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, 49 insertions, 0 deletions

diff --git a/crates/atuin-ai/src/tui/components/session_continue.rs b/crates/atuin-ai/src/tui/components/session_continue.rs
new file mode 100644
index 00000000..bfbfb191
--- /dev/null
+++ b/crates/atuin-ai/src/tui/components/session_continue.rs
@@ -0,0 +1,49 @@
+use chrono_humanize::HumanTime;
+use eye_declare::{Elements, Hooks, Span, Text, component, element, props};
+use ratatui::style::{Color, Modifier, Style};
+
+#[props]
+pub(crate) struct SessionContinue {
+    pub continued_at: Option<chrono::DateTime<chrono::Utc>>,
+}
+
+#[derive(Default)]
+pub(crate) struct SessionContinueState {
+    /// Frozen on mount so the label doesn't change on every render.
+    label: Option<String>,
+}
+
+#[component(props = SessionContinue, state = SessionContinueState)]
+fn session_continue(
+    _props: &SessionContinue,
+    state: &SessionContinueState,
+    hooks: &mut Hooks<SessionContinue, SessionContinueState>,
+) -> Elements {
+    hooks.use_mount(|props, state| {
+        state.label = Some(match props.continued_at {
+            Some(t) => {
+                let human = HumanTime::from(t - chrono::Utc::now());
+                format!(
+                    "  Continuing previous session (last active {human}) - type /new to start a new session"
+                )
+            }
+            None => {
+                "  Continuing previous session - type /new to start a new session".to_string()
+            }
+        });
+    });
+
+    let resume_label = state
+        .label
+        .as_deref()
+        .unwrap_or("  Continuing previous session - type /new to start a new session");
+
+    element! {
+        Text {
+            Span(
+                text: resume_label,
+                style: Style::default().fg(Color::DarkGray).add_modifier(Modifier::ITALIC),
+            )
+        }
+    }
+}