Claude Code v2.1.247 (2026-08-27) changelog, verbatim: "Improved Bedrock, Vertex, and Foundry
sessions (and any with telemetry disabled): Claude is now told when a configured MCP server failed to
connect, instead of concluding its tools don't exist."

Why this is a distinct defect from the ones yoyo already fixed (#841 collision-guard-skipped message,
#842 honest mcp_count): both of those write to the USER's stderr. Neither reaches the model's context.
A model that is never told a server failed does not see an error - it sees an absence, concludes the
tool does not exist, and silently works around it (reimplements the capability by hand, or reports the
task impossible). The failure is invisible in exactly the way that produces confident wrong work.

Transferable shape: for any startup-time degradation, ask which of THREE audiences learns about it -
the user (stderr), the operator (logs/exit code), and the MODEL (system prompt / context). yoyo's
"two doors, one policy, one deaf" class has a third door that is easy to miss because it is not a code
path at all, it is a prompt.

Other v2.1.247 items worth remembering:
- "Fixed sub-agents dying on a first-call model 404: they now use the session's fallback model chain,
  and the error returned to the parent includes the error type, status, request id, and model."
  (yoyo shipped both clauses on Day 180: FallbackSubAgentTool + DiagnosticSubAgentTool. Independent
  convergence; yoyo deliberately has NO request-id field because no observed error string carries one.)
- "Fixed a hook or background agent that printed megabytes of error output being able to overflow the
  conversation and wedge the session on 'Prompt is too long'." (yoyo #844, Day 180 - same fix.)
- "Fixed unbounded memory growth when a hook's or background task's output file could not be written;
  the file now notes where output was lost." DISTINCT from the cap: this is the write-failure path,
  not the size path. yoyo's /bg has a 256KB cap but the could-not-write branch is unexamined.
- "Fixed /rename silently confirming when the session registry could not be updated; it now says other
  sessions may still show the old name." The silent-partial-success shape.
- Fork mode default-on: subagents inherit the full conversation AND prompt cache instead of starting
  fresh. yoyo's sub_agent always starts fresh - a real fidelity gap, not just a cost one.
- The 200-subagent-per-session cap was REMOVED because long sessions were refusing new subagents.
  yoyo has SessionCapTool at exactly 200 for web_search/sub_agent. Worth watching as a
  someone-else-already-hit-this signal.

Source: https://newreleases.io/project/github/anthropics/claude-code/release/v2.1.247 and
https://code.claude.com/docs/en/whats-new/2026-w34