//! Anthropic Messages API JSON serialization and event parsing.
//!
//! Two responsibilities:
//!   1. Serialize a `Conversation` into a `/v1/messages` request body.
//!      Anthropic differs from OpenAI in several ways — see `serializeRequest`.
//!   2. Parse one streaming SSE event payload (the JSON object after `data: `)
//!      into a strongly-typed `StreamEvent` that the provider can consume.
//!
//! Wire format reference:
//!   https://platform.claude.com/docs/en/build-with-claude/streaming
//!   https://platform.claude.com/docs/en/build-with-claude/extended-thinking

const std = @import("std");
const Allocator = std.mem.Allocator;
const Writer = std.Io.Writer;
const conversation = @import("conversation.zig");
const config_mod = @import("config.zig");
const tool_registry_mod = @import("tool_registry.zig");

// -----------------------------------------------------------------------------
// Request serialization
// -----------------------------------------------------------------------------

/// Serialize a Conversation into a `/v1/messages` request body.
///
/// Differences from OpenAI Chat Completions:
///   - System messages are extracted and concatenated into a top-level
///     `system` string. They do not appear in the `messages` array.
///   - `content` is always an array of typed blocks, never a bare string.
///   - `max_tokens` is required.
///
/// Caller owns the returned slice.
pub fn serializeRequest(
    allocator: Allocator,
    cfg: *const config_mod.AnthropicMessagesConfig,
    conv: *const conversation.Conversation,
    tools: *const tool_registry_mod.ToolRegistry,
) ![]u8 {
    var aw: Writer.Allocating = .init(allocator);
    errdefer aw.deinit();

    var s: std.json.Stringify = .{ .writer = &aw.writer };

    try s.beginObject();

    try s.objectField("model");
    try s.write(cfg.model);

    try s.objectField("max_tokens");
    try s.write(cfg.max_tokens);

    try s.objectField("stream");
    try s.write(true);

    // Extended thinking configuration.
    // `.disabled`  — omit the field entirely.
    // `.enabled`   — manual budget: { type, budget_tokens, display }.
    // `.adaptive`  — adaptive mode: { type, display } + output_config.effort.
    switch (cfg.thinking) {
        .disabled => {},
        .enabled => {
            // Resolve budget: explicit value or fall back to max_tokens - 1.
            // Clamp so budget is always strictly less than max_tokens (required
            // by Anthropic when not using interleaved thinking).
            const raw_budget: u32 = cfg.thinking_budget_tokens orelse (cfg.max_tokens -| 1);
            const budget: u32 = if (raw_budget >= cfg.max_tokens) cfg.max_tokens -| 1 else raw_budget;
            try s.objectField("thinking");
            try s.beginObject();
            try s.objectField("type");
            try s.write("enabled");
            try s.objectField("budget_tokens");
            try s.write(budget);
            try s.objectField("display");
            try s.write("summarized");
            try s.endObject();
        },
        .adaptive => {
            try s.objectField("thinking");
            try s.beginObject();
            try s.objectField("type");
            try s.write("adaptive");
            try s.objectField("display");
            try s.write("summarized");
            try s.endObject();
            try s.objectField("output_config");
            try s.beginObject();
            try s.objectField("effort");
            try s.write(@tagName(cfg.effort));
            try s.endObject();
        },
    }

    // Build and emit the concatenated system prompt, if any.
    var system_buf: std.ArrayList(u8) = .empty;
    defer system_buf.deinit(allocator);
    try collectSystemPrompt(conv, &system_buf, allocator);
    if (system_buf.items.len > 0) {
        try s.objectField("system");
        try s.write(system_buf.items);
    }

    if (tools.count() > 0) {
        try s.objectField("tools");
        try s.beginArray();
        var it = tools.toolsForLLM();
        while (it.next()) |t| {
            try s.beginObject();
            try s.objectField("name");
            // `t.decl.name` is already wire-encoded by `toolsForLLM`.
            try s.write(t.decl.name);
            try s.objectField("description");
            try s.write(t.decl.description);
            try s.objectField("input_schema");
            try writeRawJson(&s, t.decl.schema_json);
            try s.endObject();
        }
        try s.endArray();
    }

    // Emit messages (everything that isn't .system). If the conversation
    // has been compacted, only the latest compaction summary and the
    // messages after it are active; the superseded prefix is dropped.
    //
    // Prompt caching: we replicate Anthropic's "automatic caching" by
    // placing one `cache_control` breakpoint on the last cacheable block of
    // the request. Anthropic's native API offers a single top-level
    // `cache_control` field for this, but Anthropic-style proxies
    // (Bedrock, Vertex, OpenRouter) reject that field outright (400). A
    // per-block breakpoint produces the same caching behavior and is the
    // broadly-supported form, so we mark the block directly. As the
    // append-only conversation grows, this breakpoint advances each request
    // and stays well inside the 20-block lookback window, so every turn
    // reads the prior turn's write and writes only its own new suffix.
    const window = conversation.activeMessageWindow(conv.messages.items);
    const cache_at: ?CacheMark = if (cfg.prompt_cache) cacheableTailBlock(window) else null;
    try s.objectField("messages");
    try s.beginArray();
    for (window, 0..) |msg, mi| {
        if (msg.role == .system) continue;
        const mark: ?usize = if (cache_at) |c| (if (c.message == mi) c.block else null) else null;
        try writeMessage(&s, msg, mark, cfg);
    }
    try s.endArray();

    try s.endObject();

    return try aw.toOwnedSlice();
}

/// Splice a pre-encoded JSON value into the current stringifier position.
/// On parse failure, emit `{}` so we never produce invalid wire JSON.
fn writeRawJson(s: *std.json.Stringify, raw: []const u8) !void {
    var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
    defer arena.deinit();
    const parsed = std.json.parseFromSlice(
        std.json.Value,
        arena.allocator(),
        raw,
        .{},
    ) catch {
        try s.beginObject();
        try s.endObject();
        return;
    };
    try s.write(parsed.value);
}

fn writeToolUseInput(s: *std.json.Stringify, raw: []const u8) !void {
    var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
    defer arena.deinit();
    const parsed = std.json.parseFromSlice(std.json.Value, arena.allocator(), raw, .{}) catch {
        try s.beginObject();
        try s.objectField("_invalid_input");
        try s.write(raw);
        try s.endObject();
        return;
    };
    if (parsed.value != .object) {
        try s.beginObject();
        try s.objectField("_invalid_input");
        try s.write(raw);
        try s.endObject();
        return;
    }
    try s.write(parsed.value);
}

/// Build the top-level Anthropic `system` string. Applies the shared
/// append/replace derivation (see `conversation.effectiveSystemBlocks`),
/// strips trailing newlines from each surviving block, and joins them with
/// a horizontal rule (`\n\n---\n\n`). Anthropic's wire format requires a
/// single string, so this rule is its concession to that constraint.
fn collectSystemPrompt(
    conv: *const conversation.Conversation,
    out: *std.ArrayList(u8),
    allocator: Allocator,
) !void {
    var blocks = try conversation.effectiveSystemBlocks(allocator, conv.messages.items);
    defer blocks.deinit(allocator);

    const sep = "\n\n---\n\n";
    var first = true;
    for (blocks.items) |text| {
        const trimmed = std.mem.trimEnd(u8, text, "\n");
        if (!first) try out.appendSlice(allocator, sep);
        try out.appendSlice(allocator, trimmed);
        first = false;
    }
}

