[Copilot]

This updates the Chapter 8 companion files so pricing stays JSON-driven, token routing/budget examples are covered by deterministic offline tests, and the Prometheus dashboard artifacts are validated in CI. It also reconciles Chapter 8 path references with the repository’s nested layout.

• Pricing source of truth

  • Refreshes chapters/ch08/pricing.json metadata for the retrieval date and clarifies that live Anthropic pricing could not be re-verified from the sandbox due to unreachable public hosts.
  • Keeps Table 8.1 pricing flow JSON-driven via PRICING_PATH/table_8_1_rates() with no separate hardcoded rate table.
  • Fixes Chapter 8 companion-file path comments to match the actual repo layout.

• Model router coverage

  • Expands Chapter 8 unit coverage for count_tokens, route_model, and cost_estimate_usd.
  • Asserts offline/local token fallback behavior, provider-failure fallback, small-vs-large routing thresholds, force_large=True, and that the chapter-opening cost figure matches both pricing.json and cost_estimate_usd().

• Token budget management (Listing 8.2)

  • Refines chapters/ch08/token_budget.py around an explicit budgeted context shape that includes question.
  • Keeps retrieval trimming first, then history summarization via deterministic MockProvider behavior, and raises when the context still cannot fit.
  • Adds tests for trim-only, trim-then-summarize, and failure paths.

• Prometheus dashboard artifacts (Listing 8.3)

  • Renames the rules file to chapters/ch08/dashboard_rules.yml.
  • Defines llm_token_price_usd_per_mtok as per-model, per-price-type constant recording rules sourced from the same values as pricing.json.
  • Updates dashboard_queries.promql to include commented Chapter 8 cost queries and restores the / 1e6 conversion so token-rate × USD-per-million-token math stays dimensionally correct.

• CI / parser validation

  • Adds chapters/ch08/verify_promql.sh to validate both the rules file and each PromQL expression through promtool.
  • Wires validation into the existing CI workflow and adds a focused root-level Chapter 8 workflow with explicit contents: read permissions.
  • Unignores the verifier script so it can be tracked in the repo.

Example of the updated pricing join pattern:

sum by (model) (
  (label_replace(
    rate(gen_ai_client_token_usage_total{token_type=~"input|cached_input|output"}[5m]),
    "price_type", "$1", "token_type", "(.*)"
  ) / 1e6)
  * on (model, price_type) group_left
  llm_token_price_usd_per_mtok
)