feat: add optimistic locking for bttask and error classification

Version column in tasks table with WHERE id=? AND version=? guard.
Conflict detection in TaskBoardTab. error-classifier.ts: 6 error types
with actionable messages and retry logic. UsageMeter.svelte.

bttask

@@ -98,6 +98,7 @@ def init_db():
             sort_order INTEGER DEFAULT 0,
             created_at TEXT DEFAULT (datetime('now')),
             updated_at TEXT DEFAULT (datetime('now')),
+            version INTEGER DEFAULT 1,
             FOREIGN KEY (assigned_to) REFERENCES agents(id),
             FOREIGN KEY (created_by) REFERENCES agents(id)
         );
@@ -117,6 +118,14 @@ def init_db():
         CREATE INDEX IF NOT EXISTS idx_tasks_assigned ON tasks(assigned_to);
         CREATE INDEX IF NOT EXISTS idx_task_comments_task ON task_comments(task_id);
     """)
+
+    # Migration: add version column if missing (for existing databases)
+    cursor = db.execute("PRAGMA table_info(tasks)")
+    columns = [row[1] for row in cursor.fetchall()]
+    if 'version' not in columns:
+        db.execute("ALTER TABLE tasks ADD COLUMN version INTEGER DEFAULT 1")
+        db.commit()
+
     db.commit()
     db.close()
 
@@ -414,11 +423,20 @@ def cmd_status(args):
         return
 
     old_status = task['status']
-    db.execute(
-        "UPDATE tasks SET status = ?, updated_at = datetime('now') WHERE id = ?",
-        (new_status, task['id'])
+    current_version = task['version'] if task['version'] is not None else 1
+
+    cursor = db.execute(
+        "UPDATE tasks SET status = ?, version = version + 1, updated_at = datetime('now') "
+        "WHERE id = ? AND version = ?",
+        (new_status, task['id'], current_version)
     )
 
+    if cursor.rowcount == 0:
+        print(f"{C_RED}Error: Task was modified by another agent (version conflict).{C_RESET}")
+        print(f"{C_DIM}Re-fetch the task and try again.{C_RESET}")
+        db.close()
+        sys.exit(1)
+
     # Auto-add comment for status change
     comment_id = str(uuid.uuid4())
     db.execute(
@@ -429,7 +447,8 @@ def cmd_status(args):
     db.commit()
     db.close()
 
-    print(f"{C_GREEN}✓ [{short_id(task['id'])}] {format_state(old_status)} → {format_state(new_status)}{C_RESET}")
+    new_version = current_version + 1
+    print(f"{C_GREEN}✓ [{short_id(task['id'])}] {format_state(old_status)} → {format_state(new_status)} {C_DIM}(v{new_version}){C_RESET}")
 
 
 def cmd_comment(args):

v2/src-tauri/src/bttask.rs

@@ -31,10 +31,24 @@ fn open_db() -> Result<Connection, String> {
     }
     let conn = Connection::open_with_flags(&path, OpenFlags::SQLITE_OPEN_READ_WRITE)
         .map_err(|e| format!("Failed to open btmsg.db: {e}"))?;
-    conn.pragma_update(None, "journal_mode", "WAL")
+    conn.query_row("PRAGMA journal_mode=WAL", [], |_| Ok(()))
         .map_err(|e| format!("Failed to set WAL mode: {e}"))?;
     conn.pragma_update(None, "busy_timeout", 5000)
         .map_err(|e| format!("Failed to set busy_timeout: {e}"))?;
+
+    // Migration: add version column if missing
+    let has_version: i64 = conn
+        .query_row(
+            "SELECT COUNT(*) FROM pragma_table_info('tasks') WHERE name='version'",
+            [],
+            |row| row.get(0),
+        )
+        .unwrap_or(0);
+    if has_version == 0 {
+        conn.execute("ALTER TABLE tasks ADD COLUMN version INTEGER DEFAULT 1", [])
+            .map_err(|e| format!("Migration (version column) failed: {e}"))?;
+    }
+
     Ok(conn)
 }
 
@@ -53,6 +67,7 @@ pub struct Task {
     pub sort_order: i32,
     pub created_at: String,
     pub updated_at: String,
+    pub version: i64,
 }
 
 #[derive(Debug, Serialize, Deserialize)]
@@ -72,7 +87,7 @@ pub fn list_tasks(group_id: &str) -> Result<Vec<Task>, String> {
         .prepare(
             "SELECT id, title, description, status, priority, assigned_to,
                     created_by, group_id, parent_task_id, sort_order,
-                    created_at, updated_at
+                    created_at, updated_at, version
              FROM tasks WHERE group_id = ?1
              ORDER BY sort_order ASC, created_at DESC",
         )
@@ -93,6 +108,7 @@ pub fn list_tasks(group_id: &str) -> Result<Vec<Task>, String> {
                 sort_order: row.get::<_, i32>("sort_order").unwrap_or(0),
                 created_at: row.get::<_, String>("created_at").unwrap_or_default(),
                 updated_at: row.get::<_, String>("updated_at").unwrap_or_default(),
+                version: row.get::<_, i64>("version").unwrap_or(1),
             })
         })
         .map_err(|e| format!("Query error: {e}"))?;
@@ -128,9 +144,11 @@ pub fn task_comments(task_id: &str) -> Result<Vec<TaskComment>, String> {
         .map_err(|e| format!("Row error: {e}"))
 }
 
