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, 1 deletions

diff --git a/crates/atuin-ai/src/stream.rs b/crates/atuin-ai/src/stream.rs
index 9c21fc05..f4f4d704 100644
--- a/crates/atuin-ai/src/stream.rs
+++ b/crates/atuin-ai/src/stream.rs
@@ -12,6 +12,7 @@ use eye_declare::Handle;
 use eyre::{Context, Result};
 use futures::StreamExt;
 use reqwest::Url;
+use reqwest::header::USER_AGENT;
 
 use crate::{
     context::{AppContext, ClientContext},
@@ -19,6 +20,8 @@ use crate::{
     tui::{Session, events::AiTuiEvent},
 };
 
+static APP_USER_AGENT: &str = concat!("atuin/", env!("CARGO_PKG_VERSION"));
+
 /// Frames that alter the stream lifecycle — terminal or state-changing.
 #[derive(Debug, Clone)]
 pub(crate) enum StreamControl {
@@ -57,6 +60,7 @@ pub(crate) struct ChatRequest {
     pub messages: Vec<serde_json::Value>,
     pub session_id: Option<String>,
     pub capabilities: Vec<String>,
+    pub invocation_id: String,
 }
 
 impl ChatRequest {
@@ -64,8 +68,9 @@ impl ChatRequest {
         messages: Vec<serde_json::Value>,
         session_id: Option<String>,
         capabilities: &AiCapabilities,
+        invocation_id: String,
     ) -> Self {
-        let mut caps = vec![];
+        let mut caps = vec!["client_invocations".to_string()];
         if capabilities.enable_history_search.unwrap_or(true) {
             caps.push("client_v1_atuin_history".to_string());
         }
@@ -82,6 +87,7 @@ impl ChatRequest {
             messages,
             session_id,
             capabilities: caps,
+            invocation_id,
         }
     }
 }
@@ -112,6 +118,7 @@ fn create_chat_stream(
             "messages": request.messages,
             "context": context,
             "capabilities": request.capabilities,
+            "invocation_id": request.invocation_id
         });
 
         if let Some(ref sid) = request.session_id {
@@ -123,6 +130,7 @@ fn create_chat_stream(
         let response = match client
             .post(endpoint.clone())
             .header("Accept", "text/event-stream")
+            .header(USER_AGENT, APP_USER_AGENT)
             .bearer_auth(&token)
             .json(&request_body)
             .send()