fix(usage): preserve nonnegative provider-reported exact cost

[ryanngit]

Summary

Preserve trusted provider-reported exact request cost without replacing current pricing tables or usage UI.

• carry cost_usd, cost_in_usd, and cost_in_usd_ticks through usage extraction, normalization, format filtering, and canonical storage
• prefer cost_usd, then cost_in_usd, then xAI ticks
• accept finite nonnegative totals, including exact zero
• reject negative, empty, NaN, and infinite totals
• trust exact provider total even when local model pricing is missing
• convert xAI ticks using 1 USD = 10^10 ticks
• fall back to current local token pricing when exact value is invalid or absent

Scope

This refresh intentionally excludes:

• model pricing table changes
• cache-write/effective-tier transport
• stored/UI component breakdowns
• xAI local quota/dashboard rows
• historical usage rewrites
• API-key grouping

Streaming cache/tier work remains separate and overlaps #2348, #2713, #2747, #2873, and #2880. Exact embedding usage from #2794 is already upstream.

Base: v0.5.45 at 6fcd27337a7893642c7fe630840d0a641743f28f

Verification

• focused/adjacent Vitest: 2 files, 25/25 passed
• tests cover missing pricing, exact zero, precedence, negative rejection, xAI tick scale, streaming extraction, non-streaming extraction, and existing cache accounting
• production npm run build: passed
• changed-file ESLint: passed
• git diff --check: passed
• Gitleaks: 4 changed files, no findings

Full upstream suite is not used as binary gate because pristine v0.5.45 currently has 111 unrelated baseline failures.

Updated onto v0.5.35. Conflict resolution preserves upstream concise request logging while retaining service-tier attribution and exact cache/cost accounting. Focused pricing/usage tests pass (33/33); changed-path lint differs only by the same four React findings present on stock v0.5.35.

v0.5.40 refresh

• Base: upstream/master = v0.5.40 (79918c7)
• Branch head: 2a6741b7f10793db784c21a9fc20993447536b36 (was bf2da7259601f839207c1bb9d4bdcfb3e09017c4)
• Merge: merged
• Tests (TMPDIR in worktree): pass — Test Files 5 passed (5); Tests 31 passed (31);
• Files: tests/unit/xai-usage.test.js tests/unit/current-model-pricing.test.js tests/unit/responses-stream-to-json-usage.test.js tests/unit/usage-dispatch.test.js tests/unit/cached-token-usage.test.js
• git diff --check: clean
• gitleaks on range: ok

v0.5.45 split refresh

Force-pushed 846b0d2f from pristine v0.5.45, replacing old combined history with one exact-total commit.

Corrected old branch defects:

• exact cost now wins when pricing is null
• negative exact totals are rejected
• zero remains authoritative
• xAI scale is 1e10 ticks per USD, not 1e12

Removed pricing tables, cache/tier transport, UI breakdown, xAI local usage, and already-merged embedding scope. Fresh gates: 25/25 tests, production build, ESLint, diff check, and Gitleaks passed.