Default Responses history to unlimited (-1)

[Copilot]

The default 100-item history limit can discard conversation context and separate tool calls from their results. Increasing the limit only postpones truncation.

• Defaults: Change server, context, and orchestration history limits to -1 (unlimited), including persisted history references.
• Configuration: Accept -1 through constructor options and environment parsing; retain positive limits and reject zero or other negative values.
• Providers: Return all history for -1 in file and in-memory stores; forward the value unchanged to Foundry.
• Contracts: Update documentation, API snapshots, and regression coverage for history exceeding 100 items across stored turns.

Explicit limits remain available:

app = ResponsesAgentServerHost(
    options=ResponsesServerOptions(default_fetch_history_count=1000),
)

Unlimited history removes item-count truncation, not model context-window limits or the need for summarization.

[azure-pipelines]

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