anthropic prompt caching

1 files changed, 73 insertions, 1 deletions

diff --git a/src/config_file.zig b/src/config_file.zig
index f5ed79c..1858520 100644
--- a/src/config_file.zig
+++ b/src/config_file.zig
@@ -25,7 +25,10 @@
 //!     by `api_key_env_var`. A provider whose only key source is an absent
 //!     env var is **silently dropped** — this is what lets the base layer
 //!     ship default OpenAI/Anthropic providers that simply don't appear when
-//!     the user hasn't exported the corresponding key.
+//!     the user hasn't exported the corresponding key. An `anthropic_messages`
+//!     provider may also set `prompt_cache = <bool>` (default true) to control
+//!     the advancing `cache_control` breakpoint; it is ignored for
+//!     `openai_chat` providers.
 //!   - `defaults.model` is parsed as `<provider_name>:<model_alias>`.
 //!   - `tools` / `extensions` allow- and deny-lists are captured verbatim
 //!     (as glob pattern lists). A pattern appearing in both allow and deny
@@ -67,6 +70,10 @@ pub const Provider = struct {
     style: APIStyle,
     base_url: []const u8,
     api_key: []const u8,
+    /// anthropic_messages only. Place one advancing `cache_control`
+    /// breakpoint on each request. Defaults to the library default (true);
+    /// ignored for `openai_chat` providers.
+    prompt_cache: bool = true,
 
     pub fn deinit(self: Provider, alloc: Allocator) void {
         alloc.free(self.name);
@@ -150,6 +157,7 @@ pub fn buildProviderConfig(
             .effort = if (def_opt) |d| d.effort else .medium,
             .thinking_budget_tokens = if (def_opt) |d| d.thinking_budget_tokens else 32_000,
             .thinking_interleaved = if (def_opt) |d| d.thinking_interleaved else false,
+            .prompt_cache = prov.prompt_cache,
         } },
     }
 }
@@ -545,11 +553,20 @@ fn resolveProvider(
         return null;
     };
 
+    // anthropic_messages only; absent => library default (true).
+    const prompt_cache: bool = blk: {
+        if (val.get("prompt_cache")) |pc| {
+            if (pc.asBool()) |b| break :blk b;
+        }
+        break :blk true;
+    };
+
     return .{
         .name = try allocator.dupe(u8, name),
         .style = style,
         .base_url = try allocator.dupe(u8, base_url),
         .api_key = try allocator.dupe(u8, api_key),
+        .prompt_cache = prompt_cache,
     };
 }
 
@@ -732,6 +749,61 @@ test "resolve: env-backed provider resolves when env var is set" {
     try testing.expectEqualStrings("sk-ant-xyz", p.api_key);
 }
 
+test "resolve: prompt_cache defaults true and is parsed when set" {
+    const a = testing.allocator;
+    var env = emptyEnv(a);
+    defer env.deinit();
+
+    const src =
+        \\[providers.anthropic]
+        \\style = "anthropic_messages"
+        \\base_url = "https://api.anthropic.com"
+        \\api_key = "sk-ant"
+        \\
+        \\[providers.anthropic_nocache]
+        \\style = "anthropic_messages"
+        \\base_url = "https://api.anthropic.com"
+        \\api_key = "sk-ant"
+        \\prompt_cache = false
+    ;
+    const doc = try parseDoc(a, src);
+    defer doc.deinit();
+
+    var cfg = try resolve(a, &env, doc.root);
+    defer cfg.deinit();
+
+    // Absent => library default (true).
+    try testing.expectEqual(true, cfg.provider("anthropic").?.prompt_cache);
+    // Explicit false is honoured.
+    try testing.expectEqual(false, cfg.provider("anthropic_nocache").?.prompt_cache);
+}
+
+test "buildProviderConfig: prompt_cache flows from provider into anthropic config" {
+    const a = testing.allocator;
+    var env = emptyEnv(a);
+    defer env.deinit();
+
+    const src =
+        \\[providers.anthropic]
+        \\style = "anthropic_messages"
+        \\base_url = "https://api.anthropic.com"
+        \\api_key = "sk-ant"
+        \\prompt_cache = false
+    ;
+    const doc = try parseDoc(a, src);
+    defer doc.deinit();
+
+    var cfg = try resolve(a, &env, doc.root);
+    defer cfg.deinit();
+
+    var defs = models_toml.ModelRegistry.init(a);
+    defer defs.deinit();
+
+    const pc = try buildProviderConfig(&cfg, &defs, .{ .provider = "anthropic", .model = "sonnet" });
+    try testing.expectEqual(APIStyle.anthropic_messages, pc.style());
+    try testing.expectEqual(false, pc.anthropic_messages.prompt_cache);
+}
+
 test "resolve: inline api_key wins over env var" {
     const a = testing.allocator;
     var env = emptyEnv(a);