perf: overhaul session loading, caching, and runtime isolation (#2360)

Improve OpenChamber responsiveness under large session workloads while fixing
cache, synchronization, and persistence correctness across runtimes, projects,
directories, and worktrees.

- prioritize selected and visible sessions during bootstrap and defer
  non-critical enrichment work
- reduce redundant message loading, event processing, store publication, and
  hidden sidebar work
- prevent stale session and message requests from overwriting newer
  authoritative state
- preserve existing data when authoritative fetches fail instead of treating
  failures as successful empty responses
- scope session materialization, messages, drafts, queues, todos, pins,
  permissions, folders, tabs, Git state, and pull request data by runtime and
  directory identity
- harden runtime switching, reconnect, cleanup, mutation reconciliation, and
  persisted-state ordering
- preserve live subagent Task linkage when metadata arrives after an older
  message request or while streaming parts are suspended
- coalesce overlapping tail refreshes without losing newer refresh demand
- improve cold-session loading by moving deferrable work out of the critical
  bootstrap path
- isolate URL authentication, mobile credentials, native secrets, and other
  runtime-owned state across endpoint changes
- bound long-lived caches and remove avoidable allocations from event and
  rendering hot paths
- limit virtualization to archive collections where it improves rendering
  without disrupting active sidebar layout
- stabilize session folders, pin ordering, expanded state, and persisted
  sidebar behavior
- open skill files through the same secure editor and outside-workspace grant
  flow used by file navigation, including worktree sessions
- expand regression coverage for stale completions, runtime collisions,
  reconnect behavior, persistence races, authoritative empty results, and
  subagent refresh ordering
- document the updated synchronization, cache ownership, performance, and
  runtime-isolation invariants

packages/web/server/lib/opencode/env-runtime.js

@@ -347,9 +347,9 @@ export const createOpenCodeEnvRuntime = (deps) => {
       }
     }
 
-    // The bundled CLI is the LAST resort (see bundledOpenCodeCliFallback at the
-    // exit points below): a user's own OpenCode install — PATH, known install
-    // locations, or shell-resolved — must win over the pinned bundled copy.
+    const bundled = bundledOpenCodeCliFallback();
+    if (bundled) return bundled;
+
     const resolvedFromPath = searchPathFor('opencode');
     if (resolvedFromPath) {
       clearWslOpencodeResolution();
@@ -427,7 +427,7 @@ export const createOpenCodeEnvRuntime = (deps) => {
       // Do not auto-detect OpenCode from WSL. OpenCode sessions are keyed by
       // server-visible directories, and mixing Windows paths with WSL paths
       // creates duplicate/missing project state in the desktop app.
-      return bundledOpenCodeCliFallback();
+      return null;
     }
 
     const shells = [process.env.SHELL, '/bin/zsh', '/bin/bash', '/bin/sh'].filter(Boolean);
@@ -451,7 +451,7 @@ export const createOpenCodeEnvRuntime = (deps) => {
       }
     }
 
-    return bundledOpenCodeCliFallback();
+    return null;
   };
 
   const resolveNodeCliPath = () => {