/// Location of the prompt-cache breakpoint: the block to stamp with
/// `cache_control`. Indices are into the active message window and into
/// that message's `content` array.
const CacheMark = struct { message: usize, block: usize };

/// Returns whether a content block can carry a `cache_control` marker and
/// is actually emitted on the wire. Thinking blocks can't be cached
/// directly, and unsigned thinking blocks are dropped entirely
/// (`writeBlock` returns early), so neither is a valid breakpoint target.
/// System blocks are filtered before emission.
fn isCacheableBlock(block: conversation.ContentBlock) bool {
    return switch (block) {
        .Text, .ToolUse, .ToolResult, .CompactionSummary => true,
        .Thinking, .System => false,
    };
}

/// Find the last cacheable, actually-emitted block in the active window:
/// the spot to place the single cache breakpoint. Scans messages from the
/// end, skipping system messages and any trailing non-cacheable blocks
/// (e.g. a thinking block as the final assistant block). Returns null if
/// nothing cacheable is present (then no breakpoint is emitted).
fn cacheableTailBlock(window: []const conversation.Message) ?CacheMark {
    var mi = window.len;
    while (mi > 0) {
        mi -= 1;
        const msg = window[mi];
        if (msg.role == .system) continue;
        var bi = msg.content.items.len;
        while (bi > 0) {
            bi -= 1;
            if (isCacheableBlock(msg.content.items[bi])) {
                return .{ .message = mi, .block = bi };
            }
        }
    }
    return null;
}

fn writeMessage(
    s: *std.json.Stringify,
    msg: conversation.Message,
    cache_block: ?usize,
    cfg: *const config_mod.AnthropicMessagesConfig,
) !void {
    try s.beginObject();

    try s.objectField("role");
    try s.write(@tagName(msg.role));

    try s.objectField("content");
    try s.beginArray();
    for (msg.content.items, 0..) |block, bi| {
        const mark = if (cache_block) |cb| cb == bi else false;
        try writeBlock(s, block, mark, cfg, msg.identity);
    }
    try s.endArray();

    try s.endObject();
}

/// Emit a `"cache_control": {"type": "ephemeral"}` field. The caller must
/// be positioned inside an open block object, after its other fields.
fn writeCacheControl(s: *std.json.Stringify) !void {
    try s.objectField("cache_control");
    try s.beginObject();
    try s.objectField("type");
    try s.write("ephemeral");
    try s.endObject();
}

fn writeBlock(
    s: *std.json.Stringify,
    block: conversation.ContentBlock,
    mark_cache: bool,
    cfg: *const config_mod.AnthropicMessagesConfig,
    msg_identity: ?config_mod.WireIdentity,
) !void {
    switch (block) {
        .Text => |tb| {
            try s.beginObject();
            try s.objectField("type");
            try s.write("text");
            try s.objectField("text");
            try s.write(tb.items);
            if (mark_cache) try writeCacheControl(s);
            try s.endObject();
        },
        .Thinking => |tb| {
            // Anthropic requires the signature field to round-trip a thinking
            // block. If we don't have one (e.g. block was synthesized from a
            // non-Anthropic provider), or if the signature came from a
            // different provider/model than the current request, skip the
            // block: Anthropic will reject unsigned thinking on incoming
            // messages, and opaque signatures are not portable across
            // provider/model boundaries.
            const sig = tb.signature orelse return;
            if (!conversation.thinkingSignatureMatches(tb, msg_identity, .anthropic_messages, cfg.base_url, cfg.model)) return;
            try s.beginObject();
            try s.objectField("type");
            try s.write("thinking");
            try s.objectField("thinking");
            try s.write(tb.text.items);
            try s.objectField("signature");
            try s.write(sig);
            try s.endObject();
        },
        .ToolUse => |tu| {
            try s.beginObject();
            try s.objectField("type");
            try s.write("tool_use");
            try s.objectField("id");
            try s.write(tu.id);
            try s.objectField("name");
            // Replayed assistant tool_use: encode the stored dotted name.
            var name_buf: [tool_registry_mod.max_wire_name_len]u8 = undefined;
            try s.write(tool_registry_mod.encodeName(&name_buf, tu.name));
            try s.objectField("input");
            // Anthropic expects `input` as a nested JSON object, not a
            // string. The block's input bytes were assembled from
            // `input_json_delta` fragments — splice them in verbatim.
            // Treat empty as an empty object.
            const input_bytes = tu.input.items;
            if (input_bytes.len == 0) {
                try s.beginObject();
                try s.endObject();
            } else {
                try writeToolUseInput(s, input_bytes);
            }
            if (mark_cache) try writeCacheControl(s);
            try s.endObject();
        },
        .ToolResult => |tr| {
            try s.beginObject();
            try s.objectField("type");
            try s.write("tool_result");
            try s.objectField("tool_use_id");
            try s.write(tr.tool_use_id);
            // Anthropic supports an `is_error` marker on tool results;
            // emit it only when set (omitting it defaults to a success
            // result on the wire).
            if (tr.is_error) {
                try s.objectField("is_error");
                try s.write(true);
            }
            // Anthropic accepts `content` as an array of typed blocks:
            // text, image (base64 source), and document (PDF).
            try s.objectField("content");
            try s.beginArray();
            for (tr.parts.items) |part| {
                switch (part) {
                    .text => |tb| {
                        try s.beginObject();
                        try s.objectField("type");
                        try s.write("text");
                        try s.objectField("text");
                        try s.write(tb.items);
                        try s.endObject();
                    },
                    .media => |m| {
                        const is_pdf = std.mem.eql(u8, m.media_type, "application/pdf");
                        try s.beginObject();
                        try s.objectField("type");
                        try s.write(if (is_pdf) "document" else "image");
                        try s.objectField("source");
                        try s.beginObject();
                        try s.objectField("type");
                        try s.write("base64");
                        try s.objectField("media_type");
                        try s.write(m.media_type);
                        try s.objectField("data");
                        try s.write(m.data.items);
                        try s.endObject();
                        try s.endObject();
                    },
                }
            }
            try s.endArray();
            if (mark_cache) try writeCacheControl(s);
            try s.endObject();
        },
        // System blocks never reach here: `serializeRequest` filters out
        // `.system` messages before emitting the `messages` array, and the
        // system text is hoisted into the top-level `system` string by
        // `collectSystemPrompt`. Present only to keep the switch exhaustive.
        .System => {},
        // A compaction summary is the synthetic seed text standing in for
        // a compacted prefix; the model reads it as ordinary user text.
        .CompactionSummary => |cs| {
            try s.beginObject();
            try s.objectField("type");
            try s.write("text");
            try s.objectField("text");
            try s.write(cs.text.items);
            if (mark_cache) try writeCacheControl(s);
            try s.endObject();
        },
    }
}

