feat(dashboard): add input history navigation with up/down arrows

Add shell-style up/down arrow navigation through past messages in the
SimpleInput component. History is derived from the conversation data
already parsed from session logs — no new state management needed.

dashboard/components/SessionCard.js:
- Pass `conversation` prop through to SimpleInput (line 170)
- Prop chain verified: App -> SessionCard -> SimpleInput, including
  the Modal/enlarged path (Modal.js:69 already passes conversation)

dashboard/components/SimpleInput.js:
- Accept `conversation` prop and derive `userHistory` via useMemo,
  filtering for role === 'user' messages and mapping to content
- Add historyIndexRef (-1 = not browsing) and draftRef (preserves
  in-progress text when entering history mode)
- ArrowUp: intercepts only when cursor at position 0 and autocomplete
  closed, walks backward through history (newest to oldest)
- ArrowDown: only when already browsing history, walks forward;
  past newest entry restores saved draft and exits history mode
- Bounds clamp on ArrowUp prevents undefined array access if
  userHistory shrinks between navigations (SSE update edge case)
- Reset historyIndexRef on submit (line 110) and manual input (line 141)
- Textarea height recalculated after setting history text via
  setTimeout to run after Preact commits the state update

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

dashboard/components/SessionCard.js

@@ -167,6 +167,7 @@ export function SessionCard({ session, onClick, conversation, onFetchConversatio
             status=${session.status}
             onRespond=${onRespond}
             autocompleteConfig=${autocompleteConfig}
+            conversation=${conversation}
           />
         `}
         </div>

dashboard/components/SimpleInput.js

@@ -2,7 +2,7 @@ import { html, useState, useRef, useCallback, useMemo, useEffect } from '../lib/
 import { getStatusMeta } from '../utils/status.js';
 import { getTriggerInfo as _getTriggerInfo, filteredSkills as _filteredSkills } from '../utils/autocomplete.js';
 
-export function SimpleInput({ sessionId, status, onRespond, autocompleteConfig = null }) {
+export function SimpleInput({ sessionId, status, onRespond, autocompleteConfig = null, conversation }) {
   const [text, setText] = useState('');
   const [focused, setFocused] = useState(false);
   const [sending, setSending] = useState(false);
@@ -12,8 +12,15 @@ export function SimpleInput({ sessionId, status, onRespond, autocompleteConfig =
   const [selectedIndex, setSelectedIndex] = useState(0);
   const textareaRef = useRef(null);
   const autocompleteRef = useRef(null);
+  const historyIndexRef = useRef(-1);
+  const draftRef = useRef('');
   const meta = getStatusMeta(status);
 
+  const userHistory = useMemo(
+    () => (conversation || []).filter(m => m.role === 'user').map(m => m.content),
+    [conversation]
+  );
+
   const getTriggerInfo = useCallback((value, cursorPos) => {
     return _getTriggerInfo(value, cursorPos, autocompleteConfig);
   }, [autocompleteConfig]);
@@ -100,6 +107,7 @@ export function SimpleInput({ sessionId, status, onRespond, autocompleteConfig =
       try {
         await onRespond(sessionId, text.trim(), true, 0);
         setText('');
+        historyIndexRef.current = -1;
       } catch (err) {
         setError('Failed to send message');
         console.error('SimpleInput send error:', err);
@@ -130,6 +138,7 @@ export function SimpleInput({ sessionId, status, onRespond, autocompleteConfig =
           const value = e.target.value;
           const cursorPos = e.target.selectionStart;
           setText(value);
+          historyIndexRef.current = -1;
           setTriggerInfo(getTriggerInfo(value, cursorPos));
           e.target.style.height = 'auto';
           e.target.style.height = e.target.scrollHeight + 'px';
@@ -169,6 +178,57 @@ export function SimpleInput({ sessionId, status, onRespond, autocompleteConfig =
             }
           }
 
+          // History navigation (only when autocomplete is closed)
+          if (e.key === 'ArrowUp' && !showAutocomplete &&
+              e.target.selectionStart === 0 && e.target.selectionEnd === 0 &&
+              userHistory.length > 0) {
+            e.preventDefault();
+            if (historyIndexRef.current === -1) {
+              draftRef.current = text;
+              historyIndexRef.current = userHistory.length - 1;
+            } else if (historyIndexRef.current > 0) {
+              historyIndexRef.current -= 1;
+            }
+            // Clamp if history shrank since last navigation
+            if (historyIndexRef.current >= userHistory.length) {
+              historyIndexRef.current = userHistory.length - 1;
+            }
+            const historyText = userHistory[historyIndexRef.current];
+            setText(historyText);
+            setTimeout(() => {
+              if (textareaRef.current) {
+                textareaRef.current.selectionStart = historyText.length;
+                textareaRef.current.selectionEnd = historyText.length;
+                textareaRef.current.style.height = 'auto';
+                textareaRef.current.style.height = textareaRef.current.scrollHeight + 'px';
+              }
+            }, 0);
+            return;
+          }
+
+          if (e.key === 'ArrowDown' && !showAutocomplete &&
+              historyIndexRef.current !== -1) {
+            e.preventDefault();
+            historyIndexRef.current += 1;
+            let newText;
+            if (historyIndexRef.current >= userHistory.length) {
+              historyIndexRef.current = -1;
+              newText = draftRef.current;
+            } else {
+              newText = userHistory[historyIndexRef.current];
+            }
+            setText(newText);
+            setTimeout(() => {
+              if (textareaRef.current) {
+                textareaRef.current.selectionStart = newText.length;
+                textareaRef.current.selectionEnd = newText.length;
+                textareaRef.current.style.height = 'auto';
+                textareaRef.current.style.height = textareaRef.current.scrollHeight + 'px';
+              }
+            }, 0);
+            return;
+          }
+
           // Normal Enter-to-submit (only when dropdown is closed)
           if (e.key === 'Enter' && !e.shiftKey) {
             e.preventDefault();