fix(oauth): preserve primary cache fallback

[steipete]

Summary

• preserve the established priority of an explicit tokenCacheDir when the lower-priority shared OAuth vault is unreadable
• retain successful secondary-store snapshots for generation-aware rejected-credential recovery
• add regression coverage for both cached tokens and cached client information

Root cause

The rejected-refresh recovery landed in 85f4c9e changed composite token and client reads from ordered fallback to Promise.all. A lower-priority vault read error could therefore invalidate a usable explicit cache.

Proof

• pnpm exec vitest run tests/oauth-persistence.test.ts tests/runtime-transport.test.ts — 73 passed
• pnpm check && pnpm test — formatting, lint, typecheck, and build clean; 833 passed, 3 skipped
• autoreview: no accepted/actionable findings remain; a proposed lower-priority write-tolerance expansion was rejected as pre-existing behavior outside this regression's scope
• Public Model Identifier Gate: PASS; no model identifiers or model-bearing artifacts in the candidate diff or proof
• authenticated live Notion proof explicitly waived for refreshable_bearer: refresh failure path lacks invalid_grant/concurrent-refresh recovery — stale rotated refresh token replayed until provider revokes the grant (Notion MCP) #226 and commit dcb683fb959a011dacf1ef80e04eb63289750bf9; deterministic rotating-token E2E and repository tests accepted for landing

Related: #226

[steipete]

Land-ready proof for exact head dcb683fb959a011dacf1ef80e04eb63289750bf9:

• focused OAuth/runtime regressions: 73 passed
• full repository gate: format, lint, typecheck, and build clean; 833 passed, 3 skipped
• autoreview: no accepted/actionable findings remain within the rejected-refresh recovery scope
• Ubuntu CI: https://github.com/openclaw/mcporter/actions/runs/29162437661/job/86569696835
• macOS CI: https://github.com/openclaw/mcporter/actions/runs/29162437661/job/86569696865
• Windows CI: https://github.com/openclaw/mcporter/actions/runs/29162437661/job/86569696836
• Public Model Identifier Gate: PASS; candidate and proof contain no model identifiers or model-bearing artifacts
• authenticated live Notion proof was explicitly waived for refreshable_bearer: refresh failure path lacks invalid_grant/concurrent-refresh recovery — stale rotated refresh token replayed until provider revokes the grant (Notion MCP) #226 and this candidate; deterministic rotating-token E2E and repository tests were accepted for landing

Risk: medium. The change touches OAuth persistence priority and recovery snapshots, with a focused unreadable-secondary-store regression covering tokens and client information.