// -----------------------------------------------------------------------------
// Streaming event parsing
// -----------------------------------------------------------------------------

/// Parsed shape of one SSE event payload. The `tag` field selects which of
/// the payload variants is populated.
///
/// String slices are borrowed from the underlying `std.json.Parsed`. The
/// caller must keep `parsed` alive (or copy the slices) until the event is
/// fully consumed.
pub const StreamEventTag = enum {
    message_start,
    content_block_start,
    content_block_delta,
    content_block_stop,
    message_delta,
    message_stop,
    ping,
    @"error",
    unknown,
};

pub const ContentBlockKind = enum { text, thinking, tool_use, unknown };

/// Partial token-count snapshot emitted in `message_start` and
/// `message_delta`. Field semantics follow Anthropic's wire format:
///
///   - `input_tokens`: prompt tokens billed at the base rate.
///   - `cache_creation_input_tokens`: prompt tokens written to a new
///     cache entry (1.25× base).
///   - `cache_read_input_tokens`: prompt tokens served from cache
///     (0.1× base).
///   - `output_tokens`: response tokens billed at the output rate.
///
/// `message_start.usage` carries the initial input-side counts (output
/// will be 0 or absent); `message_delta.usage` carries the final
/// `output_tokens` and may repeat the input-side counts. The provider
/// merges them — "missing" means "unchanged," not "reset to zero."
pub const StreamUsage = struct {
    input_tokens: ?u64 = null,
    output_tokens: ?u64 = null,
    cache_creation_input_tokens: ?u64 = null,
    cache_read_input_tokens: ?u64 = null,
};

pub const StreamEvent = union(StreamEventTag) {
    message_start: struct {
        role: ?[]const u8 = null,
        usage: StreamUsage = .{},
    },
    content_block_start: struct {
        index: usize,
        kind: ContentBlockKind,
        // For tool_use blocks (phase 3+):
        tool_id: ?[]const u8 = null,
        tool_name: ?[]const u8 = null,
    },
    content_block_delta: struct {
        index: usize,
        text_delta: ?[]const u8 = null,
        thinking_delta: ?[]const u8 = null,
        signature_delta: ?[]const u8 = null,
        input_json_delta: ?[]const u8 = null,
    },
    content_block_stop: struct {
        index: usize,
    },
    message_delta: struct {
        stop_reason: ?[]const u8 = null,
        usage: StreamUsage = .{},
    },
    message_stop: void,
    ping: void,
    @"error": struct {
        kind: ?[]const u8 = null,
        message: ?[]const u8 = null,
    },
    unknown: void,
};

pub const ParsedStreamEvent = struct {
    parsed: std.json.Parsed(std.json.Value),
    event: StreamEvent,

    pub fn deinit(self: *ParsedStreamEvent) void {
        self.parsed.deinit();
    }
};

pub fn parseStreamEvent(allocator: Allocator, payload: []const u8) !ParsedStreamEvent {
    var parsed = try std.json.parseFromSlice(std.json.Value, allocator, payload, .{});
    errdefer parsed.deinit();

    const root = parsed.value;
    if (root != .object) return .{ .parsed = parsed, .event = .unknown };

    const type_v = root.object.get("type") orelse return .{ .parsed = parsed, .event = .unknown };
    if (type_v != .string) return .{ .parsed = parsed, .event = .unknown };

    const ty = type_v.string;
    if (std.mem.eql(u8, ty, "message_start")) {
        var role: ?[]const u8 = null;
        var usage: StreamUsage = .{};
        if (root.object.get("message")) |m| {
            if (m == .object) {
                if (m.object.get("role")) |r| {
                    if (r == .string) role = r.string;
                }
                if (m.object.get("usage")) |u| {
                    if (u == .object) usage = parseStreamUsage(u.object);
                }
            }
        }
        return .{ .parsed = parsed, .event = .{ .message_start = .{ .role = role, .usage = usage } } };
    }

    if (std.mem.eql(u8, ty, "content_block_start")) {
        const idx = readIndex(root) orelse 0;
        var kind: ContentBlockKind = .unknown;
        var tool_id: ?[]const u8 = null;
        var tool_name: ?[]const u8 = null;
        if (root.object.get("content_block")) |cb| {
            if (cb == .object) {
                if (cb.object.get("type")) |t| {
                    if (t == .string) {
                        if (std.mem.eql(u8, t.string, "text")) {
                            kind = .text;
                        } else if (std.mem.eql(u8, t.string, "thinking")) {
                            kind = .thinking;
                        } else if (std.mem.eql(u8, t.string, "tool_use")) {
                            kind = .tool_use;
                        }
                    }
                }
                if (cb.object.get("id")) |i| {
                    if (i == .string) tool_id = i.string;
                }
                if (cb.object.get("name")) |n| {
                    if (n == .string) tool_name = n.string;
                }
            }
        }
        return .{ .parsed = parsed, .event = .{ .content_block_start = .{
            .index = idx,
            .kind = kind,
            .tool_id = tool_id,
            .tool_name = tool_name,
        } } };
    }

    if (std.mem.eql(u8, ty, "content_block_delta")) {
        const idx = readIndex(root) orelse 0;
        var text_delta: ?[]const u8 = null;
        var thinking_delta: ?[]const u8 = null;
        var signature_delta: ?[]const u8 = null;
        var input_json_delta: ?[]const u8 = null;
        if (root.object.get("delta")) |d| {
            if (d == .object) {
                const dt = blk: {
                    if (d.object.get("type")) |t| {
                        if (t == .string) break :blk t.string;
                    }
                    break :blk "";
                };
                if (std.mem.eql(u8, dt, "text_delta")) {
                    if (d.object.get("text")) |v| if (v == .string) {
                        text_delta = v.string;
                    };
                } else if (std.mem.eql(u8, dt, "thinking_delta")) {
                    if (d.object.get("thinking")) |v| if (v == .string) {
                        thinking_delta = v.string;
                    };
                } else if (std.mem.eql(u8, dt, "signature_delta")) {
                    if (d.object.get("signature")) |v| if (v == .string) {
                        signature_delta = v.string;
                    };
                } else if (std.mem.eql(u8, dt, "input_json_delta")) {
                    if (d.object.get("partial_json")) |v| if (v == .string) {
                        input_json_delta = v.string;
                    };
                }
            }
        }
        return .{ .parsed = parsed, .event = .{ .content_block_delta = .{
            .index = idx,
            .text_delta = text_delta,
            .thinking_delta = thinking_delta,
            .signature_delta = signature_delta,
            .input_json_delta = input_json_delta,
        } } };
    }

    if (std.mem.eql(u8, ty, "content_block_stop")) {
        const idx = readIndex(root) orelse 0;
        return .{ .parsed = parsed, .event = .{ .content_block_stop = .{ .index = idx } } };
    }

    if (std.mem.eql(u8, ty, "message_delta")) {
        var stop_reason: ?[]const u8 = null;
        var usage: StreamUsage = .{};
        if (root.object.get("delta")) |d| {
            if (d == .object) {
                if (d.object.get("stop_reason")) |sr| {
                    if (sr == .string) stop_reason = sr.string;
                }
            }
        }
        // `usage` is on the message_delta event itself, not under `delta`.
        if (root.object.get("usage")) |u| {
            if (u == .object) usage = parseStreamUsage(u.object);
        }
        return .{ .parsed = parsed, .event = .{ .message_delta = .{ .stop_reason = stop_reason, .usage = usage } } };
    }