-/// Update task status
-/// When transitioning to 'review', auto-posts to #review-queue channel if it exists
-pub fn update_task_status(task_id: &str, status: &str) -> Result<(), String> {
+/// Update task status with optimistic locking.
+/// `expected_version` must match the current version in the database.
+/// Returns the new version on success.
+/// When transitioning to 'review', auto-posts to #review-queue channel if it exists.
+pub fn update_task_status(task_id: &str, status: &str, expected_version: i64) -> Result<i64, String> {
     let valid = ["todo", "progress", "review", "done", "blocked"];
     if !valid.contains(&status) {
         return Err(format!("Invalid status '{}'. Valid: {:?}", status, valid));
@@ -148,18 +166,25 @@ pub fn update_task_status(task_id: &str, status: &str) -> Result<(), String> {
         None
     };
 
-    db.execute(
-        "UPDATE tasks SET status = ?1, updated_at = datetime('now') WHERE id = ?2",
-        params![status, task_id],
+    let rows_affected = db.execute(
+        "UPDATE tasks SET status = ?1, version = version + 1, updated_at = datetime('now')
+         WHERE id = ?2 AND version = ?3",
+        params![status, task_id, expected_version],
     )
     .map_err(|e| format!("Update error: {e}"))?;
 
+    if rows_affected == 0 {
+        return Err("Task was modified by another agent (version conflict)".into());
+    }
+
+    let new_version = expected_version + 1;
+
     // Auto-post to #review-queue channel on review transition
     if let Some((title, group_id)) = task_title {
         notify_review_channel(&db, &group_id, task_id, &title);
     }
 
-    Ok(())
+    Ok(new_version)
 }
 
 /// Post a notification to #review-queue channel (best-effort, never fails the parent operation)
@@ -295,7 +320,8 @@ mod tests {
                 parent_task_id TEXT,
                 sort_order INTEGER DEFAULT 0,
                 created_at TEXT DEFAULT (datetime('now')),
-                updated_at TEXT DEFAULT (datetime('now'))
+                updated_at TEXT DEFAULT (datetime('now')),
+                version INTEGER DEFAULT 1
             );
             CREATE TABLE task_comments (
                 id TEXT PRIMARY KEY,
@@ -342,7 +368,7 @@ mod tests {
         let mut stmt = conn.prepare(
             "SELECT id, title, description, status, priority, assigned_to,
                     created_by, group_id, parent_task_id, sort_order,
-                    created_at, updated_at
+                    created_at, updated_at, version
              FROM tasks WHERE group_id = ?1
              ORDER BY sort_order ASC, created_at DESC",
         ).unwrap();
@@ -361,6 +387,7 @@ mod tests {
                 sort_order: row.get::<_, i32>("sort_order").unwrap_or(0),
                 created_at: row.get::<_, String>("created_at").unwrap_or_default(),
                 updated_at: row.get::<_, String>("updated_at").unwrap_or_default(),
+                version: row.get::<_, i64>("version").unwrap_or(1),
             })
         }).unwrap().collect::<Result<Vec<_>, _>>().unwrap();
 
@@ -434,6 +461,7 @@ mod tests {
             sort_order: 0,
             created_at: "2026-01-01".into(),
             updated_at: "2026-01-01".into(),
+            version: 1,
         };
 
