feat(persona-chat): practice mode — play the contact

An anchored conversation now has a mode. 'about' is the existing behaviour (a
persona talks with the user about the thread). 'as_contact' has the model play
the contact so the user can rehearse the conversation: its own prompt (stay in
the contact's voice, don't invent facts, coach on 'out of character'), no
persona prompt, and only the thread tools — no memory, library, calendar or
other-thread access, and no knowledge writes.

The shared persona/file-chat loop now refuses tool calls that weren't in the
turn's catalog, so the gates hold even when a model names a tool it wasn't
offered.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/database/persona_dao.rs

@@ -47,6 +47,37 @@ pub struct SmsAnchor {
     /// Unix seconds of the anchor message.
     pub timestamp: i64,
     pub context: String,
+    pub mode: AnchorMode,
+}
+
+/// How an anchored conversation relates to its SMS thread.
+#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum AnchorMode {
+    /// A persona talks with the user about the thread.
+    #[default]
+    About,
+    /// The model plays the contact so the user can practise the
+    /// conversation.
+    AsContact,
+}
+
+impl AnchorMode {
+    pub fn as_str(self) -> &'static str {
+        match self {
+            AnchorMode::About => "about",
+            AnchorMode::AsContact => "as_contact",
+        }
+    }
+
+    /// Stored value → mode. NULL and anything unrecognised read as `About`,
+    /// the behaviour rows had before the column existed.
+    pub fn from_column(value: Option<&str>) -> Self {
+        match value {
+            Some("as_contact") => AnchorMode::AsContact,
+            _ => AnchorMode::About,
+        }
+    }
 }
 
 /// The column tuple every persona-chat read selects. Shared by the
@@ -65,6 +96,7 @@ type PersonaChatColumns = (
     Option<i64>,
     Option<i64>,
     Option<String>,
+    Option<String>,
 );
 
 macro_rules! persona_chat_select {
@@ -82,6 +114,7 @@ macro_rules! persona_chat_select {
             anchor_message_id,
             anchor_ts,
             anchor_context,
+            anchor_mode,
         )
     };
 }
@@ -101,6 +134,7 @@ fn persona_chat_row(
         anchor_message_id,
         anchor_ts,
         anchor_context,
+        anchor_mode,
     ): PersonaChatColumns,
 ) -> PersonaChatRow {
     // An anchor needs at least the thread and the message; the rest has a
@@ -112,6 +146,7 @@ fn persona_chat_row(
             message_id,
             timestamp: anchor_ts.unwrap_or(0),
             context: anchor_context.unwrap_or_default(),
+            mode: AnchorMode::from_column(anchor_mode.as_deref()),
         }),
         _ => None,
     };
@@ -545,6 +580,7 @@ impl PersonaDao for SqlitePersonaDao {
                     anchor_message_id.eq(Some(anchor.message_id)),
                     anchor_ts.eq(Some(anchor.timestamp)),
                     anchor_context.eq(Some(&anchor.context)),
+                    anchor_mode.eq(Some(anchor.mode.as_str())),
                 ))
                 .execute(conn.deref_mut())
                 .map_err(|e| anyhow::anyhow!("Insert error: {}", e))?;
@@ -876,6 +912,7 @@ mod tests {
             message_id: 9001,
             timestamp: 1_700_000_000,
             context: "[2023-11-14 22:13] Sam: see you there".to_string(),
+            mode: AnchorMode::AsContact,
         };
         let anchored = dao
             .create_anchored_persona_chat(uid, "journal", 100, &anchor)
@@ -895,6 +932,17 @@ mod tests {
         );
     }
 
+    #[test]
+    fn anchor_mode_reads_null_and_unknown_as_about() {
+        assert_eq!(AnchorMode::from_column(None), AnchorMode::About);
+        assert_eq!(AnchorMode::from_column(Some("weird")), AnchorMode::About);
+        assert_eq!(AnchorMode::from_column(Some("about")), AnchorMode::About);
+        assert_eq!(
+            AnchorMode::from_column(Some(AnchorMode::AsContact.as_str())),
+            AnchorMode::AsContact
+        );
+    }
+
     #[test]
     fn persona_chat_list_is_empty_for_a_user_who_has_never_chatted() {
         let (mut dao, uid) = dao_with_user("p8");