    if (std.mem.eql(u8, ty, "message_stop")) {
        return .{ .parsed = parsed, .event = .message_stop };
    }

    if (std.mem.eql(u8, ty, "ping")) {
        return .{ .parsed = parsed, .event = .ping };
    }

    if (std.mem.eql(u8, ty, "error")) {
        var kind: ?[]const u8 = null;
        var message: ?[]const u8 = null;
        if (root.object.get("error")) |e| {
            if (e == .object) {
                if (e.object.get("type")) |t| if (t == .string) {
                    kind = t.string;
                };
                if (e.object.get("message")) |m| if (m == .string) {
                    message = m.string;
                };
            }
        }
        return .{ .parsed = parsed, .event = .{ .@"error" = .{ .kind = kind, .message = message } } };
    }

    return .{ .parsed = parsed, .event = .unknown };
}

fn parseStreamUsage(obj: std.json.ObjectMap) StreamUsage {
    return .{
        .input_tokens = readOptionalU64(obj, "input_tokens"),
        .output_tokens = readOptionalU64(obj, "output_tokens"),
        .cache_creation_input_tokens = readOptionalU64(obj, "cache_creation_input_tokens"),
        .cache_read_input_tokens = readOptionalU64(obj, "cache_read_input_tokens"),
    };
}

fn readOptionalU64(obj: std.json.ObjectMap, name: []const u8) ?u64 {
    const v = obj.get(name) orelse return null;
    if (v != .integer) return null;
    if (v.integer < 0) return null;
    return @intCast(v.integer);
}

fn readIndex(root: std.json.Value) ?usize {
    const v = root.object.get("index") orelse return null;
    if (v != .integer) return null;
    if (v.integer < 0) return null;
    return @intCast(v.integer);
}

// -----------------------------------------------------------------------------
// Tests
// -----------------------------------------------------------------------------

const testing = std.testing;

fn testConfig(model: []const u8) config_mod.AnthropicMessagesConfig {
    return .{
        .api_key = "k",
        .base_url = "u",
        .model = model,
        .max_tokens = 1024,
    };
}

/// Test helper: append a single-text user message. `addUserMessage` now
/// takes a block slice (symmetric with `addAssistantMessage`); this wraps
/// the common plain-text case the tests below use.
fn addUserText(conv: *conversation.Conversation, text: []const u8) !void {
    const tb = try conversation.textualBlockFromSlice(conv.allocator, text);
    var block: conversation.ContentBlock = .{ .Text = tb };
    errdefer block.deinit(conv.allocator);
    try conv.addUserMessage(&.{block});
}

test "serializeRequest - system extracted into top-level field" {
    const allocator = testing.allocator;

    var conv = conversation.Conversation.init(allocator);
    defer conv.deinit();

    try conv.addSystemMessage("You are helpful.");
    try addUserText(&conv, "Hello!");

    const cfg = testConfig("claude-sonnet-4-20250514");
    var empty_tools = tool_registry_mod.ToolRegistry.init(allocator);
    defer empty_tools.deinit();
    const body = try serializeRequest(allocator, &cfg, &conv, &empty_tools);
    defer allocator.free(body);

    var parsed = try std.json.parseFromSlice(std.json.Value, allocator, body, .{});
    defer parsed.deinit();

    const root = parsed.value.object;
    try testing.expectEqualStrings("claude-sonnet-4-20250514", root.get("model").?.string);
    try testing.expect(root.get("stream").?.bool);
    try testing.expectEqual(@as(i64, 1024), root.get("max_tokens").?.integer);
    try testing.expectEqualStrings("You are helpful.", root.get("system").?.string);

    // Only the user message appears in `messages`.
    const msgs = root.get("messages").?.array.items;
    try testing.expectEqual(@as(usize, 1), msgs.len);
    try testing.expectEqualStrings("user", msgs[0].object.get("role").?.string);

    // Content is an array of typed blocks, never a bare string.
    const content = msgs[0].object.get("content").?.array.items;
    try testing.expectEqual(@as(usize, 1), content.len);
    try testing.expectEqualStrings("text", content[0].object.get("type").?.string);
    try testing.expectEqualStrings("Hello!", content[0].object.get("text").?.string);
}

test "serializeRequest - prompt_cache marks last block with cache_control" {
    const allocator = testing.allocator;

    var conv = conversation.Conversation.init(allocator);
    defer conv.deinit();
    try addUserText(&conv, "Hi");

    var cfg = testConfig("claude-x");
    cfg.prompt_cache = true;
    var empty_tools = tool_registry_mod.ToolRegistry.init(allocator);
    defer empty_tools.deinit();
    const body = try serializeRequest(allocator, &cfg, &conv, &empty_tools);
    defer allocator.free(body);

    var parsed = try std.json.parseFromSlice(std.json.Value, allocator, body, .{});
    defer parsed.deinit();
    // No top-level field (would break Bedrock/Vertex/OpenRouter).
    try testing.expect(parsed.value.object.get("cache_control") == null);
    // The single user text block carries the breakpoint.
    const block = parsed.value.object.get("messages").?.array.items[0]
        .object.get("content").?.array.items[0].object;
    try testing.expectEqualStrings("ephemeral", block.get("cache_control").?.object.get("type").?.string);
}

test "serializeRequest - cache breakpoint lands on the final block only" {
    const allocator = testing.allocator;

    var conv = conversation.Conversation.init(allocator);
    defer conv.deinit();
    try addUserText(&conv, "first");
    try conv.addAssistantMessage(&.{
        .{ .Text = try conversation.textualBlockFromSlice(allocator, "reply") },
    }, null);
    try addUserText(&conv, "second");

    var cfg = testConfig("claude-x");
    var empty_tools = tool_registry_mod.ToolRegistry.init(allocator);
    defer empty_tools.deinit();
    const body = try serializeRequest(allocator, &cfg, &conv, &empty_tools);
    defer allocator.free(body);

    var parsed = try std.json.parseFromSlice(std.json.Value, allocator, body, .{});
    defer parsed.deinit();
    const msgs = parsed.value.object.get("messages").?.array.items;
    try testing.expectEqual(@as(usize, 3), msgs.len);
    // Only the last message's only block is marked.
    try testing.expect(msgs[0].object.get("content").?.array.items[0].object.get("cache_control") == null);
    try testing.expect(msgs[1].object.get("content").?.array.items[0].object.get("cache_control") == null);
    try testing.expect(msgs[2].object.get("content").?.array.items[0].object.get("cache_control") != null);
}

test "serializeRequest - cache breakpoint skips a trailing thinking block" {
    // A thinking block can't carry cache_control; the breakpoint must fall
    // back to the prior cacheable block (here the assistant text).
    const allocator = testing.allocator;

    var conv = conversation.Conversation.init(allocator);
    defer conv.deinit();

