feat: Allow resuming previous AI sessions (#3407)

This PR introduces session continuation to Atuin AI.

* Conversations with Atuin AI are stored in a local SQLite database
* Upon startup, Atuin AI tries to find a session to resume based on its
directory/workspace and the time since the last event
* If found, Atuin AI will show a note that the session has been resumed,
and an event is added to help the LLM know where the invocation
boundaries are
* If not, Atuin AI will create a new conversation
* The user can create a new conversation with `/new`
* The new setting `ai.session_continue_minutes`, which defaults to `60`,
controls how old the last event in a session can be before it's no
longer considered for automatic resuming.

<img width="1055" height="593" alt="image"
src="https://github.com/user-attachments/assets/3f9ff01a-ef64-44a9-b0e2-3a4252c5746f"
/>

## Architecture

A new `SessionService` trait defines an API contract for a service that
can manage session data. `LocalSessionService` implements this, with
`DaemonSessionService` a possible future extension point.

`SessionManager` owns a `dyn SessionService` and delegates as
appropriate.

1 files changed, 9 insertions, 0 deletions

diff --git a/crates/atuin-client/src/settings.rs b/crates/atuin-client/src/settings.rs
index 25c3bd65..9a2b84f5 100644
--- a/crates/atuin-client/src/settings.rs
+++ b/crates/atuin-client/src/settings.rs
@@ -664,6 +664,12 @@ pub struct Ai {
     /// Only necessary for custom AI endpoints.
     pub api_token: Option<String>,
 
+    /// Path to the AI sessions database.
+    pub db_path: String,
+
+    /// The maximum time in minutes that an AI session can be automatically resumed.
+    pub session_continue_minutes: i64,
+
     /// Deprecated: use opening.send_cwd instead. Kept for backwards compatibility.
     #[serde(default)]
     pub send_cwd: Option<bool>,
@@ -1467,6 +1473,7 @@ impl Settings {
         let record_store_path = data_dir.join("records.db");
         let kv_path = data_dir.join("kv.db");
         let scripts_path = data_dir.join("scripts.db");
+        let ai_sessions_path = data_dir.join("ai_sessions.db");
         let socket_path = atuin_common::utils::runtime_dir().join("atuin.sock");
         let pidfile_path = data_dir.join("atuin-daemon.pid");
         let logs_dir = atuin_common::utils::logs_dir();
@@ -1550,6 +1557,8 @@ impl Settings {
             .set_default("search.frequency_score_multiplier", 1.0)?
             .set_default("search.frecency_score_multiplier", 1.0)?
             .set_default("meta.db_path", meta_path.to_str())?
+            .set_default("ai.db_path", ai_sessions_path.to_str())?
+            .set_default("ai.session_continue_minutes", 60)?
             .set_default("ai.send_cwd", false)?
             .set_default("ai.opening.send_cwd", false)?
             .set_default("ai.opening.send_last_command", false)?