Add Claude 1M context window switching

[dibstern]

Summary

• Capture Claude subscription type and expose Sonnet context window options through model discovery.
• Add session-level context window switching from WebSocket handler through session overrides and prompt dispatch.
• Apply Claude SDK [1m] model IDs for Sonnet when selected, plus frontend selector, debug display, E2E, unit, and visual coverage.

Test Plan

• pnpm check
• pnpm lint
• pnpm test:unit
• pnpm build:frontend && pnpm exec playwright test --config test/e2e/playwright-variant.config.ts
• pnpm storybook:build
• pnpm exec playwright test --config test/visual/playwright.config.ts --grep "Model/ContextWindowSelector"
• pnpm test:all

Note

• .github/pull_request_template.md is not present in this checkout or on main; this body follows the repo's summary/test-plan shape from the implemented diff.

[Copilot]

Pull request overview

Adds end-to-end support for switching Claude Sonnet’s context window (200K vs 1M) by plumbing a new switch_context_window WebSocket message through session overrides, prompt dispatch, and the Claude SDK adapter model ID selection.

Changes:

• Extend discovery/capabilities to expose contextWindowOptions for Claude Sonnet models and capture Claude account subscriptionType to pick defaults.
• Add session-level context-window overrides and route switch_context_window messages through a new handler.
• Introduce a frontend ContextWindowSelector badge/dropdown plus E2E/unit/storybook coverage; update Claude adapter to apply [1m] model IDs and switch mid-session via query.setModel.

Reviewed changes

Copilot reviewed 40 out of 48 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
test/unit/stores/discovery-store.test.ts	Adds unit tests for context-window discovery store state/handlers.
test/unit/session/session-overrides.test.ts	Tests new context-window fields and per-session override behavior.
test/unit/session/session-overrides-effect.test.ts	Tests Effect-based overrides state for context windows.
test/unit/server/ws-router.stateful.test.ts	Updates routed message type list to include switch_context_window.
test/unit/server/ws-router.pbt.test.ts	Updates PBT message-type generator and drift-guard counts.
test/unit/server/ws-message-schemas.test.ts	Extends schema coverage tests for switch_context_window.
test/unit/provider/claude/claude-capabilities-probe.test.ts	Adds tests for subscriptionType + contextWindowOptions defaults.
test/unit/provider/claude/claude-adapter-send-turn.test.ts	Verifies [1m] suffix behavior and mid-session model switching.
test/unit/handlers/effect-handlers.test.ts	Adds handler tests for model_list contextWindowOptions + switching behavior.
test/unit/handlers/dispatch-effect.test.ts	Updates handler override mocks for context-window fields.
test/unit/bridges/client-init.test.ts	Verifies model_list includes contextWindowOptions on connect.
test/helpers/mock-factories.ts	Extends override mocks with context-window fields/methods.
test/e2e/specs/context-window-selector.spec.ts	New E2E coverage for context-window badge/dropdown and WS messages.
test/e2e/playwright-variant.config.ts	Runs the new context-window E2E spec in the variant config.
test/e2e/fixtures/mockup-state.ts	Adds mock init fixtures for context-window selector scenarios.
src/lib/shared-types.ts	Adds shared ContextWindowOption, schemas, and relay message type.
src/lib/session/session-overrides.ts	Adds context-window fields + getters/setters to session overrides.
src/lib/server/ws-router.ts	Adds switch_context_window to incoming message routing types.
src/lib/relay/poller-pre-filter.ts	Treats context_window_info as metadata (non-content) events.
src/lib/provider/types.ts	Adds provider-level context-window options and send-turn input field.
src/lib/provider/claude/types.ts	Tracks currentApiModelId for mid-session model changes.
src/lib/provider/claude/claude-capabilities-probe.ts	Computes contextWindowOptions and defaults based on subscription.
src/lib/provider/claude/claude-adapter.ts	Applies [1m] model IDs for Sonnet + switches via setModel.
src/lib/handlers/prompt.ts	Passes contextWindow override through to engine send_turn.
src/lib/handlers/payloads.ts	Adds switch_context_window payload typing.
src/lib/handlers/payload-schemas.ts	Adds schema validation for switch_context_window payloads.
src/lib/handlers/model.ts	Includes contextWindowOptions in Claude model_list entries.
src/lib/handlers/index.ts	Registers the new switch_context_window handler.
src/lib/handlers/context-window.ts	New handler to validate/apply context-window overrides + echo state.
src/lib/frontend/types.ts	Re-exports ContextWindowOption to frontend type surface.
src/lib/frontend/stores/ws-dispatch.ts	Routes context_window_info messages into the discovery store.
src/lib/frontend/stores/discovery.svelte.ts	Adds context-window discovery state + handler/getter.
src/lib/frontend/components/model/ModelSelector.svelte	Renders ContextWindowSelector alongside variant badge with mutual exclusion.
src/lib/frontend/components/model/ModelSelector.stories.ts	Resets new discovery state fields in story setup.
src/lib/frontend/components/model/ContextWindowSelector.svelte	New UI badge/dropdown for context window selection.
src/lib/frontend/components/model/ContextWindowSelector.stories.ts	New storybook coverage for defaults/selection/open state.
src/lib/frontend/components/debug/DebugPanel.svelte	Shows context_window_info messages in debug panel.
src/lib/effect/ws-message-schemas.ts	Adds Incoming WS schema for switch_context_window.
src/lib/effect/session-overrides-state.ts	Adds Effect-based default/per-session context-window state.
src/lib/bridges/client-init.ts	Adds contextWindowOptions into Claude entries in initial model_list.