    const sig = try allocator.dupe(u8, "EqQBCgIYAhIM1gbcDa9GJwZA");
    try conv.addAssistantMessage(&.{
        .{ .Text = try conversation.textualBlockFromSlice(allocator, "answer") },
        .{ .Thinking = .{
            .text = try conversation.textualBlockFromSlice(allocator, "trailing thought"),
            .signature = sig,
        } },
    }, null);
    try conversation.setThinkingOrigins(allocator, conv.messages.items[0].content.items, .anthropic_messages, "u", "claude-x");

    var cfg = testConfig("claude-x");
    var empty_tools = tool_registry_mod.ToolRegistry.init(allocator);
    defer empty_tools.deinit();
    const body = try serializeRequest(allocator, &cfg, &conv, &empty_tools);
    defer allocator.free(body);

    var parsed = try std.json.parseFromSlice(std.json.Value, allocator, body, .{});
    defer parsed.deinit();
    const content = parsed.value.object.get("messages").?.array.items[0]
        .object.get("content").?.array.items;
    // text block marked, thinking block not.
    try testing.expectEqualStrings("text", content[0].object.get("type").?.string);
    try testing.expect(content[0].object.get("cache_control") != null);
    try testing.expectEqualStrings("thinking", content[1].object.get("type").?.string);
    try testing.expect(content[1].object.get("cache_control") == null);
}

test "serializeRequest - thinking signature replays from message identity when block origin is absent" {
    // A reloaded thinking block need not carry its own signature_origin: the
    // enclosing message's identity is the per-message source of truth, so a
    // host can rely on it alone (no per-block identity copy required).
    const allocator = testing.allocator;

    var conv = conversation.Conversation.init(allocator);
    defer conv.deinit();
    try conv.addAssistantMessage(&.{
        .{
            .Thinking = .{
                .text = try conversation.textualBlockFromSlice(allocator, "reasoned"),
                .signature = try allocator.dupe(u8, "EqQBCgIYAhIM1gbcDa9GJwZA"),
                // No signature_origin on the block.
            },
        },
        .{ .Text = try conversation.textualBlockFromSlice(allocator, "answer") },
    }, null);
    // Per-message identity matching the request.
    conv.messages.items[0].identity = try conversation.dupeWireIdentity(allocator, .{
        .api_style = .anthropic_messages,
        .base_url = "u",
        .model = "claude-x",
    });

    const cfg = testConfig("claude-x");
    var empty_tools = tool_registry_mod.ToolRegistry.init(allocator);
    defer empty_tools.deinit();
    const body = try serializeRequest(allocator, &cfg, &conv, &empty_tools);
    defer allocator.free(body);

    var parsed = try std.json.parseFromSlice(std.json.Value, allocator, body, .{});
    defer parsed.deinit();
    const content = parsed.value.object.get("messages").?.array.items[0]
        .object.get("content").?.array.items;
    try testing.expectEqualStrings("thinking", content[0].object.get("type").?.string);
    try testing.expectEqualStrings("EqQBCgIYAhIM1gbcDa9GJwZA", content[0].object.get("signature").?.string);
}

test "serializeRequest - thinking dropped when message identity targets a different model" {
    const allocator = testing.allocator;

    var conv = conversation.Conversation.init(allocator);
    defer conv.deinit();
    try conv.addAssistantMessage(&.{
        .{ .Thinking = .{
            .text = try conversation.textualBlockFromSlice(allocator, "reasoned"),
            .signature = try allocator.dupe(u8, "EqQBCgIYAhIM1gbcDa9GJwZA"),
        } },
        .{ .Text = try conversation.textualBlockFromSlice(allocator, "answer") },
    }, null);
    // Identity points at a *different* model than the request.
    conv.messages.items[0].identity = try conversation.dupeWireIdentity(allocator, .{
        .api_style = .anthropic_messages,
        .base_url = "u",
        .model = "some-other-model",
    });

    const cfg = testConfig("claude-x");
    var empty_tools = tool_registry_mod.ToolRegistry.init(allocator);
    defer empty_tools.deinit();
    const body = try serializeRequest(allocator, &cfg, &conv, &empty_tools);
    defer allocator.free(body);

    var parsed = try std.json.parseFromSlice(std.json.Value, allocator, body, .{});
    defer parsed.deinit();
    const content = parsed.value.object.get("messages").?.array.items[0]
        .object.get("content").?.array.items;
    // Only the text block survives; the unportable thinking block is dropped.
    try testing.expectEqual(@as(usize, 1), content.len);
    try testing.expectEqualStrings("text", content[0].object.get("type").?.string);
}

test "serializeRequest - prompt_cache disabled omits all cache_control" {
    const allocator = testing.allocator;

    var conv = conversation.Conversation.init(allocator);
    defer conv.deinit();
    try addUserText(&conv, "Hi");

    var cfg = testConfig("claude-x");
    cfg.prompt_cache = false;
    var empty_tools = tool_registry_mod.ToolRegistry.init(allocator);
    defer empty_tools.deinit();
    const body = try serializeRequest(allocator, &cfg, &conv, &empty_tools);
    defer allocator.free(body);

    var parsed = try std.json.parseFromSlice(std.json.Value, allocator, body, .{});
    defer parsed.deinit();
    try testing.expect(parsed.value.object.get("cache_control") == null);
    const block = parsed.value.object.get("messages").?.array.items[0]
        .object.get("content").?.array.items[0].object;
    try testing.expect(block.get("cache_control") == null);
}

test "serializeRequest - multiple system messages joined with horizontal rule" {
    const allocator = testing.allocator;

    var conv = conversation.Conversation.init(allocator);
    defer conv.deinit();

    try conv.addSystemMessage("Be terse.");
    try conv.addSystemMessage("Be accurate.");
    try addUserText(&conv, "Hi");

    const cfg = testConfig("claude-x");
    var empty_tools = tool_registry_mod.ToolRegistry.init(allocator);
    defer empty_tools.deinit();
    const body = try serializeRequest(allocator, &cfg, &conv, &empty_tools);
    defer allocator.free(body);

    var parsed = try std.json.parseFromSlice(std.json.Value, allocator, body, .{});
    defer parsed.deinit();
    try testing.expectEqualStrings(
        "Be terse.\n\n---\n\nBe accurate.",
        parsed.value.object.get("system").?.string,
    );
}

test "serializeRequest - replace-mode system block wipes prior system text" {
    const allocator = testing.allocator;

    var conv = conversation.Conversation.init(allocator);
    defer conv.deinit();

    try conv.addSystemMessage("original seed");
    try conv.addSystemMessage("original append");
    try conv.replaceSystemMessage("fresh seed");
    try conv.addSystemMessage("fresh append");
    try addUserText(&conv, "Hi");

    const cfg = testConfig("claude-x");
    var empty_tools = tool_registry_mod.ToolRegistry.init(allocator);
    defer empty_tools.deinit();
    const body = try serializeRequest(allocator, &cfg, &conv, &empty_tools);
    defer allocator.free(body);

