P3.1: Add TaskStore trait + SQLite backend (tables 1-7)

Define the TaskStore trait in miroir-core with SQLite backend for the
seven always-present tables from plan §4: tasks, node_settings_version,
aliases, sessions, idempotency_cache, jobs, leader_lease.

Key design choices:
- serde_json Value columns for tasks.node_tasks and aliases JSON fields
- BLOB (32 raw bytes) for idempotency_cache.body_sha256
- CAS operations for job claims and leader lease acquisition
- Idempotent migrations via schema_versions table with version gating
- WAL mode + busy_timeout=5000 for concurrent write safety
- Mutex<Connection> for thread-safe single-process access

15 tests covering CRUD round-trips, alias flipping with history
retention, session/idempotency expiry, job claim/renew, leader lease
acquire/renew/steal, migration idempotency, WAL mode, and concurrent
writes without deadlock.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

crates/miroir-core/src/task_store/mod.rs

@@ -0,0 +1,246 @@
+mod sqlite;
+
+pub use sqlite::SqliteTaskStore;
+
+use crate::Result;
+use std::collections::HashMap;
+
+/// Per-table store operations covering tables 1–7 from plan §4.
+pub trait TaskStore: Send + Sync {
+    // --- Lifecycle ---
+
+    /// Run idempotent migrations for all tables. Safe to call on every startup.
+    fn migrate(&self) -> Result<()>;
+
+    // --- Table 1: tasks ---
+
+    /// Insert a new task row.
+    fn insert_task(&self, task: &NewTask) -> Result<()>;
+
+    /// Get a task by miroir_id.
+    fn get_task(&self, miroir_id: &str) -> Result<Option<TaskRow>>;
+
+    /// Update a task's status.
+    fn update_task_status(&self, miroir_id: &str, status: &str) -> Result<bool>;
+
+    /// Update a node task within a task's node_tasks JSON.
+    fn update_node_task(&self, miroir_id: &str, node_id: &str, task_uid: u64) -> Result<bool>;
+
+    /// Set the error field on a task.
+    fn set_task_error(&self, miroir_id: &str, error: &str) -> Result<bool>;
+
+    /// List tasks with optional status filter and pagination.
+    fn list_tasks(&self, filter: &TaskFilter) -> Result<Vec<TaskRow>>;
+
+    // --- Table 2: node_settings_version ---
+
+    /// Upsert a settings version for (index_uid, node_id).
+    fn upsert_node_settings_version(
+        &self,
+        index_uid: &str,
+        node_id: &str,
+        version: i64,
+        updated_at: i64,
+    ) -> Result<()>;
+
+    /// Get the settings version for (index_uid, node_id).
+    fn get_node_settings_version(
+        &self,
+        index_uid: &str,
+        node_id: &str,
+    ) -> Result<Option<NodeSettingsVersionRow>>;
+
+    // --- Table 3: aliases ---
+
+    /// Create a new alias.
+    fn create_alias(&self, alias: &NewAlias) -> Result<()>;
+
+    /// Get an alias by name.
+    fn get_alias(&self, name: &str) -> Result<Option<AliasRow>>;
+
+    /// Flip a single alias to a new current_uid, recording history.
+    fn flip_alias(&self, name: &str, new_uid: &str, history_retention: usize) -> Result<bool>;
+
+    /// Delete an alias.
+    fn delete_alias(&self, name: &str) -> Result<bool>;
+
+    // --- Table 4: sessions ---
+
+    /// Create or replace a session.
+    fn upsert_session(&self, session: &SessionRow) -> Result<()>;
+
+    /// Get a session by id.
+    fn get_session(&self, session_id: &str) -> Result<Option<SessionRow>>;
+
+    /// Delete expired sessions.
+    fn delete_expired_sessions(&self, now_ms: i64) -> Result<usize>;
+
+    // --- Table 5: idempotency_cache ---
+
+    /// Insert an idempotency cache entry.
+    fn insert_idempotency_entry(&self, entry: &IdempotencyEntry) -> Result<()>;
+
+    /// Look up an idempotency entry by key.
+    fn get_idempotency_entry(&self, key: &str) -> Result<Option<IdempotencyEntry>>;
+
+    /// Delete expired entries.
+    fn delete_expired_idempotency_entries(&self, now_ms: i64) -> Result<usize>;
+
+    // --- Table 6: jobs ---
+
+    /// Insert a new job.
+    fn insert_job(&self, job: &NewJob) -> Result<()>;
+
+    /// Get a job by id.
