, updated_at FROM agents ORDER BY role ASC, created_at DESC",
+            "SELECT id, name, role, tool, custom_prompt, is_default, created_at, updated_at
+             FROM agents
+             ORDER BY role ASC, is_default DESC, created_at DESC",
         )?;
         let rows = stmt.query_map([], from_row)?;
         rows.collect()
@@ -126,12 +135,23 @@ impl Agent {
 
     pub fn get_by_id(conn: &Connection, id: &str) -> Result<Agent> {
         conn.query_row(
-            "SELECT id, name, role, tool, custom_prompt, created_at, updated_at FROM agents WHERE id = ?1",
+            "SELECT id, name, role, tool, custom_prompt, is_default, created_at, updated_at FROM agents WHERE id = ?1",
             params![id],
             from_row,
         )
     }
 
+    pub fn get_default_by_role(conn: &Connection, role: AgentRole) -> Result<Agent> {
+        conn.query_row(
+            "SELECT id, name, role, tool, custom_prompt, is_default, created_at, updated_at
+             FROM agents
+             WHERE role = ?1 AND is_default = 1
+             LIMIT 1",
+            params![role.as_str()],
+            from_row,
+        )
+    }
+
     pub fn update(
         conn: &Connection,
         id: &str,
@@ -140,7 +160,23 @@ impl Agent {
         tool: AgentTool,
         custom_prompt: &str,
     ) -> Result<()> {
+        let existing = Self::get_by_id(conn, id)?;
         let now = chrono::Utc::now().to_rfc3339();
+
+        if existing.is_default {
+            if existing.name != name || existing.role != role || existing.tool != tool {
+                return Err(rusqlite::Error::InvalidParameterName(
+                    "Default agents cannot change name, role, or tool".to_string(),
+                ));
+            }
+
+            conn.execute(
+                "UPDATE agents SET custom_prompt = ?1, updated_at = ?2 WHERE id = ?3",
+                params![custom_prompt, now, id],
+            )?;
+            return Ok(());
+        }
+
         let affected = conn.execute(
             "UPDATE agents SET name = ?1, role = ?2, tool = ?3, custom_prompt = ?4, updated_at = ?5 WHERE id = ?6",
             params![name, role.as_str(), tool.as_str(), custom_prompt, now, id],
@@ -154,16 +190,50 @@ impl Agent {
     }
 
     pub fn delete(conn: &Connection, id: &str) -> Result<()> {
+        let agent = Self::get_by_id(conn, id)?;
+
+        if agent.is_default {
+            return Err(rusqlite::Error::InvalidParameterName(
+                "Default agents cannot be deleted".to_string(),
+            ));
+        }
+
+        let default_agent_id: String = conn
+            .query_row(
+                "SELECT id FROM agents WHERE role = ?1 AND is_default = 1 LIMIT 1",
+                params![agent.role.as_str()],
+                |row| row.get(0),
+            )
+            .optional()?
+            .ok_or_else(|| {
+                rusqlite::Error::InvalidParameterName(format!(
+                    "No default agent found for role '{}'",
+                    agent.role.as_str()
+                ))
+            })?;
+
+        match agent.role {
+            AgentRole::Analyst => {
+                conn.execute(
+                    "UPDATE watched_trackers SET analyst_agent_id = ?1 WHERE analyst_agent_id = ?2",
+                    params![default_agent_id, id],
+                )?;
+            }
+            AgentRole::Developer => {
+                conn.execute(
+                    "UPDATE watched_trackers SET developer_agent_id = ?1 WHERE developer_agent_id = ?2",
+                    params![default_agent_id, id],
+                )?;
+            }
+        }
+
         conn.execute(
             "UPDATE watched_trackers
-             SET analyst_agent_id = CASE WHEN analyst_agent_id = ?1 THEN NULL ELSE analyst_agent_id END,
-                 developer_agent_id = CASE WHEN developer_agent_id = ?1 THEN NULL ELSE developer_agent_id END,
-                 status = CASE
-                     WHEN analyst_agent_id = ?1 OR developer_agent_id = ?1 THEN 'invalid'
-                     ELSE status
-                 END
-             WHERE analyst_agent_id = ?1 OR developer_agent_id = ?1",
-            params![id],
+             SET status = CASE
+                 WHEN analyst_agent_id IS NULL OR developer_agent_id IS NULL THEN 'invalid'
+                 ELSE 'valid'
+             END",
+            [],
         )?;
 
         let affected = conn.execute("DELETE FROM agents WHERE id = ?1", params![id])?;
@@ -185,6 +255,19 @@ mod tests {
         db::init_in_memory().expect("db init should succeed")
     }
 
