Fenced code-block extraction from raw LLM text responses.

Pure parsing. No HTTP, no provider knowledge. Used by `ask-code!` to turn
a plain-text completion into a vector of tagged code blocks the caller
reads/evals directly.

Extraction rules — `extract-code-blocks` recognizes three shapes:
  1. Tagged fence:        ```clojure\n…\n```   →  {:lang "clojure" :source …}
  2. Untagged fence:      ```\n…\n```          →  {:lang nil       :source …}
  3. No fence at all:     entire response          →  {:lang nil       :source …}

`select-blocks` then enforces strict lang matching: ONLY blocks whose
`:lang` equals the caller-supplied target survive. Untagged blocks
(`:lang nil`) — including the fenceless-fallback case — are DROPPED.
Models that want their code accepted MUST tag their fence with the
requested lang.

Wrapper for the JsonishParser Java class.

Provides SAP (Schemaless Adaptive Parsing) for malformed JSON from LLMs.
Handles unquoted keys/values, trailing commas, markdown code blocks, etc.

LLM client layer: HTTP transport, message construction, and all LLM interaction
functions (ask!, abstract!, eval!, refine!, models!, sample!).

models.dev catalog loader.

Reads the bundled `resources/models.dev.json` snapshot (refreshed via
`make refresh-models`) and exposes a normalized view that downstream
router code merges with `KNOWN_PROVIDERS` wire/policy overlay.

Catalog wins for: pricing, context, modalities, capability flags,
release dates, family.
svar overlay wins for: api-style, reasoning-style, llm-headers,
env-keys, base-url, paths, extra-body, exclude-models, rate budgets,
default-models.

Plan-vs-retail pricing — per-provider entries on models.dev already
reflect plan zeros (e.g. `github-copilot`, `zai-coding-plan` ship
{input:0, output:0}). For svar's `:openai-codex` and
`:anthropic-coding-plan` we explicitly want **retail** pricing
(the user pays at API rates once metered), so the overlay declares
`:pricing-source` to redirect catalog lookup to the retail provider.

Router: provider/model registry, circuit breakers, rate limiting, budget tracking,
and routing resolution.

Extracted from defaults.clj (provider/model metadata) and llm.clj (routing logic)
to provide a single cohesive namespace for all routing concerns.

Structured output specification system for LLM responses.

This namespace provides a DSL for defining expected output structures,
converting specs to LLM prompts, and parsing LLM responses back to Clojure data.

Primary functions:
- `field` - Define a field with name, type, cardinality, and description
- `spec` - Create a spec from field definitions
- `build-ref-registry` - Build a registry of referenced specs for nested types
- `spec->prompt` - Generate LLM prompt text from a spec (sent to LLM)
- `str->data` - Parse LLM response string to Clojure data (schemaless)
- `str->data-with-spec` - Parse LLM response with spec-based type coercion
- `validate-data` - Validate parsed data against a spec
- `data->str` - Serialize Clojure data to JSON string

Data Flow:
1. Define spec with `spec` and `field` functions
2. Generate prompt with `spec->prompt` (sent to LLM)
3. Parse response with `str->data-with-spec` (LLM response -> typed Clojure map)
4. Optionally validate with `validate-data`
5. Optionally serialize with `data->str`

Canonical token-usage shape — single source of truth across providers.

Phase A of svar 0.6.0. Replaces the hybrid pre-0.6 shape that emitted
`:prompt_tokens` with provider-dependent semantics (Anthropic
additive, OpenAI inclusive) under the same key. Every provider
normalizer now produces the SAME shape; downstream consumers read
one set of keys regardless of which model served the call.

Canonical shape — INVARIANT: `regular + cache-write + cache-read = input-tokens`:

  {:input-tokens          <long>   ;; TOTAL prompt tokens (always inclusive)
   :output-tokens         <long>   ;; TOTAL completion tokens
   :input-tokens-details  {:regular     <long>   ;; not from cache, not written
                           :cache-write <long>   ;; written this request (1.25× input rate, anthropic; 0 else)
                           :cache-read  <long>}  ;; served from cache (0.1× input rate, anthropic; ~10-50% off, openai)
   :output-tokens-details {:reasoning   <long>}  ;; subset of output-tokens
   :total-tokens          <long>   ;; convenience = input-tokens + output-tokens
   :raw                   <map>}   ;; original provider envelope (debug / forensics)

Provider differences:

- Anthropic Messages API (`:anthropic` api-style): RAW
  `input_tokens` excludes cached AND cache-creation. Canonical
  `:input-tokens` adds all three so the value is TOTAL.

- OpenAI Chat / Responses (`:openai-compatible-*` api-styles): RAW
  `prompt_tokens` / `input_tokens` IS the total. Cached subset lives
  under `prompt_tokens_details.cached_tokens` /
  `input_tokens_details.cached_tokens`. No native `cache-write`
  concept (server-managed implicit caching), so `:cache-write` is
  always 0 here UNLESS the provider proxies Anthropic via OpenRouter
  and surfaces `cache_creation_input_tokens` as a pydantic extra
  field.

- Z.ai (GLM coding-plan / OpenAI-compatible-chat): same as OpenAI.

Industry alignment (May 2026):

- Vercel AI SDK V3 spec (vercel/ai#9921): `inputTokens` always TOTAL
  with `inputTokensDetails {regular, cacheWrite, cacheRead}`.
- OpenTelemetry `gen_ai.usage.input_tokens` (≥ v1.37): SHOULD be
  inclusive (all kinds of input tokens).
- Claude Code official statusline JSON:
  `context_window.total_input_tokens = input + cache_creation + cache_read`.

Reject: the additive convention (e.g. litellm PR #23342) leaves
`total_tokens` inconsistent with `prompt_tokens` and breaks naive
aggregation downstream.

Shared internal utilities.