docs: update Mantle setup to reflect automatic shim detection

docs/bedrock.md

@@ -211,36 +211,38 @@ Mantle exposes the Anthropic Messages API for supported Claude models. Fast-agen
 ```yaml
 default_model: anthropic.claude-opus-4-7
 
-# ── Model Capabilities ──────────────────────────────────────────────────────
-# mantle: true is REQUIRED — it installs a Pallas-level provider override that
-# strips the features the Mantle endpoint rejects (anthropic-beta headers,
-# extended thinking, task budget, web tools, prompt caching). Without this
-# flag fast-agent sends those features and Mantle returns a misleading
-# 404 "model does not exist" error.
-model_capabilities:
-  vision: true
-  context_window: 1000000
-  max_output_tokens: 128000
-  mantle: true
-
 # ── Anthropic provider pointing at Mantle ────────────────────────────────────
 anthropic:
   base_url: "https://bedrock-mantle.us-east-1.api.aws/anthropic"
 ```
 
+That's the whole configuration. Pallas auto-detects the
+`bedrock-mantle` hostname in `anthropic.base_url` at startup and installs
+two compatibility shims so fast-agent's default request shape matches
+what Mantle expects (see `pallas/mantle_shims.py`):
+
+1. **Wire-name prefix** — re-adds the `anthropic.` prefix that fast-agent's
+   parser strips off, because Mantle requires the full
+   `anthropic.claude-opus-4-7` wire id. Without this shim you get
+   `404 "The model '...' does not exist"`.
+
+2. **`caller: null` strip** — drops the stray `caller` field Anthropic
+   SDK 0.100.x leaks onto replayed `tool_use` blocks (upstream issue
+   [anthropics/anthropic-sdk-python#1454](https://github.com/anthropics/anthropic-sdk-python/issues/1454)).
+   Mantle's validator rejects `caller: null` with `"tool_use.caller:
+   Input should be a valid dictionary or object"`, which would otherwise
+   break the MCP tool-use loop on the second turn.
+
 The Anthropic SDK appends `/v1/messages` to `base_url` automatically.
 
-> **Why `mantle: true` is required.** Fast-agent's built-in `ModelDatabase`
-> entries for Claude Opus 4.7 and Haiku 4.5 declare features that the
-> Anthropic API supports but the Mantle endpoint rejects —
-> `anthropic-beta: code-execution-web-tools-...` headers, extended thinking,
-> task budget, web search/fetch tools, and prompt caching in some
-> configurations. When Mantle sees a request carrying those features it
-> responds with a confusingly generic `{"type": "not_found_error",
-> "message": "The model '...' does not exist"}`. Pallas reads the `mantle`
-> flag and writes an entry into fast-agent's `_PROVIDER_MODEL_OVERRIDES`
-> dict for `(Provider.ANTHROPIC, <model>)` that strips those fields, so
-> fast-agent sends a plain Messages API request that Mantle accepts.
+**Feature support.** Mantle accepts the same Messages API request shape
+as `api.anthropic.com` once the shims are in place, including full MCP
+tool use (`tools`, `tool_use`/`tool_result` content blocks). Extended
+thinking, task budget, web_fetch/web_search server tools, and explicit
+prompt caching (`cache_control`) are not available via Mantle and should
+be left off in agent code when targeting Mantle — fast-agent's
+`ModelDatabase` entries already disable the ones the Anthropic SDK 0.100.x
+would otherwise auto-attach.
 
 
 ### `fastagent.secrets.yaml`