Comments suppressed due to low confidence (2)

src/lib/bridges/client-init.ts:402

• The frontend’s ContextWindowSelector only renders when discoveryState.availableContextWindowOptions is populated via a context_window_info message, but client init currently never sends context_window_info (only variant_info). As a result the context-window badge/dropdown won’t appear on initial connect, even though model_list now includes contextWindowOptions. Consider emitting an initial context_window_info here (similar to the existing variant_info block) using the active model + current override/default, so the UI has options immediately.

						models: claudeCaps.models.map((m) => ({
							id: m.id,
							name: m.name,
							provider: "claude",
							...(m.limit ? { limit: m.limit } : {}),
							...(m.variants && Object.keys(m.variants).length > 0
								? { variants: Object.keys(m.variants) }
								: {}),
							...(m.contextWindowOptions && m.contextWindowOptions.length > 0
								? { contextWindowOptions: m.contextWindowOptions }
								: {}),
						})),
					});
					wsHandler.sendTo(clientId, { type: "model_list", providers });
				}
			} catch {
				// Claude adapter may not be available — skip silently
			}
		}

		// Send variant info — current thinking level and available variants
		// for the active model (per-session when available, global fallback)
		const currentVariant = activeId
			? overrides.getVariant(activeId)
			: overrides.defaultVariant;
		const activeModelId = activeId
			? overrides.getModel(activeId)?.modelID
			: overrides.defaultModel?.modelID;
		let availableVariants: string[] = [];
		if (activeModelId) {
			for (const p of providers) {
				const model = p.models.find(
					(m: { id: string; variants?: string[] }) => m.id === activeModelId,
				);
				if (model?.variants) {
					availableVariants = model.variants;
					break;
				}
			}
		}
		wsHandler.sendTo(clientId, {
			type: "variant_info",
			variant: currentVariant,
			variants: availableVariants,
		});

src/lib/handlers/model.ts:110

• handleGetModels now includes contextWindowOptions in the model_list payload, but it still doesn’t send any context_window_info message to establish the current selection + options (unlike variant_info). Since the frontend store populates availableContextWindowOptions from context_window_info, the context-window selector won’t become visible after get_models unless something else triggers that message. Suggest sending a context_window_info alongside variant_info using the active model and overrides/default context window.

					models: engineResult.right.models.map((m) => ({
						id: m.id,
						name: m.name,
						provider: "claude",
						...(m.limit ? { limit: m.limit } : {}),
						...(m.variants && Object.keys(m.variants).length > 0
							? { variants: Object.keys(m.variants) }
							: {}),
						...(m.contextWindowOptions && m.contextWindowOptions.length > 0
							? { contextWindowOptions: m.contextWindowOptions }
							: {}),
					})),
				});
				wsHandler.sendTo(clientId, { type: "model_list", providers });
			}

---

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[dibstern]

Also addressed the two suppressed Copilot notes in 91d5f72: client init now sends context_window_info after model_list, and handleGetModels sends the same state using the active model plus the current context-window override/default. Covered by the new unit tests in client-init.test.ts and effect-handlers.test.ts.