    var parsed = try std.json.parseFromSlice(std.json.Value, allocator, body, .{});
    defer parsed.deinit();
    try testing.expectEqualStrings(
        "fresh seed\n\n---\n\nfresh append",
        parsed.value.object.get("system").?.string,
    );
}

test "serializeRequest - trailing newlines stripped before the rule join" {
    const allocator = testing.allocator;

    var conv = conversation.Conversation.init(allocator);
    defer conv.deinit();

    try conv.addSystemMessage("line one\n\n");
    try conv.addSystemMessage("line two\n");
    try addUserText(&conv, "Hi");

    const cfg = testConfig("claude-x");
    var empty_tools = tool_registry_mod.ToolRegistry.init(allocator);
    defer empty_tools.deinit();
    const body = try serializeRequest(allocator, &cfg, &conv, &empty_tools);
    defer allocator.free(body);

    var parsed = try std.json.parseFromSlice(std.json.Value, allocator, body, .{});
    defer parsed.deinit();
    try testing.expectEqualStrings(
        "line one\n\n---\n\nline two",
        parsed.value.object.get("system").?.string,
    );
}

test "serializeRequest - no system messages omits the system field" {
    const allocator = testing.allocator;

    var conv = conversation.Conversation.init(allocator);
    defer conv.deinit();
    try addUserText(&conv, "Hi");

    const cfg = testConfig("claude-x");
    var empty_tools = tool_registry_mod.ToolRegistry.init(allocator);
    defer empty_tools.deinit();
    const body = try serializeRequest(allocator, &cfg, &conv, &empty_tools);
    defer allocator.free(body);

    var parsed = try std.json.parseFromSlice(std.json.Value, allocator, body, .{});
    defer parsed.deinit();
    try testing.expect(parsed.value.object.get("system") == null);
}

test "serializeRequest - signed assistant Thinking blocks round-trip" {
    const allocator = testing.allocator;

    var conv = conversation.Conversation.init(allocator);
    defer conv.deinit();

    const sig = try allocator.dupe(u8, "EqQBCgIYAhIM1gbcDa9GJwZA");
    try conv.addAssistantMessage(&.{
        .{ .Thinking = .{
            .text = try conversation.textualBlockFromSlice(allocator, "let me think"),
            .signature = sig,
        } },
        .{ .Text = try conversation.textualBlockFromSlice(allocator, "the answer is 42") },
    }, null);
    try conversation.setThinkingOrigins(allocator, conv.messages.items[0].content.items, .anthropic_messages, "u", "claude-x");

    const cfg = testConfig("claude-x");
    var empty_tools = tool_registry_mod.ToolRegistry.init(allocator);
    defer empty_tools.deinit();
    const body = try serializeRequest(allocator, &cfg, &conv, &empty_tools);
    defer allocator.free(body);

    var parsed = try std.json.parseFromSlice(std.json.Value, allocator, body, .{});
    defer parsed.deinit();

    const msg = parsed.value.object.get("messages").?.array.items[0];
    try testing.expectEqualStrings("assistant", msg.object.get("role").?.string);

    const content = msg.object.get("content").?.array.items;
    try testing.expectEqual(@as(usize, 2), content.len);

    try testing.expectEqualStrings("thinking", content[0].object.get("type").?.string);
    try testing.expectEqualStrings("let me think", content[0].object.get("thinking").?.string);
    try testing.expectEqualStrings(
        "EqQBCgIYAhIM1gbcDa9GJwZA",
        content[0].object.get("signature").?.string,
    );

    try testing.expectEqualStrings("text", content[1].object.get("type").?.string);
    try testing.expectEqualStrings("the answer is 42", content[1].object.get("text").?.string);
}

test "serializeRequest - mismatched thinking origin drops the block" {
    const allocator = testing.allocator;

    var conv = conversation.Conversation.init(allocator);
    defer conv.deinit();

    const sig = try allocator.dupe(u8, "EqQBCgIYAhIM1gbcDa9GJwZA");
    try conv.addAssistantMessage(&.{
        .{ .Thinking = .{
            .text = try conversation.textualBlockFromSlice(allocator, "other provider thinking"),
            .signature = sig,
        } },
        .{ .Text = try conversation.textualBlockFromSlice(allocator, "answer") },
    }, null);
    try conversation.setThinkingOrigins(allocator, conv.messages.items[0].content.items, .openai_responses, "https://api.individual.githubcopilot.com", "gpt-5.4-mini");

    const cfg = testConfig("claude-x");
    var empty_tools = tool_registry_mod.ToolRegistry.init(allocator);
    defer empty_tools.deinit();
    const body = try serializeRequest(allocator, &cfg, &conv, &empty_tools);
    defer allocator.free(body);

    var parsed = try std.json.parseFromSlice(std.json.Value, allocator, body, .{});
    defer parsed.deinit();

    const content = parsed.value.object.get("messages").?.array.items[0]
        .object.get("content").?.array.items;
    try testing.expectEqual(@as(usize, 1), content.len);
    try testing.expectEqualStrings("text", content[0].object.get("type").?.string);
}

test "serializeRequest - unsigned Thinking blocks are dropped" {
    // Anthropic rejects thinking blocks without a valid signature on inbound
    // messages. If a block lacks one (e.g. from a different provider or an
    // interrupted stream), omit it rather than send a guaranteed-400 request.
    const allocator = testing.allocator;

    var conv = conversation.Conversation.init(allocator);
    defer conv.deinit();

    try conv.addAssistantMessage(&.{
        .{ .Thinking = .{
            .text = try conversation.textualBlockFromSlice(allocator, "unsigned thinking"),
            .signature = null,
        } },
        .{ .Text = try conversation.textualBlockFromSlice(allocator, "answer") },
    }, null);

    const cfg = testConfig("claude-x");
    var empty_tools = tool_registry_mod.ToolRegistry.init(allocator);
    defer empty_tools.deinit();
    const body = try serializeRequest(allocator, &cfg, &conv, &empty_tools);
    defer allocator.free(body);

    var parsed = try std.json.parseFromSlice(std.json.Value, allocator, body, .{});
    defer parsed.deinit();

    const content = parsed.value.object.get("messages").?.array.items[0]
        .object.get("content").?.array.items;
    try testing.expectEqual(@as(usize, 1), content.len);
    try testing.expectEqualStrings("text", content[0].object.get("type").?.string);
}

test "parseStreamEvent - message_start" {
    const allocator = testing.allocator;
    const payload =
        \\{"type":"message_start","message":{"id":"msg_1","type":"message","role":"assistant","content":[],"model":"claude","stop_reason":null}}
    ;
    var pe = try parseStreamEvent(allocator, payload);
    defer pe.deinit();
    try testing.expectEqual(StreamEventTag.message_start, @as(StreamEventTag, pe.event));
    try testing.expectEqualStrings("assistant", pe.event.message_start.role.?);
}

test "parseStreamEvent - content_block_start text" {
    const allocator = testing.allocator;
    const payload =
        \\{"type":"content_block_start","index":0,"content_block":{"type":"text","text":""}}
    ;
    var pe = try parseStreamEvent(allocator, payload);
    defer pe.deinit();
    try testing.expectEqual(StreamEventTag.content_block_start, @as(StreamEventTag, pe.event));
    try testing.expectEqual(@as(usize, 0), pe.event.content_block_start.index);
    try testing.expectEqual(ContentBlockKind.text, pe.event.content_block_start.kind);
}

