fix(core/webview): merge view-local state into getState for per-view overrides

[easonLiangWorldedtech]

Part of the vps2 durable per-view state series — tracked in easonLiangWorldedtech#41 (cross-repo: standalone a+d measured against the stack base; the displayed vs-main diff includes F1a #1546 until it merges).

Issue (created at PR-open time): #1549

What

Fix unit F1b (2/3 of the F1 split). F1a landed the per-view identity, the durable viewStates pipeline, and the in-memory viewLocalState buffer, but getState() still read every field straight from the shared ContextProxy — so a webview reporting state ignored its own hydrated per-view selections. This PR merges viewLocalState on top of the context values in getState() and ports the getState merging + local state isolation spec coverage from the superseded vps2 source. It also pins the full default surface of the merged read path (mutation-diff gate). The webview-side identity / launch wiring (F1c) lands in the follow-up.

Design decisions

• getState() builds mergedStateValues = { ...contextProxy.getValues(), ...viewLocalState } and serves every per-view-capable field off the merge: a view-local selection always beats the shared global value; unset fields fall back to the shared value with the existing defaults untouched.
• apiConfiguration is the merged object { ...providerSettings, ...mergedStateValues.apiConfiguration } — the flat provider-settings mutation path (F1a) keeps repopulating the buffer field, so the re-merge at read time stays coherent (parked item 7, documented).
• mode / modeApiConfigs read from the merge with the existing defaults (?? defaultModeSlug / ?? {}); no new validation at the read path — unknown modes are already dropped at write time by F1a's setValues / setValue validation.
• The read path stays side-effect free: getState() never writes, so no queue / rekey behavior is introduced here.

Measurements

• a+d vs stack base F1a head 0a8ffc9e1: 717 (622+/95−) — over the 400 soft budget (spec-heavy unit: 518 of the added lines are the new spec describes); under the 1000 hard cap. Measured git diff --numstat 0a8ffc9e1..HEAD.
• src executable lines (mutation preflight): ClineProvider.ts 104+/95−, confined to the getState() region — under the 500-line cap; the spec file is test-only.

Gates

• eslint --prune-suppressions: pass (suppression counts unchanged: ClineProvider.ts no-explicit-any 12; ClineProvider.spec.ts 198; prune-only reindent reverted)
• check-types: pass
• prettier: both files stable
• vitest: ClineProvider.spec.ts 206 pass (185 pre-existing + 17 ported + 4 new default-value tests)
• stryker-diff ci @ 0a8ffc9: pass — 127/127 mutants killed (0 Survived, 0 NoCoverage; under the 400-mutant and 500-executable-line caps)
• e2e / i18n / visual: n/a (zero new i18n strings; no webview-ui changes)

Parked / documented

From the gap-review parked-items register (F1b scope, all bounded):

1. Flat-mutation apiConfiguration replace (item 7) — a flat setValues provider-settings write replaces the buffer apiConfiguration object; coherent via the getState() re-merge introduced here.
2. Editor-tab viewStates orphan after window reload (item 8) — no panel serializer; prune-bounded. No change in this unit.

Porting notes

• Ported hunk-by-hunk (re-implemented against this base from the fix(webview): add durable per-view state base #977 source of record e9a44b2): ClineProvider.ts h17 (the mergedStateValues merge in getState()) + h18 (the full getState() return block: ~85 field reads switched from stateValues.* to mergedStateValues.*, the apiConfiguration object merge, the mode / modeApiConfigs defaults). The getState() method region verified identical to the source of record line-for-line (198 lines).
• Spec port: local state isolation describe (2 tests) + getState merging describe (15 tests) from the CS ClineProvider.parallelMode.spec.ts, adapted to this file's fixture: the file-level getModeBySlug mock resolves every slug, so the unknown-mode test narrows the mock per-test (same try/finally pattern as F1a); that test's first assertion targets the empty proxy cache (toBeUndefined()) instead of the CS fixture's seeded global default.
• Gate-driven addition (not in CS): getState default values describe (4 tests) — the mutation-diff gate requires every changed-code mutant killed, so the merged read path's ~45 default-fallback lines are pinned to their defaults (including the codebaseIndexModels fallback, which is only observable after clearing the value the constructor seeds into the context — with a truthy stored value the ?? and && forms of the line are indistinguishable), plus the apiProvider fill-in is exercised through a non-retired provider and through a value that ContextProxy sanitizes away (the only path where the ternary's retired check is observable in the returned apiConfiguration).
• CS hunks intentionally NOT ported (register in the tracking issue, observed by this PR as well): all six register entries (kimi-code OAuth try/catch, ApiConfigManager className tweak, visual.tsx deletion + baselines, mojibake comment, unused defaultModeSlug import — lands with F1c/F3, repo-config churn).

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[codecov]

Codecov Report

❌ Patch coverage is 98.36066% with 4 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/core/webview/ClineProvider.ts	98.00%	0 Missing and 4 partials ⚠️

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