         let json = serde_json::to_value(&task).unwrap();
@@ -606,4 +634,133 @@ mod tests {
             .unwrap();
         assert_eq!(count_g2, 1, "should count only review tasks in g2");
     }
+
+    // ---- Optimistic locking (version column) ----
+
+    #[test]
+    fn test_version_column_defaults_to_1() {
+        let conn = test_db();
+        conn.execute(
+            "INSERT INTO tasks (id, title, created_by, group_id) VALUES ('t1', 'Test', 'admin', 'g1')",
+            [],
+        ).unwrap();
+
+        let version: i64 = conn
+            .query_row("SELECT version FROM tasks WHERE id = 't1'", [], |row| row.get(0))
+            .unwrap();
+        assert_eq!(version, 1);
+    }
+
+    #[test]
+    fn test_optimistic_lock_success() {
+        let conn = test_db();
+        conn.execute(
+            "INSERT INTO tasks (id, title, status, created_by, group_id) VALUES ('t1', 'Test', 'todo', 'admin', 'g1')",
+            [],
+        ).unwrap();
+
+        // Update with correct version (1)
+        let rows = conn.execute(
+            "UPDATE tasks SET status = 'progress', version = version + 1, updated_at = datetime('now')
+             WHERE id = 't1' AND version = 1",
+            [],
+        ).unwrap();
+        assert_eq!(rows, 1, "should affect 1 row");
+
+        let new_version: i64 = conn
+            .query_row("SELECT version FROM tasks WHERE id = 't1'", [], |row| row.get(0))
+            .unwrap();
+        assert_eq!(new_version, 2);
+    }
+
+    #[test]
+    fn test_optimistic_lock_conflict() {
+        let conn = test_db();
+        conn.execute(
+            "INSERT INTO tasks (id, title, status, created_by, group_id) VALUES ('t1', 'Test', 'todo', 'admin', 'g1')",
+            [],
+        ).unwrap();
+
+        // First update succeeds
+        conn.execute(
+            "UPDATE tasks SET status = 'progress', version = version + 1, updated_at = datetime('now')
+             WHERE id = 't1' AND version = 1",
+            [],
+        ).unwrap();
+
+        // Second update with stale version (1) should affect 0 rows
+        let rows = conn.execute(
+            "UPDATE tasks SET status = 'review', version = version + 1, updated_at = datetime('now')
+             WHERE id = 't1' AND version = 1",
+            [],
+        ).unwrap();
+        assert_eq!(rows, 0, "stale version should affect 0 rows");
+
+        // Task should still be in 'progress' state
+        let status: String = conn
+            .query_row("SELECT status FROM tasks WHERE id = 't1'", [], |row| row.get(0))
+            .unwrap();
+        assert_eq!(status, "progress");
+    }
+
+    #[test]
+    fn test_version_in_list_tasks_query() {
+        let conn = test_db();
+        conn.execute(
+            "INSERT INTO tasks (id, title, created_by, group_id, sort_order) VALUES ('t1', 'V1', 'admin', 'g1', 1)",
+            [],
+        ).unwrap();
+        // Bump version to 3
+        conn.execute("UPDATE tasks SET version = 3 WHERE id = 't1'", []).unwrap();
+
+        let mut stmt = conn.prepare(
+            "SELECT id, title, description, status, priority, assigned_to,
+                    created_by, group_id, parent_task_id, sort_order,
+                    created_at, updated_at, version
+             FROM tasks WHERE group_id = ?1",
+        ).unwrap();
+
+        let tasks: Vec<Task> = stmt.query_map(params!["g1"], |row| {
+            Ok(Task {
+                id: row.get("id")?,
+                title: row.get("title")?,
+                description: row.get::<_, String>("description").unwrap_or_default(),
+                status: row.get::<_, String>("status").unwrap_or_else(|_| "todo".into()),
+                priority: row.get::<_, String>("priority").unwrap_or_else(|_| "medium".into()),
+                assigned_to: row.get("assigned_to")?,
+                created_by: row.get("created_by")?,
+                group_id: row.get("group_id")?,
+                parent_task_id: row.get("parent_task_id")?,
+                sort_order: row.get::<_, i32>("sort_order").unwrap_or(0),
+                created_at: row.get::<_, String>("created_at").unwrap_or_default(),
+                updated_at: row.get::<_, String>("updated_at").unwrap_or_default(),
+                version: row.get::<_, i64>("version").unwrap_or(1),
+            })
+        }).unwrap().collect::<Result<Vec<_>, _>>().unwrap();
+
+        assert_eq!(tasks.len(), 1);
+        assert_eq!(tasks[0].version, 3);
+    }
+
+    #[test]
+    fn test_version_serializes_to_camel_case() {
+        let task = Task {
+            id: "t1".into(),
+            title: "Test".into(),
+            description: "".into(),
+            status: "todo".into(),
+            priority: "medium".into(),
+            assigned_to: None,
+            created_by: "admin".into(),
+            group_id: "g1".into(),
+            parent_task_id: None,
+            sort_order: 0,
+            created_at: "2026-01-01".into(),
+            updated_at: "2026-01-01".into(),
+            version: 5,
+        };
+
+        let json = serde_json::to_value(&task).unwrap();
+        assert_eq!(json.get("version").unwrap(), 5);
+    }
 }

v2/src-tauri/src/commands/bttask.rs

@@ -11,8 +11,8 @@ pub fn bttask_comments(task_id: String) -> Result<Vec<bttask::TaskComment>, Stri
 }
 
 #[tauri::command]
-pub fn bttask_update_status(task_id: String, status: String) -> Result<(), String> {
-    bttask::update_task_status(&task_id, &status)
+pub fn bttask_update_status(task_id: String, status: String, version: i64) -> Result<i64, String> {
+    bttask::update_task_status(&task_id, &status, version)
 }
 
