feat: session goals - server-driven goal loop with independent small-model audit (#2148)

Arm the target button in the composer and the next prompt becomes a goal:
the server keeps the session working toward it (idle tick -> small-model
audit -> continuation) until the objective is verifiably complete, blocked,
or out of budget — even with the UI closed.

Server (packages/web/server/lib/session-goal):
- event-driven loop on the global SSE hub; goal state lives in
  session.metadata.openchamber.goal (merge-safe patches, stale-write guard
  by goal id), so it survives restarts and syncs to every client for free
- the small-model audit (objective + last assistant turn only, language
  pinned to the objective) is the sole termination authority; blocked needs
  3 consecutive verdicts, audit outages tolerate one unaudited continuation
  then stop the goal as resumable-blocked
- hard stops: optional token budget, auto-continuation cap (Resume grants a
  fresh allowance), turn errors; user abort pauses the goal instead of
  blocking it, and resuming over an aborted tail nudges immediately
- token accounting as a snapshot of the latest turn (input + cache.read +
  output), goal-relative via a creation baseline and segmented across
  compactions; a compaction summary skips the audit and continues
- continuations reuse the session's own provider/model/agent/variant

UI:
- three-mode target button (arm / disarm / manage dialog), informational
  goal strip with inline pause/resume and an Evaluating indicator, sidebar
  state glyph, objective length counter (2000-char server clamp),
  read-only completed goals
- goal entry points: composer (sessions and drafts), start-new-session-
  from-answer dialog, plan implement dialog (plan content becomes the
  objective), scheduled tasks (Run as goal + budget)
- Settings -> Chat -> Goal: feature toggle + default token budget with
  three-layer parity (web server, client persistence, VS Code bridge);
  VS Code renders goal state but hides the entry points (the loop runs in
  the web server only)

Notifications: per-turn "ready" notifications are suppressed while a goal
is active; settling sends one final notification (desktop, web-push, APNs
generic titles with the session name as body) honoring the completion
toggle. Error/question/permission notifications are untouched.

Docs: user guide (session-goals) in all 9 locales + sidebar entry,
scheduled-tasks cross-reference, server module DOCUMENTATION.md.

packages/ui/src/components/chat/ChatInput.tsx

@@ -100,6 +100,8 @@ import {
 } from './attachmentCitations';
 import { getFileMentionAutocompleteQuery, type FileMentionAutocompleteInputSource } from './fileMentionAutocompleteState';
 import { SessionSuggestionChip } from '@/components/chat/SessionSuggestionChip';
+import { SessionGoalRow } from '@/components/chat/SessionGoalRow';
+import { SessionGoalButton, SessionGoalObjectiveCounter } from '@/components/chat/SessionGoalButton';
 import type { Part } from '@opencode-ai/sdk/v2/client';
 
 const MAX_VISIBLE_TEXTAREA_LINES = 8;
@@ -4904,6 +4906,11 @@ const ChatInputComponent: React.FC<ChatInputProps> = ({ onOpenSettings, scrollTo
                 >
                 {isMobile && !mobileComposerExpanded ? (
                     <div className="flex flex-col">
+                    <SessionGoalRow
+                        sessionId={currentSessionId}
+                        directory={currentSessionDirectoryForSync ?? currentDirectory}
+                        className="mb-1.5"
+                    />
                     <SessionSuggestionChip
                         sessionId={currentSessionId}
                         directory={currentSessionDirectoryForSync ?? currentDirectory}
@@ -4986,6 +4993,11 @@ const ChatInputComponent: React.FC<ChatInputProps> = ({ onOpenSettings, scrollTo
                     </div>
                 ) : (
                 <>
+                <SessionGoalRow
+                    sessionId={currentSessionId}
+                    directory={currentSessionDirectoryForSync ?? currentDirectory}
+                    className="mb-1.5"
+                />
                 <SessionSuggestionChip
                     sessionId={currentSessionId}
                     directory={currentSessionDirectoryForSync ?? currentDirectory}
@@ -5313,6 +5325,14 @@ const ChatInputComponent: React.FC<ChatInputProps> = ({ onOpenSettings, scrollTo
                                             permissionAutoAcceptEnabled={permissionAutoAcceptEnabled}
                                             handlePermissionAutoAcceptToggle={handlePermissionAutoAcceptToggle}
                                         />
+                                        <SessionGoalButton
+                                            sessionId={currentSessionId}
+                                            directory={currentSessionDirectoryForSync ?? currentDirectory}
+                                            draftOpen={newSessionDraftOpen}
+                                            footerIconButtonClass={footerIconButtonClass}
+                                            iconSizeClass={iconSizeClass}
+                                        />
+                                        <SessionGoalObjectiveCounter length={message.length} />
                                     </div>
                                     <div className="flex items-center min-w-0 gap-x-1 justify-end">
                                         <div className="flex items-center gap-x-1 flex-shrink-0">
@@ -5382,6 +5402,15 @@ const ChatInputComponent: React.FC<ChatInputProps> = ({ onOpenSettings, scrollTo
                                         handlePermissionAutoAcceptToggle={handlePermissionAutoAcceptToggle}
                                         withTooltip
                                     />
+                                    <SessionGoalButton
+                                        sessionId={currentSessionId}
+                                        directory={currentSessionDirectoryForSync ?? currentDirectory}
+                                        draftOpen={newSessionDraftOpen}
+                                        footerIconButtonClass={footerIconButtonClass}
+                                        iconSizeClass={iconSizeClass}
+                                        withTooltip
+                                    />
+                                    <SessionGoalObjectiveCounter length={message.length} />
                                 </div>
                                 <div className={cn('flex items-center flex-1 justify-end', footerGapClass, 'md:gap-x-3')}>
                                     <MemoModelControls className={cn('flex-1 min-w-0 justify-end')} />