test "parseStreamEvent - content_block_start thinking" {
    const allocator = testing.allocator;
    const payload =
        \\{"type":"content_block_start","index":0,"content_block":{"type":"thinking","thinking":"","signature":""}}
    ;
    var pe = try parseStreamEvent(allocator, payload);
    defer pe.deinit();
    try testing.expectEqual(ContentBlockKind.thinking, pe.event.content_block_start.kind);
}

test "parseStreamEvent - text_delta" {
    const allocator = testing.allocator;
    const payload =
        \\{"type":"content_block_delta","index":1,"delta":{"type":"text_delta","text":"Hello"}}
    ;
    var pe = try parseStreamEvent(allocator, payload);
    defer pe.deinit();
    try testing.expectEqual(@as(usize, 1), pe.event.content_block_delta.index);
    try testing.expectEqualStrings("Hello", pe.event.content_block_delta.text_delta.?);
    try testing.expect(pe.event.content_block_delta.thinking_delta == null);
}

test "parseStreamEvent - thinking_delta" {
    const allocator = testing.allocator;
    const payload =
        \\{"type":"content_block_delta","index":0,"delta":{"type":"thinking_delta","thinking":"step 1"}}
    ;
    var pe = try parseStreamEvent(allocator, payload);
    defer pe.deinit();
    try testing.expectEqualStrings("step 1", pe.event.content_block_delta.thinking_delta.?);
}

test "parseStreamEvent - signature_delta" {
    const allocator = testing.allocator;
    const payload =
        \\{"type":"content_block_delta","index":0,"delta":{"type":"signature_delta","signature":"abc123"}}
    ;
    var pe = try parseStreamEvent(allocator, payload);
    defer pe.deinit();
    try testing.expectEqualStrings("abc123", pe.event.content_block_delta.signature_delta.?);
}

test "parseStreamEvent - content_block_stop" {
    const allocator = testing.allocator;
    const payload =
        \\{"type":"content_block_stop","index":2}
    ;
    var pe = try parseStreamEvent(allocator, payload);
    defer pe.deinit();
    try testing.expectEqual(@as(usize, 2), pe.event.content_block_stop.index);
}

test "parseStreamEvent - message_delta stop_reason" {
    const allocator = testing.allocator;
    const payload =
        \\{"type":"message_delta","delta":{"stop_reason":"end_turn","stop_sequence":null}}
    ;
    var pe = try parseStreamEvent(allocator, payload);
    defer pe.deinit();
    try testing.expectEqualStrings("end_turn", pe.event.message_delta.stop_reason.?);
}

test "parseStreamEvent - message_stop" {
    const allocator = testing.allocator;
    const payload =
        \\{"type":"message_stop"}
    ;
    var pe = try parseStreamEvent(allocator, payload);
    defer pe.deinit();
    try testing.expectEqual(StreamEventTag.message_stop, @as(StreamEventTag, pe.event));
}

test "parseStreamEvent - ping" {
    const allocator = testing.allocator;
    const payload = "{\"type\":\"ping\"}";
    var pe = try parseStreamEvent(allocator, payload);
    defer pe.deinit();
    try testing.expectEqual(StreamEventTag.ping, @as(StreamEventTag, pe.event));
}

test "parseStreamEvent - error" {
    const allocator = testing.allocator;
    const payload =
        \\{"type":"error","error":{"type":"overloaded_error","message":"too busy"}}
    ;
    var pe = try parseStreamEvent(allocator, payload);
    defer pe.deinit();
    try testing.expectEqualStrings("overloaded_error", pe.event.@"error".kind.?);
    try testing.expectEqualStrings("too busy", pe.event.@"error".message.?);
}

test "parseStreamEvent - unknown type" {
    const allocator = testing.allocator;
    const payload =
        \\{"type":"some_future_event","extra":"data"}
    ;
    var pe = try parseStreamEvent(allocator, payload);
    defer pe.deinit();
    try testing.expectEqual(StreamEventTag.unknown, @as(StreamEventTag, pe.event));
}

// -----------------------------------------------------------------------------
// Phase 3: tools serialization, ToolUse + ToolResult content blocks
// -----------------------------------------------------------------------------

const tool_mod = @import("tool.zig");

const StaticToolVT = struct {
    fn invoke(_: *anyopaque, _: []const u8, _: Allocator) anyerror!tool_mod.ResultParts {
        return error.NotImplementedInTest;
    }
    fn deinit_(_: *anyopaque, _: Allocator) void {}
    const v: tool_mod.Tool.VTable = .{ .invoke = invoke, .deinit = deinit_ };
};
var static_tool_ctx_sentinel: u8 = 0;
fn makeStaticTool(
    name: []const u8,
    description: []const u8,
    schema: []const u8,
) tool_mod.Tool {
    return .{
        .decl = .{
            .name = name,
            .description = description,
            .schema_json = schema,
        },
        .ctx = &static_tool_ctx_sentinel,
        .vtable = &StaticToolVT.v,
    };
}

test "serializeRequest - emits tools array when registry non-empty" {
    const allocator = testing.allocator;

    var conv = conversation.Conversation.init(allocator);
    defer conv.deinit();
    try addUserText(&conv, "call something");

    var tools = tool_registry_mod.ToolRegistry.init(allocator);
    defer tools.deinit();
    try tools.register(makeStaticTool("echo", "Echo a message back.",
        \\{"type":"object","properties":{"message":{"type":"string"}},"required":["message"]}
    ));

    const cfg = testConfig("claude-x");
    const body = try serializeRequest(allocator, &cfg, &conv, &tools);
    defer allocator.free(body);

    var parsed = try std.json.parseFromSlice(std.json.Value, allocator, body, .{});
    defer parsed.deinit();

    const arr = parsed.value.object.get("tools").?.array.items;
    try testing.expectEqual(@as(usize, 1), arr.len);
    try testing.expectEqualStrings("echo", arr[0].object.get("name").?.string);
    try testing.expectEqualStrings("Echo a message back.", arr[0].object.get("description").?.string);

    const schema = arr[0].object.get("input_schema").?.object;
    try testing.expectEqualStrings("object", schema.get("type").?.string);
    try testing.expect(schema.get("properties").? == .object);
}

test "serializeRequest - dotted names are wire-encoded in tools and history" {
    const allocator = testing.allocator;

    var conv = conversation.Conversation.init(allocator);
    defer conv.deinit();
    // A prior assistant tool_use replayed from history (dotted internally).
    const id = try allocator.dupe(u8, "tu_1");
    const name = try allocator.dupe(u8, "std.write");
    var input: conversation.TextualBlock = .empty;
    try input.appendSlice(allocator, "{}");
    try conv.addAssistantMessage(&.{
        .{ .ToolUse = .{ .id = id, .name = name, .input = input } },
    }, null);

    var tools = tool_registry_mod.ToolRegistry.init(allocator);
    defer tools.deinit();
    try tools.register(makeStaticTool("std.read", "Read.", "{\"type\":\"object\"}"));

    const cfg = testConfig("claude-x");
    const body = try serializeRequest(allocator, &cfg, &conv, &tools);
    defer allocator.free(body);

    var parsed = try std.json.parseFromSlice(std.json.Value, allocator, body, .{});
    defer parsed.deinit();