 #[tauri::command]

v2/src/lib/adapters/bttask-bridge.ts

@@ -16,6 +16,7 @@ export interface Task {
   sortOrder: number;
   createdAt: string;
   updatedAt: string;
+  version: number;
 }
 
 export interface TaskComment {
@@ -34,8 +35,9 @@ export async function getTaskComments(taskId: string): Promise<TaskComment[]> {
   return invoke<TaskComment[]>('bttask_comments', { taskId });
 }
 
-export async function updateTaskStatus(taskId: string, status: string): Promise<void> {
-  return invoke('bttask_update_status', { taskId, status });
+/** Update task status with optimistic locking. Returns the new version number. */
+export async function updateTaskStatus(taskId: string, status: string, version: number): Promise<number> {
+  return invoke<number>('bttask_update_status', { taskId, status, version });
 }
 
 export async function addTaskComment(taskId: string, agentId: AgentId, content: string): Promise<string> {

v2/src/lib/components/Agent/AgentPane.svelte

@@ -16,6 +16,8 @@
   import type { SessionAnchor } from '../../types/anchors';
 
   import AgentTree from './AgentTree.svelte';
+  import UsageMeter from './UsageMeter.svelte';
+  import { notify } from '../../stores/notifications.svelte';
   import { getHighlighter, highlightCode, escapeHtml } from '../../utils/highlight';
   import type {
     TextContent,
@@ -373,6 +375,35 @@
     if (totalTokens === 0) return 0;
     return Math.min(100, Math.round((totalTokens / DEFAULT_CONTEXT_LIMIT) * 100));
   });
+
+  // Context meter color class based on thresholds
+  let contextColorClass = $derived.by(() => {
+    if (contextPercent >= 90) return 'context-critical';
+    if (contextPercent >= 75) return 'context-high';
+    if (contextPercent >= 50) return 'context-medium';
+    return '';
+  });
+
+  // Session burn rate ($/hr)
+  let burnRatePerHr = $derived.by(() => {
+    if (!session || session.durationMs <= 0 || session.costUsd <= 0) return 0;
+    return (session.costUsd / session.durationMs) * 3_600_000;
+  });
+
+  // 90% context warning (fire once per session)
+  let contextWarningFired = $state(false);
+  $effect(() => {
+    if (contextPercent >= 90 && !contextWarningFired && session?.status === 'running') {
+      contextWarningFired = true;
+      notify('warning', `Context usage at ${contextPercent}% — approaching model limit`);
+    }
+  });
+  // Reset warning tracker when session changes
+  $effect(() => {
+    if (session?.id) {
+      contextWarningFired = false;
+    }
+  });
 </script>
 
 <div class="agent-pane" data-testid="agent-pane" data-agent-status={session?.status ?? 'idle'}>
@@ -538,12 +569,17 @@
         <div class="running-indicator">
           <span class="pulse"></span>
           <span>Running...</span>
-          {#if contextPercent > 0}
-            <span class="context-meter" title="Context window usage">
-              <span class="context-fill" class:context-streaming={isRunning} style="width: {contextPercent}%"></span>
+          {#if capabilities.supportsCost && (session.inputTokens > 0 || session.outputTokens > 0)}
+            <UsageMeter inputTokens={session.inputTokens} outputTokens={session.outputTokens} contextLimit={DEFAULT_CONTEXT_LIMIT} />
+          {:else if contextPercent > 0}
+            <span class="context-meter {contextColorClass}" title="Context window usage">
+              <span class="context-fill context-streaming" style="width: {contextPercent}%"></span>
               <span class="context-label">{contextPercent}%</span>
             </span>
           {/if}
+          {#if burnRatePerHr > 0}
+            <span class="burn-rate" title="Current session burn rate">${burnRatePerHr.toFixed(2)}/hr</span>
+          {/if}
           {#if !autoScroll}
             <button class="scroll-btn" onclick={() => { autoScroll = true; scrollContainer?.querySelector('#message-end')?.scrollIntoView({ behavior: 'instant' as ScrollBehavior }); }}>↓ Bottom</button>
           {/if}
@@ -555,14 +591,17 @@
           {#if totalCost && totalCost.costUsd > session.costUsd}
             <span class="total-cost">(total: ${totalCost.costUsd.toFixed(4)})</span>
           {/if}
-          <span class="cost-detail">{session.inputTokens + session.outputTokens} tok</span>
-          <span class="cost-detail">{(session.durationMs / 1000).toFixed(1)}s</span>
-          {#if contextPercent > 0}
-            <span class="context-meter" title="Context window usage">
-              <span class="context-fill" style="width: {contextPercent}%"></span>
-              <span class="context-label">{contextPercent}%</span>
-            </span>
+          {#if capabilities.supportsCost}
+            <span class="cost-detail token-in" title="Input tokens">{session.inputTokens.toLocaleString()} in</span>
+            <span class="cost-detail token-out" title="Output tokens">{session.outputTokens.toLocaleString()} out</span>
+          {:else}
+            <span class="cost-detail">{session.inputTokens + session.outputTokens} tok</span>
           {/if}
+          <span class="cost-detail">{(session.durationMs / 1000).toFixed(1)}s</span>
+          {#if burnRatePerHr > 0}
+            <span class="burn-rate" title="Session average burn rate">${burnRatePerHr.toFixed(2)}/hr</span>
+          {/if}
+          <UsageMeter inputTokens={session.inputTokens} outputTokens={session.outputTokens} contextLimit={DEFAULT_CONTEXT_LIMIT} />
           {#if !autoScroll}
             <button class="scroll-btn" onclick={() => { autoScroll = true; scrollContainer?.querySelector('#message-end')?.scrollIntoView({ behavior: 'instant' as ScrollBehavior }); }}>↓ Bottom</button>
           {/if}
@@ -1333,6 +1372,21 @@
   .total-cost { color: var(--ctp-overlay1); font-size: 0.6875rem; }
   .error-bar { color: var(--ctp-red); }
 
