feat(session): persist assistant reasoning content

crates/tinyagents-session/src/lib.rs

@@ -79,8 +79,9 @@ pub use tinyagents_harness::error::{Result, TinyAgentsError};
 
 pub use ops::{
     DEFAULT_FTS_SNIPPET_BYTES, fts_snippet_bytes, get_session, list_children, list_messages,
-    list_sessions, list_tool_calls, mark_interrupted, record_message, record_session_end,
-    record_session_start, record_tool_call, search_sessions, set_fts_snippet_bytes,
+    list_sessions, list_tool_calls, mark_interrupted, record_message,
+    record_message_with_reasoning, record_session_end, record_session_start, record_tool_call,
+    search_sessions, set_fts_snippet_bytes,
 };
 pub use retention::{
     RetentionReport, apply_retention, prune_run_events_before, prune_run_telemetry_before,

crates/tinyagents-session/src/migrations.rs

@@ -241,6 +241,8 @@ pub(super) const MIGRATIONS: &[&str] = &[
      CREATE INDEX IF NOT EXISTS idx_agent_teams_updated ON agent_teams(updated_at);
      CREATE INDEX IF NOT EXISTS idx_agent_team_tasks_order
         ON agent_team_tasks(team_id, order_index, created_at);",
+    // ---- 4: retain hidden assistant reasoning ---------------------------
+    "ALTER TABLE session_messages ADD COLUMN reasoning_content TEXT;",
 ];
 
 /// Applies every migration newer than the database's recorded schema version.
@@ -325,7 +327,7 @@ mod test {
     fn migration_list_is_append_only() {
         assert_eq!(
             MIGRATIONS.len(),
-            4,
+            5,
             "MIGRATIONS is append-only — adding one is fine, reordering or \
              deleting one silently re-numbers every later migration"
         );

crates/tinyagents-session/src/ops.rs

@@ -133,6 +133,36 @@ pub fn record_message(
     input_tokens: Option<u64>,
     output_tokens: Option<u64>,
     cost_usd: Option<f64>,
+) -> Result<i64> {
+    record_message_with_reasoning(
+        workspace_dir,
+        session_id,
+        role,
+        content,
+        None,
+        model,
+        input_tokens,
+        output_tokens,
+        cost_usd,
+    )
+}
+
+/// Record a session message together with provider-exposed hidden reasoning.
+///
+/// The historical [`record_message`] API deliberately remains visible-text
+/// only. Hosts that retain a structured assistant message should use this
+/// variant so a tool-call turn does not discard its thinking trace.
+#[allow(clippy::too_many_arguments)]
+pub fn record_message_with_reasoning(
+    workspace_dir: &Path,
+    session_id: &str,
+    role: &str,
+    content: &str,
+    reasoning_content: Option<&str>,
+    model: Option<&str>,
+    input_tokens: Option<u64>,
+    output_tokens: Option<u64>,
+    cost_usd: Option<f64>,
 ) -> Result<i64> {
     let now = Utc::now();
     tinyagents_tracing::trace!(
@@ -149,13 +179,14 @@ pub fn record_message(
     with_transaction(workspace_dir, |conn| {
         conn.execute(
             "INSERT INTO session_messages (
-                session_id, role, content, model,
+                session_id, role, content, reasoning_content, model,
                 input_tokens, output_tokens, cost_usd, created_at
-             ) VALUES (?1, ?2, ?3, ?4, ?5, ?6, ?7, ?8)",
+             ) VALUES (?1, ?2, ?3, ?4, ?5, ?6, ?7, ?8, ?9)",
             params![
                 session_id,
                 role,
                 content,
+                reasoning_content.filter(|value| !value.trim().is_empty()),
                 model,
                 input_tokens.map(|v| v as i64),
                 output_tokens.map(|v| v as i64),
@@ -456,7 +487,7 @@ pub fn list_messages(
     with_connection(workspace_dir, |conn| {
         let lim = limit.unwrap_or(200).min(1000) as i64;
         let mut stmt = conn.prepare(
-            "SELECT id, session_id, role, content, model,
+            "SELECT id, session_id, role, content, reasoning_content, model,
                     input_tokens, output_tokens, cost_usd, created_at
              FROM session_messages
              WHERE session_id = ?1
@@ -470,11 +501,12 @@ pub fn list_messages(
                 session_id: row.get(1)?,
                 role: row.get(2)?,
                 content: row.get(3)?,
-                model: row.get(4)?,
-                input_tokens: row.get::<_, Option<i64>>(5)?.map(|v| v as u64),
-                output_tokens: row.get::<_, Option<i64>>(6)?.map(|v| v as u64),
-                cost_usd: row.get(7)?,
-                created_at: parse_rfc3339(&row.get::<_, String>(8)?)
+                reasoning_content: row.get(4)?,
+                model: row.get(5)?,
+                input_tokens: row.get::<_, Option<i64>>(6)?.map(|v| v as u64),
+                output_tokens: row.get::<_, Option<i64>>(7)?.map(|v| v as u64),
+                cost_usd: row.get(8)?,
+                created_at: parse_rfc3339(&row.get::<_, String>(9)?)
                     .map_err(sql_conversion_error)?,
             })
         })?;

crates/tinyagents-session/src/test.rs

@@ -554,6 +554,46 @@ fn public_session_operations_round_trip_every_record_kind() {
     assert!(ended.ended_at.is_some());
 }
 
+#[test]
+fn assistant_reasoning_round_trips_separately_from_visible_content() {
+    let dir = tempfile::tempdir().unwrap();
+    let workspace = dir.path();
+    record_session_start(
+        workspace,
+        "reasoning-session",
+        "agent",
+        "Agent",
+        "reasoning-session",
+        None,
+        None,
+        None,
+        Some("reasoning-model"),
+        None,
+    )
+    .unwrap();
+
+    record_message_with_reasoning(
+        workspace,
+        "reasoning-session",
+        "assistant",
+        "I will inspect the repository.",
+        Some("First identify the relevant files."),
+        Some("reasoning-model"),
+        None,
+        None,
+        None,
+    )
+    .unwrap();
+
+    let messages = list_messages(workspace, "reasoning-session", None).unwrap();
+    assert_eq!(messages.len(), 1);
+    assert_eq!(messages[0].content, "I will inspect the repository.");
+    assert_eq!(
+        messages[0].reasoning_content.as_deref(),
+        Some("First identify the relevant files.")
+    );
+}
+
 #[test]
 fn public_listing_filters_and_caps_results() {
     let dir = tempfile::tempdir().unwrap();

crates/tinyagents-session/src/types.rs

@@ -57,6 +57,10 @@ pub struct SessionMessage {
     pub session_id: String,
     pub role: String,
     pub content: String,
+    /// Hidden model reasoning, when the provider exposed it. Kept separate
+    /// from visible `content` so search/UI consumers never mistake it for an
+    /// assistant reply.
+    pub reasoning_content: Option<String>,
     pub model: Option<String>,
     pub input_tokens: Option<u64>,
     pub output_tokens: Option<u64>,