feat(kilo-auto-model): add input_cache_read and input_cache_write prices (#1638)

## Summary

Adds `input_cache_read_price` and `input_cache_write_price` fields to
the `AutoModel` type and populates them for all four Kilo Auto models.
Prices are sourced from OpenRouter (`/api/v1/models`) using the most
expensive constituent model in each tier:

- **Frontier** (`anthropic/claude-opus-4.6`): cache_read `0.0000005`,
cache_write `0.00000625`
- **Balanced** (`moonshotai/kimi-k2.5`): cache_read `0.000000225`,
cache_write undefined (not offered)
- **Small** (`openai/gpt-5-nano`): cache_read `0.000000005`, cache_write
undefined (not offered)
- **Free**: cache_read `0`, cache_write `0`

The `buildAutoModels()` function in `openrouter/index.ts` is updated to
pass `input_cache_read` and `input_cache_write` through to the `pricing`
object in the model response, which already supports these optional
fields via the Zod schema in `organization-types.ts`.

## Verification

- Reviewed OpenRouter API response for all constituent model IDs to
confirm prices
- Verified `OpenRouterModel.pricing` Zod schema accepts `string |
undefined` for both cache fields
- Confirmed field names match the existing `input_cache_read` /
`input_cache_write` convention used elsewhere in the codebase

## Visual Changes

N/A

## Reviewer Notes

Cache write prices are `undefined` for Balanced and Small because those
constituent models (`kimi-k2.5`, `gpt-5-nano`) do not offer a cache
write price on OpenRouter. The Frontier model uses Claude Opus 4.6
pricing since it is the most expensive model routed to in that tier.

Author: chrarnoldus

src/lib/kilo-auto-model.ts

@@ -32,6 +32,8 @@ type AutoModel = {
   max_completion_tokens: number;
   prompt_price: string;
   completion_price: string;
+  input_cache_read_price: string | undefined;
+  input_cache_write_price: string | undefined;
   supports_images: boolean;
   roocode_settings: ModelSettings | undefined;
   opencode_settings: OpenCodeSettings | undefined;
@@ -130,6 +132,8 @@ export const KILO_AUTO_FRONTIER_MODEL: AutoModel = {
   max_completion_tokens: 128_000,
   prompt_price: '0.000005',
   completion_price: '0.000025',
+  input_cache_read_price: '0.0000005',
+  input_cache_write_price: '0.00000625',
   supports_images: true,
   roocode_settings: undefined,
   opencode_settings: {
@@ -146,6 +150,8 @@ export const KILO_AUTO_FREE_MODEL: AutoModel = {
   max_completion_tokens: mimo_v2_pro_free_model.max_completion_tokens,
   prompt_price: '0',
   completion_price: '0',
+  input_cache_read_price: '0',
+  input_cache_write_price: '0',
   supports_images: false,
   roocode_settings: {
     included_tools: ['search_and_replace'],
@@ -162,6 +168,8 @@ export const KILO_AUTO_BALANCED_MODEL: AutoModel = {
   max_completion_tokens: 131072,
   prompt_price: '0.0000006',
   completion_price: '0.000003',
+  input_cache_read_price: '0.000000225',
+  input_cache_write_price: undefined,
   supports_images: true,
   roocode_settings: {
     included_tools: ['edit_file'],
@@ -178,6 +186,8 @@ export const KILO_AUTO_SMALL_MODEL: AutoModel = {
   max_completion_tokens: 32768,
   prompt_price: '0.00000005',
   completion_price: '0.0000004',
+  input_cache_read_price: '0.000000005',
+  input_cache_write_price: undefined,
   supports_images: false,
   roocode_settings: undefined,
   opencode_settings: undefined,

src/lib/providers/openrouter/index.ts

@@ -38,6 +38,8 @@ function buildAutoModels(): OpenRouterModel[] {
     pricing: {
       prompt: m.prompt_price,
       completion: m.completion_price,
+      input_cache_read: m.input_cache_read_price,
+      input_cache_write: m.input_cache_write_price,
       request: '0',
       image: '0',
       web_search: '0',

src/tests/openrouter-models-sorting.approved.json

@@ -23,6 +23,8 @@
       "pricing": {
         "prompt": "0.000005",
         "completion": "0.000025",
+        "input_cache_read": "0.0000005",
+        "input_cache_write": "0.00000625",
         "request": "0",
         "image": "0",
         "web_search": "0",
@@ -66,6 +68,7 @@
       "pricing": {
         "prompt": "0.0000006",
         "completion": "0.000003",
+        "input_cache_read": "0.000000225",
         "request": "0",
         "image": "0",
         "web_search": "0",
@@ -113,6 +116,8 @@
       "pricing": {
         "prompt": "0",
         "completion": "0",
+        "input_cache_read": "0",
+        "input_cache_write": "0",
         "request": "0",
         "image": "0",
         "web_search": "0",
@@ -710,6 +715,7 @@
       "pricing": {
         "prompt": "0.00000005",
         "completion": "0.0000004",
+        "input_cache_read": "0.000000005",
         "request": "0",
         "image": "0",
         "web_search": "0",