+  .burn-rate {
+    font-size: 0.625rem;
+    font-family: var(--term-font-family, monospace);
+    color: var(--ctp-peach);
+    white-space: nowrap;
+  }
+
+  .token-in { color: var(--ctp-blue); }
+  .token-out { color: var(--ctp-green); }
+
+  /* Context meter threshold colors */
+  .context-medium .context-fill { background: var(--ctp-yellow); }
+  .context-high .context-fill { background: var(--ctp-peach); }
+  .context-critical .context-fill { background: var(--ctp-red); }
+
   /* === Session controls === */
   .session-controls {
     display: flex;

v2/src/lib/components/Agent/UsageMeter.svelte

@@ -0,0 +1,146 @@
+<script lang="ts">
+  interface Props {
+    inputTokens: number;
+    outputTokens: number;
+    contextLimit?: number;
+  }
+
+  let { inputTokens, outputTokens, contextLimit = 200_000 }: Props = $props();
+
+  let totalTokens = $derived(inputTokens + outputTokens);
+  let pct = $derived(contextLimit > 0 ? Math.min((totalTokens / contextLimit) * 100, 100) : 0);
+
+  let thresholdClass = $derived.by(() => {
+    if (pct >= 90) return 'critical';
+    if (pct >= 75) return 'high';
+    if (pct >= 50) return 'medium';
+    return 'low';
+  });
+
+  function formatTokens(n: number): string {
+    if (n >= 1_000_000) return `${(n / 1_000_000).toFixed(1)}M`;
+    if (n >= 1_000) return `${(n / 1_000).toFixed(1)}k`;
+    return String(n);
+  }
+
+  let showTooltip = $state(false);
+</script>
+
+{#if totalTokens > 0}
+  <!-- svelte-ignore a11y_no_static_element_interactions -->
+  <div
+    class="usage-meter"
+    class:critical={thresholdClass === 'critical'}
+    class:high={thresholdClass === 'high'}
+    class:medium={thresholdClass === 'medium'}
+    class:low={thresholdClass === 'low'}
+    onmouseenter={() => showTooltip = true}
+    onmouseleave={() => showTooltip = false}
+  >
+    <div class="meter-track">
+      <div class="meter-fill" style="width: {pct}%"></div>
+    </div>
+    <span class="meter-label">{formatTokens(totalTokens)}</span>
+
+    {#if showTooltip}
+      <div class="meter-tooltip">
+        <div class="tooltip-row">
+          <span class="tooltip-key">Input</span>
+          <span class="tooltip-val">{formatTokens(inputTokens)}</span>
+        </div>
+        <div class="tooltip-row">
+          <span class="tooltip-key">Output</span>
+          <span class="tooltip-val">{formatTokens(outputTokens)}</span>
+        </div>
+        <div class="tooltip-row">
+          <span class="tooltip-key">Total</span>
+          <span class="tooltip-val">{formatTokens(totalTokens)}</span>
+        </div>
+        <div class="tooltip-divider"></div>
+        <div class="tooltip-row">
+          <span class="tooltip-key">Limit</span>
+          <span class="tooltip-val">{formatTokens(contextLimit)}</span>
+        </div>
+        <div class="tooltip-row">
+          <span class="tooltip-key">Used</span>
+          <span class="tooltip-val">{pct.toFixed(1)}%</span>
+        </div>
+      </div>
+    {/if}
+  </div>
+{/if}
+
+<style>
+  .usage-meter {
+    display: inline-flex;
+    align-items: center;
+    gap: 0.375rem;
+    position: relative;
+  }
+
+  .meter-track {
+    width: 3rem;
+    height: 0.375rem;
+    background: var(--ctp-surface0);
+    border-radius: 0.1875rem;
+    overflow: hidden;
+    flex-shrink: 0;
+  }
+
+  .meter-fill {
+    height: 100%;
+    border-radius: 0.1875rem;
+    transition: width 0.3s ease, background 0.3s ease;
+  }
+
+  .low .meter-fill { background: var(--ctp-green); }
+  .medium .meter-fill { background: var(--ctp-yellow); }
+  .high .meter-fill { background: var(--ctp-peach); }
+  .critical .meter-fill { background: var(--ctp-red); }
+
+  .meter-label {
+    font-size: 0.625rem;
+    font-family: var(--term-font-family, monospace);
+    color: var(--ctp-overlay1);
+    white-space: nowrap;
+  }
+
+  .meter-tooltip {
+    position: absolute;
+    bottom: calc(100% + 0.375rem);
+    left: 50%;
+    transform: translateX(-50%);
+    background: var(--ctp-surface0);
+    border: 1px solid var(--ctp-surface1);
+    border-radius: 0.25rem;
+    padding: 0.375rem 0.5rem;
+    min-width: 7.5rem;
+    z-index: 100;
+    box-shadow: 0 0.125rem 0.5rem color-mix(in srgb, var(--ctp-crust) 40%, transparent);
+  }
+
+  .tooltip-row {
+    display: flex;
+    justify-content: space-between;
+    align-items: center;
+    gap: 0.75rem;
+    padding: 0.0625rem 0;
+  }
+
+  .tooltip-key {
+    font-size: 0.625rem;
+    color: var(--ctp-overlay0);
+  }
+
+  .tooltip-val {
+    font-size: 0.625rem;
+    font-family: var(--term-font-family, monospace);
+    color: var(--ctp-text);
+  }
+
+  .tooltip-divider {
+    height: 1px;
+    background: var(--ctp-surface1);
+    margin: 0.1875rem 0;
+  }
+</style>

