feat(laguna): add poolside/Laguna-S-2.1 support via a dedicated renderer

[eexwhyzee]

Summary

Adds renderer support for poolside/Laguna-S-2.1, a larger sibling of XS-2.1.

S-2.1 shares XS-2.1's tokenizer (same vocab, merges, and special tokens/ids) but ships a different chat template: it defaults enable_thinking to True (XS-2.1 defaults False) and adds a preserve_thinking kwarg that widens the reasoning-display gate to enable_thinking or preserve_thinking. The token format is otherwise identical.

Note: an earlier version of this PR routed S-2.1 to the existing XS-2.1 renderer on the assumption the chat template was byte-identical. It isn't — that mismatched apply_chat_template on the default thinking flag (bare </think> vs an empty <think></think> wrapper) and failed test_render_ids / test_build_helpers. (The config-parity barrage missed it because it always sets enable_thinking explicitly, never exercising the differing default.) This PR now gives S-2.1 its own renderer/config.

Changes

• LagunaS21RendererConfig — enable_thinking=True, preserve_thinking=False defaults, matching S-2.1's template. Registered in the discriminated union, _CONFIG_BY_NAME, and exports.
• LagunaS21Renderer — a thin LagunaXS21Renderer subclass that overrides only the reasoning-display gate (enable_thinking or preserve_thinking); everything else (role tags, tool-call packing, system-block gate, generation prompt, parse skeleton) is inherited unchanged.
• Route poolside/Laguna-S-2.1 → laguna-s-2.1 in MODEL_RENDERER_MAP; register the renderer; lazy-import + exports.
• Typing follows the existing GLM5/Nemotron subclass idiom (base __init__ accepts the config union; subclass narrows self.config).

Testing

• Full suite: 2700 passed, 128 skipped, 1 xfailed, 0 failures.
• New tests/test_laguna_s21.py: token-exact parity vs apply_chat_template for all four enable_thinking × preserve_thinking combinations, plus the thinking-on default and the preserve_thinking history-retention behaviour.
• S-2.1 added to the shared render-parity matrices (config-parity, is_content, sampled_mask, render_ids, build_helpers) — all green.
• ruff + ty clean (no new diagnostics vs main).

🤖 Generated with Claude Code

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Note

Low Risk
Additive model routing and a small renderer subclass with focused parity tests; no changes to auth, data handling, or existing Laguna render paths beyond a shared hook in XS-2.1 assistant rendering.

Overview
Adds first-class support for poolside/Laguna-S-2.1, which shares XS-2.1’s tokenizer but uses a different chat template ( enable_thinking defaults to True and a new preserve_thinking kwarg gates whether historical <think> blocks render).

LagunaS21RendererConfig and LagunaS21Renderer (a thin LagunaXS21Renderer subclass) implement that template: the subclass only overrides the reasoning-display gate to enable_thinking or preserve_thinking. LagunaXS21Renderer now routes assistant history through _render_history_reasoning() so XS-2.1 and S-2.1 can diverge without duplicating render logic.

Wiring updates map the checkpoint in MODEL_RENDERER_MAP, register laguna-s-2.1 in the config union/registry/exports, and document the variant in README and docs/renderer-config.md. tests/test_laguna_s21.py plus shared parity matrices cover auto-resolution, default thinking-on behavior, all flag combinations vs apply_chat_template, and preserve_thinking when thinking is off.

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Note

Add LagunaS21Renderer for the poolside/Laguna-S-2.1 model

• Introduces LagunaS21Renderer in renderers/laguna_xs2.py as a subclass of LagunaXS21Renderer, with a dedicated LagunaS21RendererConfig (in renderers/configs.py) that adds a preserve_thinking flag alongside the existing enable_thinking.
• Reasoning blocks in message history are retained when either enable_thinking or preserve_thinking is True; both default to True and False respectively, so thinking is on by default.
• Auto-resolution maps poolside/Laguna-S-2.1 to laguna-s-2.1 in MODEL_RENDERER_MAP and the renderer registry.
• Adds a full test suite in tests/test_laguna_s21.py covering auto-resolution, default behavior, flag combinations, and history reasoning drop/preserve logic.

^{Macroscope summarized 29606c6.}

[macroscopeapp]

Approvability

Verdict: Needs human review

This PR adds a new renderer and config for the Laguna-S-2.1 model. While the implementation is clean and well-tested, it introduces new user-facing capability and new components, which warrants human review per repository standards.

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