Four labeled-scope mismatches in cost/cache displays, bundled as the
tail of the cost-display cleanup line (esengine#6075 fixed the big one):

- Desktop status bar 平均命中 silently switched scope: the live value
  used the wire session counters (executor agent only) while the
  fallback used tab telemetry (all request sources). Prefer the
  all-sources telemetry — matching the 会话费用 tooltip's "includes
  main model, subagents and auxiliary calls" — with the executor-only
  live counters only bridging a fresh session's first turn.
- CLI status line painted "turn hit 0.00%" for providers that report
  no prompt-cache fields, by falling back to PromptTokens as the
  denominator. The tag now hides when cache fields are absent; a
  genuine full miss (fields present, hit zero) still renders.
- serve web UI "总费用" accumulated since page load across session
  rotations and fell back to a single request's cost. The counters now
  reset on /new and /resume, the single-request fallback is gone, and
  the card is relabeled 会话费用/Session Cost.
- Desktop ContextPanel's session-cost fallback chain could render one
  request's usage.cost under the 会话费用 label; single-request
  branches removed (usage now contributes currency only).

…es scope

Review catch on this PR: the panel's session cache average still
preferred usage.sessionCacheHitTokens — the wire session counters the
Go agent scopes to the executor only — over the all-sources telemetry,
while the same panel's session cost and per-source rows (and StatusBar
after this PR) already report all sources. Because the reducer keeps
s.usage across context refreshes, the executor-only number would stick
indefinitely.

Extract contextSessionCache: panel info first, ContextInfo second, wire
counters only as the pre-refresh bridge for a fresh session — and pick
hit/miss as a pair from a single source so the computed rate can never
mix scopes (the old per-field ?? chains could).