v2/src/lib/components/Workspace/ContextTab.svelte

@@ -262,6 +262,31 @@
     return `${m}m ${s % 60}s`;
   }
 
+  // --- Cost analytics ---
+  let avgCostPerTurn = $derived(
+    session && session.numTurns > 0
+      ? totalCost.costUsd / session.numTurns
+      : 0
+  );
+
+  let tokenEfficiency = $derived(
+    totalCost.inputTokens > 0
+      ? totalCost.outputTokens / totalCost.inputTokens
+      : 0
+  );
+
+  let burnRatePerHr = $derived.by(() => {
+    if (!session || session.durationMs <= 0 || totalCost.costUsd <= 0) return 0;
+    return (totalCost.costUsd / session.durationMs) * 3_600_000;
+  });
+
+  // Cost projection: estimate total cost if context fills to 100%
+  let costProjection = $derived.by(() => {
+    const usedPct = totalCost.inputTokens / CONTEXT_WINDOW;
+    if (usedPct <= 0) return 0;
+    return totalCost.costUsd / usedPct;
+  });
+
   function opColor(op: string): string {
     switch (op) {
       case 'read': return 'var(--ctp-blue)';
@@ -689,6 +714,39 @@
       {/if}
     </div>
 
+    <!-- Cost Analytics -->
+    {#if totalCost.costUsd > 0}
+      <div class="cost-analytics-section">
+        <div class="section-header">
+          <span class="section-title">Cost Analytics</span>
+        </div>
+        <div class="cost-grid">
+          <div class="cost-cell">
+            <span class="cost-cell-value">{formatCost(totalCost.costUsd)}</span>
+            <span class="cost-cell-label">Total Cost</span>
+          </div>
+          <div class="cost-cell">
+            <span class="cost-cell-value">{formatCost(avgCostPerTurn)}</span>
+            <span class="cost-cell-label">Avg / Turn</span>
+          </div>
+          <div class="cost-cell">
+            <span class="cost-cell-value">{tokenEfficiency.toFixed(2)}</span>
+            <span class="cost-cell-label">Out/In Ratio</span>
+          </div>
+          <div class="cost-cell">
+            <span class="cost-cell-value">${burnRatePerHr.toFixed(2)}/hr</span>
+            <span class="cost-cell-label">Burn Rate</span>
+          </div>
+          {#if costProjection > 0}
+            <div class="cost-cell projection">
+              <span class="cost-cell-value">{formatCost(costProjection)}</span>
+              <span class="cost-cell-label">Est. Full Context</span>
+            </div>
+          {/if}
+        </div>
+      </div>
+    {/if}
+
     <!-- Context Meter -->
     <div class="meter-section">
       <div class="meter-header">
@@ -1139,6 +1197,52 @@
   .compaction-pill .stat-value { color: var(--ctp-yellow); }
   .compaction-pill .stat-label { color: var(--ctp-yellow); opacity: 0.7; }
 
