[BUG]

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?

SendMessage (cross-session messaging) became completely unavailable after a
system crash and an app update that landed around the same time. Not a
delivery failure — the tool cannot be loaded at all. ToolSearch for
"SendMessage" returns "No matching deferred tools found." ListAgents
continues to work normally throughout and correctly lists live peer
sessions, which rules out "no valid target" as the explanation.

What Should Happen?

SendMessage should be loadable via ToolSearch whenever ListAgents shows
valid peer sessions, or fail with a clear error - not silently vanish from
the deferred tool list while a related tool (ListAgents) keeps working.

Error Messages/Logs

ToolSearch result for "select:SendMessage":
"No matching deferred tools found."

ListAgents result (working correctly, for contrast):
"Peer sessions (7): [... 7 valid named sessions listed ...]"

Steps to Reproduce

1. Run several concurrent Claude Code sessions on one Windows machine,

coordinating via SendMessage/ListAgents.

1. Machine suffers a hard crash (in our case a Windows BSOD, bugcheck 0x1a

MEMORY_MANAGEMENT) that kills every session.

1. Claude desktop app auto-updates around the same time as recovery.
2. Reopen sessions after reboot.
3. Call ToolSearch for "SendMessage" - returns no results, despite

ListAgents correctly showing multiple live peer sessions.

1. Fully quit and restart the Claude desktop app - no change.
2. Run a "repair" install of the Claude desktop app - ListAgents' own

descriptive text changes (begins saying peer messaging is "available"),
but SendMessage still will not load via ToolSearch, re-tested against a
fresh set of 7 live peer sessions.

Claude Model

Not sure / Multiple models

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.183

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Other

Additional Information

claude --version reports 2.1.183, which is OLDER than v2.1.259 in the
public changelog (github.com/anthropics/claude-code) - a release from the
day before this incident that specifically touched a related bug: "a
session that moved to the background appearing twice in ListAgents." If
that's not the actual version that updated, it may be worth checking
whether the desktop app shell carries a separate version number from this
CLI engine.

Possibly related: #86014 (different symptom - reports success but doesn't
deliver), #44080, #42737 (older reports of the same "listed but not
loadable" pattern in earlier version ranges).