[Bug] Claude 4.6 Opus high effort degraded reasoning and web search behavior in problem-solving tasks

Bug Description
Opus currently often behaves more like Haiku. With Opus 4.6 high effort, I'm not used to it asking me for official Anthropic documentation without having looked it up on the internet itself first. It was explicitly tasked with solving the problem. But it didn't even research it. The solution was quick to find on GitHub. A few weeks ago, this was different. Back then, Opus still researched the web when the task was to solve a specific problem. In general, Opus 4.6 has gotten significantly worse. More errors, less proactive.
Environment Info

• Platform: win32
• Terminal: windows-terminal
• Version: 2.1.107
• Feedback ID: 687bde14-045a-420a-b273-db7cf9802ec5

Errors

[{"error":"Error: EEXIST: file already exists, mkdir 'C:\\Users\\Anwender\\.claude\\shell-snapshots'\n    at async <anonymous> (B:/~BUN/root/src/entrypoints/cli.js:1942:586)","timestamp":"2026-04-14T17:03:21.802Z"},{"error":"Error: ripgrep exited with code null\n    at <anonymous> (B:/~BUN/root/src/entrypoints/cli.js:549:2761)\n    at emit (node:events:98:22)\n    at #maybeClose (node:child_process:778:16)\n    at #handleOnExit (node:child_process:532:72)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-04-14T17:04:00.971Z"},{"error":"Error: Failed to fetch version from https://storage.googleapis.com/claude-code-dist-86c565f3-f756-42ad-8dfa-d59b1c096819/claude-code-releases/latest: Request failed with status code 429\n    at Vp4 (B:/~BUN/root/src/entrypoints/cli.js:2388:15184)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-04-14T19:16:41.809Z"},{"error":"Error: Failed to fetch version from https://storage.googleapis.com/claude-code-dist-86c565f3-f756-42ad-8dfa-d59b1c096819/claude-code-releases/latest: Request failed with status code 429\n    at Vp4 (B:/~BUN/root/src/entrypoints/cli.js:2388:15184)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-04-14T19:16:41.809Z"}]

Original answer from Opus when requested to solche the problem with secrets within Cowork:
Cowork Secrets Management: Is there an official way in the Cowork sandbox to provide secrets on a per-session basis (analogous to GitHub Actions Secrets)? If so → Option B becomes feasible.
Cowork Filesystem Mounts: Is ~/mnt/ mounted by default or only optionally? What exactly is the type (virtiofs/9p)? This determines whether file fallback #2 can ever work reliably.
Cowork Env Injection: Why doesn't settings.json.env end up in the VM? Is this a security feature or a bug?

Please provide links/paths to the Anthropic Cowork documentation, or I'll have to go with Option A (bootstrap script) — which works independently of Cowork-internal features.