Documented which providers receive strict tool schemas

documentation/Tools.md

@@ -24,7 +24,9 @@ Adding a provider API means writing an `IToolCallingProviderAdapter`, not anothe
 
 `Function.Parameters` is plain JSON Schema: an optional argument is simply absent from `required`. That is what `ToolParameterSchemaBuilder` writes, and Anthropic reads it as written.
 
-OpenAI's strict mode wants it differently. It insists that **every** property appear in `required`, so an argument that may be left out has to say so by allowing null instead — `"type": ["string", "null"]`, plus `null` among its enum values where it has any. `OpenAIStrictToolSchema.FromToolParameters` therefore converts on the way out, for both OpenAI shapes and only where `Strict` is set. Nothing is lost, because a tool treats an absent argument and a null one the same way.
+OpenAI's strict mode wants it differently. It insists that **every** property appear in `required`, so an argument that may be left out has to say so by allowing null instead — `"type": ["string", "null"]`, plus `null` among its enum values where it has any. `OpenAIStrictToolSchema.FromToolParameters` therefore converts on the way out, but only where strict mode is kept. Nothing is lost there, because a tool treats an absent argument and a null one the same way.
+
+Strict mode is a promise of the host, not of the definition: only a host which binds the model's output to the schema keeps it. OpenAI does so in both of its APIs, and Anthropic does so without needing any conversion. Anywhere else, the converted schema would only tell the model that every argument is required. Groq, which validates a tool call against the schema without binding the model to it, then rejects each call that leaves an optional argument out, and other models fill the gap with placeholders such as `0` that the tool has to refuse. Every other Chat Completions host therefore gets the schema as written, with `strict: false`. A host which does bind tool calls says so by passing `enforcesStrictToolSchemas: true` to `StreamOpenAICompatibleChatCompletion`, as `ProviderOpenAI` does, next to the page that documents it. `ToolFunctionDefinition.Strict` works the other way round: set to false, it keeps a tool out of strict mode everywhere, for a schema strict mode cannot express.
 
 So the canonical schema is provider-neutral, and the provider that wants something else translates away from it in its own adapter. That is where the next such conversion belongs too — not in the definition.
 
@@ -58,7 +60,7 @@ When a tool returns data that future messages must only send to providers at or
 
 ## Security
 
-Treat model-provided tool arguments as untrusted input.
+Treat model-provided tool arguments as untrusted input. Refuse a wrong one rather than guessing what it meant: a placeholder such as `0` is not a page, and reading it as "no page" does something the model did not ask for. The model reads the refusal and tries again, so the message has to name the argument and the value that arrived, say what would be valid, and, for an optional argument, that leaving it out is always possible. `WebSearchTool` shows the pattern.
 
 For tools that perform network requests:
 
@@ -107,7 +109,7 @@ Every successfully retrieved page with readable content is also returned as a st
 - Put every argument and setting name in a constant that the schema and the reading code share.
 - Set `MinimumProviderConfidence` to what the tool actually exposes.
 - Mark a setting the tool cannot work without as `Required`, rather than saying so in its description.
-- Validate settings and model arguments.
+- Validate settings and model arguments, and refuse a wrong argument with a message the model can correct itself from.
 - Filter content fetched from outside AI Studio for prompt injections, and declare `ReturnsUntrustedExternalContent`.
 - Protect secrets and sensitive trace arguments.
 - Add provider-confidence checks when tool output may contain sensitive data.