+  /* Cost Analytics */
+  .cost-analytics-section {
+    padding: 0.375rem 0.625rem;
+    border-bottom: 1px solid var(--ctp-surface0);
+    flex-shrink: 0;
+  }
+
+  .cost-grid {
+    display: grid;
+    grid-template-columns: repeat(auto-fill, minmax(5rem, 1fr));
+    gap: 0.375rem;
+    margin-top: 0.25rem;
+  }
+
+  .cost-cell {
+    display: flex;
+    flex-direction: column;
+    align-items: center;
+    padding: 0.375rem 0.25rem;
+    background: var(--ctp-surface0);
+    border-radius: 0.25rem;
+  }
+
+  .cost-cell-value {
+    font-size: 0.75rem;
+    font-weight: 700;
+    font-family: var(--term-font-family, monospace);
+    color: var(--ctp-text);
+  }
+
+  .cost-cell-label {
+    font-size: 0.55rem;
+    color: var(--ctp-overlay0);
+    text-transform: uppercase;
+    letter-spacing: 0.05em;
+    margin-top: 0.125rem;
+  }
+
+  .cost-cell.projection {
+    background: color-mix(in srgb, var(--ctp-peach) 10%, var(--ctp-surface0));
+  }
+
+  .cost-cell.projection .cost-cell-value {
+    color: var(--ctp-peach);
+  }
+
   /* Context meter */
   .meter-section {
     padding: 0.5rem 0.625rem;

v2/src/lib/components/Workspace/TaskBoardTab.svelte

@@ -84,10 +84,18 @@
 
   async function handleStatusChange(taskId: string, newStatus: string) {
     try {
-      await updateTaskStatus(taskId, newStatus);
+      const task = tasks.find(t => t.id === taskId);
+      const version = task?.version ?? 1;
+      await updateTaskStatus(taskId, newStatus, version);
       await loadTasks();
-    } catch (e) {
-      console.warn('Failed to update task status:', e);
+    } catch (e: any) {
+      const msg = e?.message ?? String(e);
+      if (msg.includes('version conflict')) {
+        console.warn('Version conflict on task update, reloading:', msg);
+        await loadTasks();
+      } else {
+        console.warn('Failed to update task status:', e);
+      }
     }
   }
 

v2/src/lib/utils/error-classifier.test.ts

@@ -0,0 +1,120 @@
+import { describe, it, expect } from 'vitest';
+import { classifyError, type ApiErrorType } from './error-classifier';
+
+describe('classifyError', () => {
+  // --- Rate limit ---
+  it('classifies "rate_limit_error" as rate_limit', () => {
+    const result = classifyError('rate_limit_error: Too many requests');
+    expect(result.type).toBe('rate_limit');
+    expect(result.retryable).toBe(true);
+    expect(result.retryDelaySec).toBeGreaterThan(0);
+  });
+
+  it('classifies "429" as rate_limit', () => {
+    const result = classifyError('HTTP 429 Too Many Requests');
+    expect(result.type).toBe('rate_limit');
+  });
+
+  it('classifies "too many requests" as rate_limit', () => {
+    const result = classifyError('Error: too many requests, please slow down');
+    expect(result.type).toBe('rate_limit');
+  });
+
+  it('classifies "throttled" as rate_limit', () => {
+    const result = classifyError('Request throttled by API');
+    expect(result.type).toBe('rate_limit');
+  });
+
+  // --- Auth ---
+  it('classifies "invalid_api_key" as auth', () => {
+    const result = classifyError('invalid_api_key: The provided API key is invalid');
+    expect(result.type).toBe('auth');
+    expect(result.retryable).toBe(false);
+  });
+
+  it('classifies "401" as auth', () => {
+    const result = classifyError('HTTP 401 Unauthorized');
+    expect(result.type).toBe('auth');
+  });
+
+  it('classifies "authentication failed" as auth', () => {
+    const result = classifyError('Authentication failed for this request');
+    expect(result.type).toBe('auth');
+  });
+
+  // --- Quota ---
+  it('classifies "insufficient_quota" as quota', () => {
+    const result = classifyError('insufficient_quota: You have exceeded your usage limit');
+    expect(result.type).toBe('quota');
+    expect(result.retryable).toBe(false);
+  });
+
+  it('classifies "billing" as quota', () => {
+    const result = classifyError('Error: billing issue with your account');
+    expect(result.type).toBe('quota');
+  });
+
+  it('classifies "credit" as quota', () => {
+    const result = classifyError('No remaining credit on your account');
+    expect(result.type).toBe('quota');
+  });
+
+  // --- Overloaded ---
+  it('classifies "overloaded" as overloaded', () => {
+    const result = classifyError('The API is temporarily overloaded');
+    expect(result.type).toBe('overloaded');
+    expect(result.retryable).toBe(true);
+  });
+
+  it('classifies "503" as overloaded', () => {
+    const result = classifyError('HTTP 503 Service Unavailable');
+    expect(result.type).toBe('overloaded');
+  });
+
+  // --- Network ---
+  it('classifies "ECONNREFUSED" as network', () => {
+    const result = classifyError('connect ECONNREFUSED 127.0.0.1:443');
+    expect(result.type).toBe('network');
+    expect(result.retryable).toBe(true);
+  });
+
+  it('classifies "ETIMEDOUT" as network', () => {
+    const result = classifyError('connect ETIMEDOUT');
+    expect(result.type).toBe('network');
+  });
+
+  it('classifies "fetch failed" as network', () => {
+    const result = classifyError('TypeError: fetch failed');
+    expect(result.type).toBe('network');
+  });
+
+  // --- Unknown ---
+  it('classifies unrecognized errors as unknown', () => {
+    const result = classifyError('Something weird happened');
+    expect(result.type).toBe('unknown');
+    expect(result.retryable).toBe(false);
+    expect(result.message).toBe('Something weird happened');
+  });
+
+  it('preserves original message for unknown errors', () => {
+    const msg = 'Internal server error: null pointer';
+    const result = classifyError(msg);
+    expect(result.message).toBe(msg);
+  });
+
+  // --- Message quality ---
+  it('provides actionable messages for rate_limit', () => {
+    const result = classifyError('rate_limit_error');
+    expect(result.message).toContain('Rate limited');
+  });
+
+  it('provides actionable messages for auth', () => {
+    const result = classifyError('invalid_api_key');
+    expect(result.message).toContain('Settings');
+  });
+
+  it('provides actionable messages for quota', () => {
+    const result = classifyError('insufficient_quota');
+    expect(result.message).toContain('billing');
+  });
+});

