Claude Opus 4.7 + ultracode: 50min/37% budget burned, total failure on Chrome Native Messaging integration on Win11

Summary

I asked Claude Opus 4.7 with the ultracode multi-agent workflow to wire up a Chrome right-click context menu that spawns a Claude Code session with a /paper slash command pre-filled. The slash command and skill pieces were trivial and worked. The Chrome integration burned roughly 50 minutes and ~37% of my token budget and ended in total failure, with the workflow itself crashing partway through.

I want to flag both the technical dead-ends Claude walked into and the planning/harness failures that made it expensive.

What Claude tried (in order)

1. Windows custom URL protocol (claudecode://). HKCU registration was silently ignored by Windows 11 26200. HKLM registration auto-elevated via UAC, and the elevated launcher then couldn't see the user's PATH / non-elevated file locations. Dead end.
2. Chrome Native Messaging with a .bat/.cmd host wrapper. Chrome rejected it: Specified native messaging host not found.
3. Real C# .exe host compiled with csc.exe. I wrote a self-test that piped Chrome's exact stdin length-prefixed protocol through the binary end-to-end — it passed. The host is demonstrably correct.
4. Full integration attempt with the working .exe + a byte-perfect manifest modeled on com.anthropic.claude_browser_extension (which works on the same machine) + correct HKCU NativeMessagingHosts registration + matching extension ID in allowed_origins + nativeMessaging permission in manifest.json + full Chrome restart (51 processes killed) + HKLM fallback registration. Chrome still returned Specified native messaging host not found. Never resolved.

Machine: Windows 11 Pro 10.0.26200, Chrome 64-bit at C:\Program Files\Google\Chrome\Application\chrome.exe, extension loaded as unpacked in Profile 1 (not Default). Other native messaging hosts on the same machine (Anthropic's own, ShareX, Microsoft, Apple) work fine, so this is not a global Chrome/registry problem.

Workflow failure

Mid-run, the ultracode workflow died with subagent completed without calling StructuredOutput (after 2 in-conversation nudges). About 46 minutes and ~250k tokens of subagent work were thrown away with no surfaced output. The structured-output retry mechanism is not robust enough — agents are dropping the final tool call even with two nudges.

Model/harness failures Claude should own

• No backtracking to a simpler architecture. After URL protocols failed, the obvious move was a tiny localhost HTTP server the extension POSTs to. Instead Claude doubled down on Native Messaging across four sub-attempts. Sunk-cost iteration over re-planning.
• Pushed testing onto me. Almost every probe was "run this and tell me what happens" instead of Bash-driven verification. Five-second checks turned into multi-minute round-trips.
• No diagnostic visibility into Chrome's side. When Chrome says host not found but the registry key, manifest path, file ACLs, extension ID, and allowed_origins all check out, Claude has no way to ask Chrome why. There is presumably a chrome://-internal log or a --enable-logging --v=1 path it could have pointed me at much earlier.

Concrete suggestions

1. Ship a Native Messaging diagnostic recipe in the Claude Code docs/skills — the exact chrome.exe --enable-logging --v=1 invocation, where the log lands, and the strings to grep for. The current debugging loop is blind.
2. Make the StructuredOutput nudge mechanism resilient: if a subagent fails to emit structured output after N nudges, fall back to parsing the last assistant message rather than discarding the entire run. Losing 250k tokens to a missing tool call is brutal.
3. Bake an "architecture-reset" reflex into long-running coding workflows: after 2 failed attempts at the same integration mechanism, force a step back and enumerate alternatives before continuing to patch.
4. Prefer in-harness verification (Bash/PowerShell) over asking the user to run things, especially in ultracode where round-trips compound across agents.

Happy to share full transcript or a minimal repro of the host not found case if useful.