+    fn get_job(&self, id: &str) -> Result<Option<JobRow>>;
+
+    /// Claim a queued job (CAS: only if still queued).
+    fn claim_job(&self, id: &str, claimed_by: &str, claim_expires_at: i64) -> Result<bool>;
+
+    /// Update job state and progress.
+    fn update_job_progress(&self, id: &str, state: &str, progress: &str) -> Result<bool>;
+
+    /// Renew a job claim (heartbeat).
+    fn renew_job_claim(&self, id: &str, claim_expires_at: i64) -> Result<bool>;
+
+    /// List jobs by state.
+    fn list_jobs_by_state(&self, state: &str) -> Result<Vec<JobRow>>;
+
+    // --- Table 7: leader_lease ---
+
+    /// Try to acquire a leader lease (CAS: only if expired or held by us).
+    /// `now_ms` is the current time for expiry comparison.
+    fn try_acquire_leader_lease(
+        &self,
+        scope: &str,
+        holder: &str,
+        expires_at: i64,
+        now_ms: i64,
+    ) -> Result<bool>;
+
+    /// Renew a leader lease we already hold.
+    fn renew_leader_lease(&self, scope: &str, holder: &str, expires_at: i64) -> Result<bool>;
+
+    /// Get current lease holder for a scope.
+    fn get_leader_lease(&self, scope: &str) -> Result<Option<LeaderLeaseRow>>;
+}
+
+// --- Row types ---
+
+/// New task to insert (table 1).
+#[derive(Debug, Clone)]
+pub struct NewTask {
+    pub miroir_id: String,
+    pub created_at: i64,
+    pub status: String,
+    pub node_tasks: HashMap<String, u64>,
+    pub error: Option<String>,
+}
+
+/// Task row from the DB (table 1).
+#[derive(Debug, Clone)]
+pub struct TaskRow {
+    pub miroir_id: String,
+    pub created_at: i64,
+    pub status: String,
+    pub node_tasks: HashMap<String, u64>,
+    pub error: Option<String>,
+}
+
+/// Node settings version row (table 2).
+#[derive(Debug, Clone)]
+pub struct NodeSettingsVersionRow {
+    pub index_uid: String,
+    pub node_id: String,
+    pub version: i64,
+    pub updated_at: i64,
+}
+
+/// New alias to create (table 3).
+#[derive(Debug, Clone)]
+pub struct NewAlias {
+    pub name: String,
+    pub kind: String,
+    pub current_uid: Option<String>,
+    pub target_uids: Option<Vec<String>>,
+    pub version: i64,
+    pub created_at: i64,
+    pub history: Vec<AliasHistoryEntry>,
+}
+
+/// Alias row from the DB (table 3).
+#[derive(Debug, Clone)]
+pub struct AliasRow {
+    pub name: String,
+    pub kind: String,
+    pub current_uid: Option<String>,
+    pub target_uids: Option<Vec<String>>,
+    pub version: i64,
+    pub created_at: i64,
+    pub history: Vec<AliasHistoryEntry>,
+}
+
+/// A single entry in alias history.
+#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
+pub struct AliasHistoryEntry {
+    pub uid: String,
+    pub flipped_at: i64,
+}
+
+/// Session row (table 4).
+#[derive(Debug, Clone)]
+pub struct SessionRow {
+    pub session_id: String,
+    pub last_write_mtask_id: Option<String>,
+    pub last_write_at: Option<i64>,
+    pub pinned_group: Option<i64>,
+    pub min_settings_version: i64,
+    pub ttl: i64,
+}
+
+/// Idempotency cache entry (table 5).
+#[derive(Debug, Clone)]
+pub struct IdempotencyEntry {
+    pub key: String,
+    pub body_sha256: Vec<u8>,
+    pub miroir_task_id: String,
+    pub expires_at: i64,
+}
+
+/// New job to insert (table 6).
+#[derive(Debug, Clone)]
+pub struct NewJob {
+    pub id: String,
+    pub type_: String,
+    pub params: String,
+    pub state: String,
+    pub progress: String,
+}
+
+/// Job row from the DB (table 6).
+#[derive(Debug, Clone)]
+pub struct JobRow {
+    pub id: String,
+    pub type_: String,
+    pub params: String,
+    pub state: String,
+    pub claimed_by: Option<String>,
+    pub claim_expires_at: Option<i64>,
+    pub progress: String,
+}
+
+/// Leader lease row (table 7).
+#[derive(Debug, Clone)]
+pub struct LeaderLeaseRow {
+    pub scope: String,
+    pub holder: String,
+    pub expires_at: i64,
+}
+
+/// Filter for listing tasks.
+#[derive(Debug, Clone, Default)]
+pub struct TaskFilter {
+    pub status: Option<String>,
+    pub limit: Option<usize>,
+    pub offset: Option<usize>,
+}