[copybara-service]

feat(interactions): add automatic_continuation to interactions.create in the TypeScript SDK

Foreground interactions.create() calls are capped per request by the server (32k output tokens unary, 64k streaming) and stop with status='requires_continuation' plus a continuation_token. GeminiNextGenInteractions.create now accepts automatic_continuation (default true) on params and chains continuation hops client-side so a plain create() returns the full decode.

Request chaining:

• Each hop after the first sends the continuation_token from the previous hop. With store !== false (default) it sets previous_interaction_id to the hop that issued the token and omits input; with store: false it resends the original input.
• Unary foreground model calls default generation_config.max_output_tokens to 65536 when unset without mutating caller objects (streaming uses the server's 64k default). Explicit values are never overridden.
• Stops on completed, incomplete (token preserved for manual resumption), requires_action, failed, cancelled, a missing token, or a repeated token. Skipped for agent / agent_config requests and background: true; background: true with automatic_continuation: false throws an error upfront.

Unary (stream: false) merging:

• Hops are merged into one Interaction: steps concatenated in hop order (leading user_input steps dropped on later hops), usage counts and per-modality breakdowns summed across hops with usage.initial_input_tokens taken from hop 1, id / status / continuation_token / updated from the final hop, and previous_interaction_id / created / input from hop 1.
• continuation_ids lists every hop id in order, de-duplicated with any server-provided ids. output_text skips intervening thought steps across hop boundaries.

Streaming (stream: true):

• Events from all hops are yielded verbatim on a pull-on-demand Stream<InteractionSSEEvent>. Consumers should treat interaction.completed with status='requires_continuation' as intermediate.
• Mid-hop transport drops or premature EOF resume from the latest interaction.status_update checkpoint token when no content was yielded since that checkpoint (up to 3 no-progress reconnects). SSE error events are terminal; HTTP status retries stay with options.retries.

Timeouts and errors:

• Numeric per-call options.timeout_ms (and alias options.timeout) bounds the whole create() call across hops via CallDeadline. Client-level httpOptions.timeout, options.retries, and AbortSignal apply per hop.
• A failure or timeout after progress throws ContinuationInterruptedError (cause chained) carrying partialInteraction (unary), continuationToken, interactionId, and continuationIds so billed work is preserved for manual resumption. First-hop failures propagate unchanged.

Opt-out:

• automatic_continuation: false returns the single server response untouched (no budget injection, no merging) and emits a one-time console.warn if it stops at requires_continuation without a caller-supplied continuation_token.

Tests: test/unit/interactions_continuation_conformance_test.ts (52 conformance cases) and test/unit/interactions_continuation_test.ts (whole-call timeout, wire hygiene, stream cancellation, and exports).