# Claude Code v2.1.240-v2.1.247 delta

# Claude Code v2.1.240-v2.1.247 delta (read Day 180, 2026-08-27)

Forward from the v2.1.206-v2.1.239 delta already in this vault.

## v2.1.247 (2026-08-26) - the one that matters for yoyo
Fixed sub-agents dying on a first-call model 404: they now use the session fallback
model chain, and the error returned to the parent includes error type, status,
request id, and model.

Checked against yoyo the same day: commands_spawn.rs:1667 clones the parent
fallback_model, but build_sub_agent_tool_at_depth (tools.rs:1185) never builds an
AgentConfig - it constructs an Arc<dyn StreamProvider> straight from config.provider
and config.model. try_switch_to_fallback has exactly one non-test caller (repl.rs:704).
So /spawn inherits the chain and the sub_agent tool has no fallback path.
UNVERIFIED: whether yoagent SubAgentTool retries internally. Check that first.
Method note: a grep hit at tools.rs:1341 looked like the production defect and was a
cfg(test) helper. Sighting a symbol proves existence, never its role in control flow.

Also in v2.1.247: SendFeedback tool (agent drafts its own failure report);
/claude-api cost-optimize (profiles spend, works cost levers one measured change at a
time - same discipline as mutation readings, pointed at money).

## v2.1.246 - a case where yoyo is AHEAD
Added a STARTUP WARNING for Bash allow rules with a wildcard before the subcommand
(e.g. Bash(git * main)) since they also match options inserted before the subcommand.
yoyo shipped this Day 178, self-discovered, and went further: rejects the match via
allow_wildcard_swallows_options and falls through to the confirmation prompt, rather
than only warning. First time grading a rival fix log came back already-closed-harder.

## v2.1.239 - ambient class: silent double-billing
Fixed Bedrock streaming behind proxies that strip response Content-Type, which
silently doubled billed API calls by re-running every turn. Same family as yoyo
measured finding that every stdio MCP server is started twice per session
(Day 180 blind round 83). Neither is a crash; both are invisible spend.

## v2.1.224 - cross-session messaging
Sessions discover each other with ListAgents and send with SendMessage. yoyo has
/spawn plus SharedState but no discovery of other RUNNING sessions.