+    #[test]
+    fn test_defaults_exist() {
+        let conn = setup();
+
+        let analyst = Agent::get_default_by_role(&conn, AgentRole::Analyst).unwrap();
+        let developer = Agent::get_default_by_role(&conn, AgentRole::Developer).unwrap();
+
+        assert_eq!(analyst.id, DEFAULT_ANALYST_AGENT_ID);
+        assert_eq!(developer.id, DEFAULT_DEVELOPER_AGENT_ID);
+        assert!(analyst.is_default);
+        assert!(developer.is_default);
+    }
+
     #[test]
     fn test_insert_and_get_agent() {
         let conn = setup();
@@ -204,59 +287,61 @@ mod tests {
         assert_eq!(found.role, AgentRole::Analyst);
         assert_eq!(found.tool, AgentTool::Codex);
         assert_eq!(found.custom_prompt, "Focus on root cause.");
+        assert!(!found.is_default);
     }
 
     #[test]
-    fn test_update_agent() {
+    fn test_update_default_agent_allows_prompt_only() {
         let conn = setup();
+        let analyst = Agent::get_default_by_role(&conn, AgentRole::Analyst).unwrap();
 
-        let created = Agent::insert(
+        let err = Agent::update(
             &conn,
-            "Dev Claude",
+            &analyst.id,
+            "Renamed",
             AgentRole::Developer,
             AgentTool::ClaudeCode,
-            "",
+            "new script",
         )
-        .unwrap();
+        .unwrap_err();
+        assert!(
+            err.to_string()
+                .contains("Default agents cannot change name, role, or tool")
+        );
 
         Agent::update(
             &conn,
-            &created.id,
-            "Dev Codex",
-            AgentRole::Developer,
-            AgentTool::Codex,
-            "Write tests.",
+            &analyst.id,
+            &analyst.name,
+            analyst.role.clone(),
+            analyst.tool.clone(),
+            "Prompt override",
         )
         .unwrap();
 
-        let updated = Agent::get_by_id(&conn, &created.id).unwrap();
-        assert_eq!(updated.name, "Dev Codex");
-        assert_eq!(updated.tool, AgentTool::Codex);
-        assert_eq!(updated.custom_prompt, "Write tests.");
+        let updated = Agent::get_by_id(&conn, &analyst.id).unwrap();
+        assert_eq!(updated.custom_prompt, "Prompt override");
     }
 
     #[test]
-    fn test_delete_agent_invalidates_trackers() {
+    fn test_delete_default_agent_is_rejected() {
+        let conn = setup();
+        let analyst = Agent::get_default_by_role(&conn, AgentRole::Analyst).unwrap();
+
+        let err = Agent::delete(&conn, &analyst.id).unwrap_err();
+        assert!(err.to_string().contains("Default agents cannot be deleted"));
+    }
+
+    #[test]
+    fn test_delete_agent_reassigns_trackers_to_default() {
         let conn = setup();
         let project = Project::insert(&conn, "P", "/tmp/p", None, "main").unwrap();
 
-        let analyst = Agent::insert(
-            &conn,
-            "Analyst",
-            AgentRole::Analyst,
-            AgentTool::Codex,
-            "",
-        )
-        .unwrap();
+        let analyst_default = Agent::get_default_by_role(&conn, AgentRole::Analyst).unwrap();
+        let developer_default = Agent::get_default_by_role(&conn, AgentRole::Developer).unwrap();
 
-        let developer = Agent::insert(
-            &conn,
-            "Developer",
-            AgentRole::Developer,
-            AgentTool::ClaudeCode,
-            "",
-        )
-        .unwrap();
+        let analyst = Agent::insert(&conn, "Analyst", AgentRole::Analyst, AgentTool::Codex, "")
+            .unwrap();
 
         let tracker = WatchedTracker::insert(
             &conn,
@@ -265,7 +350,7 @@ mod tests {
             "Bugs",
             10,
             &analyst.id,
-            &developer.id,
+            &developer_default.id,
             vec![],
         )
         .unwrap();
@@ -273,8 +358,14 @@ mod tests {
         Agent::delete(&conn, &analyst.id).unwrap();
 
         let reloaded = WatchedTracker::get_by_id(&conn, &tracker.id).unwrap();
-        assert_eq!(reloaded.status, "invalid");
-        assert!(reloaded.analyst_agent_id.is_none());
-        assert_eq!(reloaded.developer_agent_id.as_deref(), Some(developer.id.as_str()));
+        assert_eq!(reloaded.status, "valid");
+        assert_eq!(
+            reloaded.analyst_agent_id.as_deref(),
+            Some(analyst_default.id.as_str())
+        );
+        assert_eq!(
+            reloaded.developer_agent_id.as_deref(),
+            Some(developer_default.id.as_str())
+        );
     }
 }
diff --git a/src/components/agents/AgentForm.tsx b/src/components/agents/AgentForm.tsx
index 6a12ec2..d40cb2e 100644
--- a/src/components/agents/AgentForm.tsx
+++ b/src/components/agents/AgentForm.tsx
@@ -13,6 +13,7 @@ export default function AgentForm() {
   const [role, setRole] = useState<AgentRole>("analyst");
   const [tool, setTool] = useState<AgentTool>("codex");
   const [customPrompt, setCustomPrompt] = useState("");
+  const [isDefaultAgent, setIsDefaultAgent] = useState(false);
   const [error, setError] = useState<string | null>(null);
   const [loading, setLoading] = useState(false);
   const [initializing, setInitializing] = useState(false);
@@ -28,6 +29,7 @@ export default function AgentForm() {
         setRole(agent.role);
         setTool(agent.tool);
         setCustomPrompt(agent.custom_prompt);
+        setIsDefaultAgent(agent.is_default);
       } catch (err: unknown) {
         setError(getErrorMessage(err));
       } finally {
@@ -63,6 +65,11 @@ export default function AgentForm() {
 