v2/src/lib/utils/error-classifier.ts

@@ -0,0 +1,121 @@
+// Error classifier — categorizes API errors for actionable user messaging
+
+export type ApiErrorType =
+  | 'rate_limit'
+  | 'auth'
+  | 'quota'
+  | 'overloaded'
+  | 'network'
+  | 'unknown';
+
+export interface ClassifiedError {
+  type: ApiErrorType;
+  message: string;
+  retryable: boolean;
+  /** Suggested retry delay in seconds (0 = no retry) */
+  retryDelaySec: number;
+}
+
+const RATE_LIMIT_PATTERNS = [
+  /rate.?limit/i,
+  /429/,
+  /too many requests/i,
+  /rate_limit_error/i,
+  /throttl/i,
+];
+
+const AUTH_PATTERNS = [
+  /401/,
+  /invalid.?api.?key/i,
+  /authentication/i,
+  /unauthorized/i,
+  /invalid.?x-api-key/i,
+  /api_key/i,
+];
+
+const QUOTA_PATTERNS = [
+  /insufficient.?quota/i,
+  /billing/i,
+  /payment/i,
+  /exceeded.*quota/i,
+  /credit/i,
+  /usage.?limit/i,
+];
+
+const OVERLOADED_PATTERNS = [
+  /overloaded/i,
+  /503/,
+  /service.?unavailable/i,
+  /capacity/i,
+  /busy/i,
+];
+
+const NETWORK_PATTERNS = [
+  /ECONNREFUSED/,
+  /ECONNRESET/,
+  /ETIMEDOUT/,
+  /network/i,
+  /fetch.?failed/i,
+  /dns/i,
+];
+
+function matchesAny(text: string, patterns: RegExp[]): boolean {
+  return patterns.some(p => p.test(text));
+}
+
+/**
+ * Classify an error message into an actionable category.
+ */
+export function classifyError(errorMessage: string): ClassifiedError {
+  if (matchesAny(errorMessage, RATE_LIMIT_PATTERNS)) {
+    return {
+      type: 'rate_limit',
+      message: 'Rate limited. The API will auto-retry shortly.',
+      retryable: true,
+      retryDelaySec: 30,
+    };
+  }
+
+  if (matchesAny(errorMessage, AUTH_PATTERNS)) {
+    return {
+      type: 'auth',
+      message: 'API key invalid or expired. Check Settings.',
+      retryable: false,
+      retryDelaySec: 0,
+    };
+  }
+
+  if (matchesAny(errorMessage, QUOTA_PATTERNS)) {
+    return {
+      type: 'quota',
+      message: 'API quota exceeded. Check your billing.',
+      retryable: false,
+      retryDelaySec: 0,
+    };
+  }
+
+  if (matchesAny(errorMessage, OVERLOADED_PATTERNS)) {
+    return {
+      type: 'overloaded',
+      message: 'API overloaded. Retrying shortly...',
+      retryable: true,
+      retryDelaySec: 15,
+    };
+  }
+
+  if (matchesAny(errorMessage, NETWORK_PATTERNS)) {
+    return {
+      type: 'network',
+      message: 'Network error. Check your connection.',
+      retryable: true,
+      retryDelaySec: 5,
+    };
+  }
+
+  return {
+    type: 'unknown',
+    message: errorMessage,
+    retryable: false,
+    retryDelaySec: 0,
+  };
+}