[BUG] .mcpb install is a silent no-op on Claude Desktop 1.12603.1 (macOS): "Handling DXT/MCPB file" logs with no preview/install dialog and no error; identical binary works via manual claude_desktop_config.json

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Summary

On Claude Desktop 1.12603.1 (macOS), opening a local .mcpb no longer reliably
installs. The main process logs Handling DXT/MCPB file: <path> (often once per
double-click), then nothing happens — no install/preview dialog appears, no
extension is installed, and no error is surfaced to the user or written to the log.
The exact same .mcpb/binary installs and runs fine when registered manually via
claude_desktop_config.json, so the package itself is valid — the failure is in the
.mcpb install/preview path.

This is intermittent: the identical file installed successfully earlier the same
day on the same app version, then later only produced the no-op.

## Environment (verified on the affected machine)

• Claude Desktop: 1.12603.1 (CFBundleShortVersionString and CFBundleVersion both 1.12603.1)
• macOS: 14.5 (23F79), Apple Silicon (arm64)
• Package: manifest_version: "0.3", server.type: "binary", unsigned (adhoc-signed binary), entry_point a

self-contained PyInstaller bundle

• Org allowlist: disabled; extension blocklist: 0 entries (so policy is not the cause — see evidence

D)

## Expected
Opening a .mcpb shows the install/preview dialog and installs the extension (or
surfaces a clear error if it can't).

## Actual
Handling DXT/MCPB file is logged, then no dialog, no install, and no error.

## Evidence (verbatim from ~/Library/Logs/Claude/main.log)

A) The no-op — opening the .mcpb logs only "Handling …", nothing follows:
2026-06-13 20:58:39 [info] Handling DXT/MCPB file: /Users/<user>/.../build/voiceswap-tools.mcpb
2026-06-13 20:58:40 [info] Handling DXT/MCPB file: /Users/<user>/.../build/voiceswap-tools.mcpb
2026-06-13 20:58:41 [info] Handling DXT/MCPB file: /Users/<user>/.../build/voiceswap-tools.mcpb
2026-06-13 20:58:43 [info] Handling DXT/MCPB file: /Users/<user>/.../build/voiceswap-tools.mcpb
2026-06-13 20:58:44 [info] Handling DXT/MCPB file: /Users/<user>/.../build/voiceswap-tools.mcpb
2026-06-13 20:58:49 [info] Handling DXT/MCPB file: /Users/<user>/.../build/voiceswap-tools.mcpb
No Installing unsigned extension, Successfully installed extension, or
Failed to preview DXT/MCPB extension line follows these entries.

B) The identical file DID install earlier the same day on the same version (so it's intermittent, not a
hard reject):
2026-06-13 14:21:33 [warn] Installing unsigned extension from /Users/<user>/.../build/voiceswap-tools.mcpb
2026-06-13 14:21:35 [info] Successfully installed extension local.mcpb.voiceswap-team.voiceswap-tools-mcp
v0.1.8
2026-06-13 17:14:03 [warn] Installing unsigned extension from /Users/<user>/.../build/voiceswap-tools.mcpb
2026-06-13 17:14:05 [info] Successfully installed extension local.mcpb.voiceswap-team.voiceswap-tools-mcp
v0.1.8

D) Policy is not the cause — allowlist disabled, blocklist empty:
2026-06-13 21:06:33 [info] Organization allowlist enabled: false
2026-06-13 21:06:34 [info] Successfully fetched blocklist from .../dxt/blocklist with 0 entries

What Should Happen?

Expected

Opening a .mcpb shows the install/preview dialog and installs the extension (or
surfaces a clear error if it can't).

## Actual
Handling DXT/MCPB file is logged, then no dialog, no install, and no error.

Error Messages/Logs

Steps to Reproduce

## Reproduction

1. On Claude Desktop 1.12603.1 (macOS), open/double-click a valid local .mcpb.
2. Observe Handling DXT/MCPB file in ~/Library/Logs/Claude/main.log with no

subsequent preview/install/error and no UI dialog.

1. (Same machine) register the identical bundled binary via

claude_desktop_config.json → it launches and serves tools normally.

## Workaround (confirmed)
Registering the same self-contained executable directly in
claude_desktop_config.json under mcpServers connects and serves tools fine. This
bypasses the .mcpb install path entirely.

## Additional context / possible contributing factor (same-machine observation, may not generalize)
The .mcpb install path appears to make a server-side can_install round-trip
(.../dxt/can_install). On this machine, several of the no-op occurrences coincided
with logged auth/connectivity errors in the same window, e.g.:
[error] Cannot get base query config: oauth failed (not_logged_in): cache cleared mid-flow
[error] ... The internet connection appears to be offline (ERR_INTERNET_DISCONNECTED)
Regardless of cause, the install path surfaces no error to the user when it fails —
the silent no-op is itself the core defect.

## Possibly-separate secondary observation
A successfully-installed local .mcpb extension is deleted on the next app startup,
even though its can_install verdict is canInstall: true, the allowlist is disabled,
and the blocklist is empty:
... verdict: { extensionId: 'local.mcpb.voiceswap-team.voiceswap-tools-mcp', canInstall: true, reason:
undefined }
2026-06-13 17:13:42 [info] Deleting extension local.mcpb.voiceswap-team.voiceswap-tools-mcp
2026-06-13 17:13:42 [info] Successfully deleted extension local.mcpb.voiceswap-team.voiceswap-tools-mcp
2026-06-13 18:08:50 [info] Deleting extension local.mcpb.voiceswap-team.voiceswap-tools-mcp
2026-06-13 18:08:50 [info] Successfully deleted extension local.mcpb.voiceswap-team.voiceswap-tools-mcp
This may be a distinct bug from the install no-op; flagging in case it's related.

## Corroboration (other reports, not observed by me — please verify)
Other users have reported similar .mcpb install failures appearing after the
1.12603.1 update (built ~2026-06-11), on both macOS (handleDxtFile path) and
Windows/MSIX (.mcpb Preview/Install closing silently while "Install Unpacked
Extension" still works). This issue is the macOS data point with full logs.

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

Claude 1.12603.1 (3df4fd) 2026-06-11T16:57:36.000Z

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Warp

Additional Information

_No response_