       <form onSubmit={handleSubmit} className="space-y-4">
         {initializing && <div className="text-sm text-gray-500">Loading agent...</div>}
+        {isEditing && isDefaultAgent && (
+          <div className="rounded border border-blue-200 bg-blue-50 p-3 text-sm text-blue-700">
+            This is a default agent. Only its script/prompt can be modified.
+          </div>
+        )}
 
         <div>
           <label className="mb-1 block text-sm font-medium text-gray-700">Name</label>
@@ -70,6 +77,7 @@ export default function AgentForm() {
             type="text"
             value={name}
             onChange={(e) => setName(e.target.value)}
+            disabled={isEditing && isDefaultAgent}
             required
             className="w-full rounded border border-gray-300 px-3 py-2 text-sm focus:outline-none focus:ring-2 focus:ring-blue-500"
           />
@@ -80,6 +88,7 @@ export default function AgentForm() {
           <select
             value={role}
             onChange={(e) => setRole(e.target.value as AgentRole)}
+            disabled={isEditing && isDefaultAgent}
             className="w-full rounded border border-gray-300 px-3 py-2 text-sm focus:outline-none focus:ring-2 focus:ring-blue-500"
           >
             <option value="analyst">Analyst</option>
@@ -92,6 +101,7 @@ export default function AgentForm() {
           <select
             value={tool}
             onChange={(e) => setTool(e.target.value as AgentTool)}
+            disabled={isEditing && isDefaultAgent}
             className="w-full rounded border border-gray-300 px-3 py-2 text-sm focus:outline-none focus:ring-2 focus:ring-blue-500"
           >
             <option value="codex">Codex</option>
@@ -101,7 +111,7 @@ export default function AgentForm() {
 
         <div>
           <label className="mb-1 block text-sm font-medium text-gray-700">
-            Custom prompt (appended to built-in prompt)
+            Script / custom prompt (appended to built-in prompt)
           </label>
           <textarea
             rows={12}
diff --git a/src/components/agents/AgentList.tsx b/src/components/agents/AgentList.tsx
index ff02510..ba0388f 100644
--- a/src/components/agents/AgentList.tsx
+++ b/src/components/agents/AgentList.tsx
@@ -84,6 +84,11 @@ export default function AgentList() {
             <div className="min-w-0 flex-1">
               <div className="flex items-center gap-2">
                 <span className="text-sm font-medium">{agent.name}</span>
+                {agent.is_default && (
+                  <span className="rounded-full bg-emerald-100 px-2 py-0.5 text-xs text-emerald-700">
+                    Default
+                  </span>
+                )}
                 <span className="rounded-full bg-gray-100 px-2 py-0.5 text-xs text-gray-600">
                   {roleLabel(agent.role)}
                 </span>
@@ -107,13 +112,15 @@ export default function AgentList() {
               >
                 Edit
               </Link>
-              <button
-                type="button"
-                onClick={() => setAgentToDelete(agent)}
-                className="rounded bg-red-100 px-3 py-1 text-xs text-red-700 hover:bg-red-200"
-              >
-                Delete
-              </button>
+              {!agent.is_default && (
+                <button
+                  type="button"
+                  onClick={() => setAgentToDelete(agent)}
+                  className="rounded bg-red-100 px-3 py-1 text-xs text-red-700 hover:bg-red-200"
+                >
+                  Delete
+                </button>
+              )}
             </div>
           </div>
         ))}
@@ -122,7 +129,7 @@ export default function AgentList() {
       <ConfirmModal
         isOpen={agentToDelete !== null}
         title="Delete agent"
-        message="Delete this agent? Trackers using it will become invalid until reconfigured."
+        message="Delete this agent? Trackers using it will be reassigned to the default agent for the same role."
         confirmLabel={deleting ? "Deleting..." : "Delete"}
         confirmDisabled={deleting}
         onCancel={() => {
diff --git a/src/lib/types.ts b/src/lib/types.ts
index e41ed8b..5f19422 100644
--- a/src/lib/types.ts
+++ b/src/lib/types.ts
@@ -22,6 +22,7 @@ export interface Agent {
   role: AgentRole;
   tool: AgentTool;
   custom_prompt: string;
+  is_default: boolean;
   created_at: string;
   updated_at: string;
 }