fix(web-ui): scope task model picker changes per task

[oshea-patrick]

Summary

Closes #469.

When task-level Cline settings partially override the workspace defaults, the task detail model picker can initialize or persist the wrong model. This PR fixes two related bugs:

1. A task with a provider override but no explicit model could initialize from the global Cline model instead of the overridden provider's default model
2. Changing the model from an existing task chat/detail panel could write to workspace-global Cline settings instead of materializing a task-specific override

Changes

• Provider-default model resolution: getInitialTaskModelId now consults the provider catalog to resolve the correct default model when a task overrides providerId but not modelId
• Task-scoped persistence: The detail-panel model picker now writes task-level overrides even when the task was previously inheriting defaults (onTaskClineSettingsChanged presence is sufficient)
• Board mutation: applyTaskDetailClineSettingsChange no longer requires pre-existing explicit task settings to materialize a concrete override
• Dirty-state fix: hasUnsavedChanges now compares effective model selections (resolving blanks to provider defaults) so async catalog loading does not transiently flip the settings UI into an unsaved state

Tests Added

• Provider-default model resolution when taskClineSettings has providerId but no modelId
• No transient hasUnsavedChanges flash during async provider catalog loading
• Task model override materialization for inherited tasks via the chat picker
• Cross-task provider/model isolation in board state mutations
• Sequential task start payloads carry their own clineSettings
• Detail-panel model persistence routes to task callback vs workspace save

Validation

cd web-ui
NODE_OPTIONS=--max-old-space-size=8192 ./node_modules/.bin/vitest run \
  src/state/board-state.test.ts \
  src/hooks/use-task-sessions.test.tsx \
  src/components/detail-panels/cline-agent-chat-panel.model-persistence.test.tsx \
  src/hooks/use-runtime-settings-cline-controller.test.tsx \
  --maxWorkers=1
# 63 tests passed

[greptile-apps]

Greptile Summary

This PR fixes two related bugs in the task-level model picker: a task overriding only providerId could initialize from the wrong (global) model, and saving a model change from a detail panel without pre-existing task settings could write to workspace-wide config instead of the task. The fix is well-structured and covered by a thorough test suite (63 tests across 4 files).

• Provider-default resolution (getInitialTaskModelId): When taskClineSettings has providerId but no modelId, the hook now consults the async provider catalog to derive the correct default, with getComparableModelId used in hasUnsavedChanges to avoid a transient dirty-state flash while the catalog is loading.
• Task-scoped persistence (shouldPersistTaskClineSettings): The detail-panel model picker now routes to the task callback whenever onTaskClineSettingsChanged is provided — not only when the task already had explicit Cline settings — and applyTaskDetailClineSettingsChange in board state no longer gates on a pre-existing explicit agent setting, so an inherited task can have its first concrete override materialized correctly.

Confidence Score: 5/5

Safe to merge — all changed paths are covered by dedicated tests and the logic correctly scopes model changes to the intended task.

The three changed behaviours (provider-default model resolution, task-scoped persistence routing, and board-state override materialization) each have direct test coverage. The async catalog-loading race that previously caused a transient dirty state is resolved by comparing effective model IDs rather than raw state values, and the test with a deferred catalog promise explicitly verifies no intermediate dirty snapshot occurs. No pre-existing guards are weakened in ways that could affect unrelated code paths.

No files require special attention.

Important Files Changed

Filename	Overview
web-ui/src/hooks/use-runtime-settings-cline-controller.ts	Adds getInitialTaskModelId, getComparableModelId, and getResetModelId helpers; hasUnsavedChanges now compares effective model IDs to prevent transient dirty-state during async catalog load
web-ui/src/state/board-state.ts	applyTaskDetailClineSettingsChange no longer requires pre-existing explicit agent settings and now calls updateTask directly, correctly materializing task overrides for inherited tasks
web-ui/src/components/detail-panels/cline-agent-chat-panel.tsx	shouldPersistTaskClineSettings now includes the onTaskClineSettingsChanged !== undefined condition so detail-panel model changes always route to the task callback when one exists
web-ui/src/components/detail-panels/cline-agent-chat-panel.model-persistence.test.tsx	New test file covering task-callback routing vs workspace-save fallback for detail-panel model selection
web-ui/src/hooks/use-runtime-settings-cline-controller.test.tsx	Adds two tests: provider-default model resolution for task overrides with only providerId, and no transient hasUnsavedChanges flash during deferred catalog load
web-ui/src/hooks/use-task-sessions.test.tsx	Adds cross-task provider/model isolation test; refactors mock to be task-specific via mockImplementation
web-ui/src/state/board-state.test.ts	Adds tests for inherited-task materialization and cross-task isolation in board state mutations

_{Reviews (2): Last reviewed commit: "fix(web-ui): keep task model picker chan..." | Re-trigger Greptile}