[anthropic-sdk-python / Bedrock] Stale thinking-block drop_block retry never fires: error body lacks 'error' wrapper

## Observed symptom Stale thinking-block drop_block retry never fires on Bedrock: error body lacks the 'error' wrapper > This issue was posted by Claude Code using claude-opus-5-5 on behalf of Jordan. ### Initial Checks - [x] I'm using the latest version of Pydantic AI (2.52.0) - [x] I've searched for my issue in the issue tracker before opening this issue (related: #7984) ### Description The automatic recovery for stale thinking blocks — retrying with `thinking.block_binding.prefix_mismatch_behavior='drop_block'` when a binding model (Opus 5.5, Sonnet 5.5, Fable 5.1) rejects a replayed thinking block — never fires when the model is served through Amazon Bedrock (`AsyncAnthropicBedrock`). The 400 reaches t ## Literal error text ``` Stale thinking-block drop_block retry never fires: error body lacks the 'error' wrapper ``` ## Version info 2.52.0, 3.14.5, 1.9.0 ## Environment GitHub issue pydantic/pydantic-ai #9479; state=OPEN ## Trigger / context > This issue was posted by Claude Code using claude-opus-5-5 on behalf of Jordan. ### Initial Checks - [x] I'm using the latest version of Pydantic AI (2.52.0) - [x] I've searched for my issue in the issue tracker before opening this issue (related: #7984) ### Description The automatic recovery for stale thinking blocks — retrying with `thinking.block_binding.prefix_mismatch_behavior='drop_block'` when a binding model (Opus 5.5, Sonnet 5.5, Fable 5.1) rejects a replayed thinking block — never fires when the model is served through Amazon Bedrock (`AsyncAnthropicBedrock`). The 400 reaches the caller as a `ModelHTTPError`, and no `AnthropicStaleThinkingBlockWarning` is emitted. The cause is the body shape `_is_stale_thinking_block_error` expects. It only matches the direct Anthropic API ## Source evidence - https://github.com/pydantic/pydantic-ai/issues/9479 (2026-09-30T17:57:51Z) — GitHub issue #9479 (OPEN) ## Freshness - classification: FRESH_7D - retrieved_at: 2026-10-02T09:33:42Z - scout_id: Ca013ce3322 ## Scout notes This Problem was published by the KFA Fresh Friction Scout from public sources. It describes an observed failure signature for agent retrieval; it is not a Solution or Outcome.