    // Tool list: `std.read` -> `std__read`.
    const tool_name = parsed.value.object.get("tools").?.array.items[0]
        .object.get("name").?.string;
    try testing.expectEqualStrings("std__read", tool_name);

    // Replayed history tool_use: `std.write` -> `std__write`.
    const hist_name = parsed.value.object.get("messages").?.array.items[0]
        .object.get("content").?.array.items[0].object.get("name").?.string;
    try testing.expectEqualStrings("std__write", hist_name);
}

test "serializeRequest - assistant ToolUse becomes tool_use content block" {
    const allocator = testing.allocator;

    var conv = conversation.Conversation.init(allocator);
    defer conv.deinit();

    const id = try allocator.dupe(u8, "tu_1");
    const name = try allocator.dupe(u8, "echo");
    var input: conversation.TextualBlock = .empty;
    try input.appendSlice(allocator, "{\"message\":\"hi\"}");

    try conv.addAssistantMessage(&.{
        .{ .Text = try conversation.textualBlockFromSlice(allocator, "calling tool") },
        .{ .ToolUse = .{ .id = id, .name = name, .input = input } },
    }, null);

    var empty_tools = tool_registry_mod.ToolRegistry.init(allocator);
    defer empty_tools.deinit();
    const cfg = testConfig("claude-x");
    const body = try serializeRequest(allocator, &cfg, &conv, &empty_tools);
    defer allocator.free(body);

    var parsed = try std.json.parseFromSlice(std.json.Value, allocator, body, .{});
    defer parsed.deinit();

    const content = parsed.value.object.get("messages").?.array.items[0]
        .object.get("content").?.array.items;
    try testing.expectEqual(@as(usize, 2), content.len);
    try testing.expectEqualStrings("text", content[0].object.get("type").?.string);

    try testing.expectEqualStrings("tool_use", content[1].object.get("type").?.string);
    try testing.expectEqualStrings("tu_1", content[1].object.get("id").?.string);
    try testing.expectEqualStrings("echo", content[1].object.get("name").?.string);
    // `input` is a nested JSON object, NOT a string.
    const inp = content[1].object.get("input").?.object;
    try testing.expectEqualStrings("hi", inp.get("message").?.string);
}

test "serializeRequest - user ToolResult becomes tool_result content block" {
    const allocator = testing.allocator;

    var conv = conversation.Conversation.init(allocator);
    defer conv.deinit();

    const id = try allocator.dupe(u8, "tu_1");
    var parts: std.ArrayList(conversation.ResultPartStored) = .empty;
    try parts.append(allocator, .{ .text = try conversation.textualBlockFromSlice(allocator, "the answer is 42") });

    var blocks: std.ArrayList(conversation.ContentBlock) = .empty;
    try blocks.append(allocator, .{ .ToolResult = .{ .tool_use_id = id, .parts = parts } });
    try conv.messages.append(allocator, .{ .role = .user, .content = blocks });

    var empty_tools = tool_registry_mod.ToolRegistry.init(allocator);
    defer empty_tools.deinit();
    const cfg = testConfig("claude-x");
    const body = try serializeRequest(allocator, &cfg, &conv, &empty_tools);
    defer allocator.free(body);

    var parsed = try std.json.parseFromSlice(std.json.Value, allocator, body, .{});
    defer parsed.deinit();

    const msg = parsed.value.object.get("messages").?.array.items[0].object;
    try testing.expectEqualStrings("user", msg.get("role").?.string);

    const arr = msg.get("content").?.array.items;
    try testing.expectEqual(@as(usize, 1), arr.len);
    try testing.expectEqualStrings("tool_result", arr[0].object.get("type").?.string);
    try testing.expectEqualStrings("tu_1", arr[0].object.get("tool_use_id").?.string);
    // A successful result omits the is_error marker entirely.
    try testing.expect(arr[0].object.get("is_error") == null);
    const tr_content = arr[0].object.get("content").?.array.items;
    try testing.expectEqual(@as(usize, 1), tr_content.len);
    try testing.expectEqualStrings("text", tr_content[0].object.get("type").?.string);
    try testing.expectEqualStrings("the answer is 42", tr_content[0].object.get("text").?.string);
}

test "serializeRequest - error ToolResult emits is_error: true" {
    const allocator = testing.allocator;

    var conv = conversation.Conversation.init(allocator);
    defer conv.deinit();

    const id = try allocator.dupe(u8, "tu_err");
    var parts: std.ArrayList(conversation.ResultPartStored) = .empty;
    try parts.append(allocator, .{ .text = try conversation.textualBlockFromSlice(allocator, "file not found") });

    var blocks: std.ArrayList(conversation.ContentBlock) = .empty;
    try blocks.append(allocator, .{ .ToolResult = .{ .tool_use_id = id, .parts = parts, .is_error = true } });
    try conv.messages.append(allocator, .{ .role = .user, .content = blocks });

    var empty_tools = tool_registry_mod.ToolRegistry.init(allocator);
    defer empty_tools.deinit();
    const cfg = testConfig("claude-x");
    const body = try serializeRequest(allocator, &cfg, &conv, &empty_tools);
    defer allocator.free(body);

    var parsed = try std.json.parseFromSlice(std.json.Value, allocator, body, .{});
    defer parsed.deinit();

    const msg = parsed.value.object.get("messages").?.array.items[0].object;
    const arr = msg.get("content").?.array.items;
    try testing.expectEqualStrings("tool_result", arr[0].object.get("type").?.string);
    try testing.expect(arr[0].object.get("is_error").?.bool);
}

test "serializeRequest - tool result with image part emits image block" {
    const allocator = testing.allocator;

    var conv = conversation.Conversation.init(allocator);
    defer conv.deinit();

    const id = try allocator.dupe(u8, "tu_img");
    var parts: std.ArrayList(conversation.ResultPartStored) = .empty;
    try parts.append(allocator, .{ .text = try conversation.textualBlockFromSlice(allocator, "the file:") });
    try parts.append(allocator, .{ .media = .{
        .media_type = try allocator.dupe(u8, "image/png"),
        .data = try conversation.textualBlockFromSlice(allocator, "iVBOR=="),
    } });
    var blocks: std.ArrayList(conversation.ContentBlock) = .empty;
    try blocks.append(allocator, .{ .ToolResult = .{ .tool_use_id = id, .parts = parts } });
    try conv.messages.append(allocator, .{ .role = .user, .content = blocks });

    var empty_tools = tool_registry_mod.ToolRegistry.init(allocator);
    defer empty_tools.deinit();
    const cfg = testConfig("claude-x");
    const body = try serializeRequest(allocator, &cfg, &conv, &empty_tools);
    defer allocator.free(body);

    var parsed = try std.json.parseFromSlice(std.json.Value, allocator, body, .{});
    defer parsed.deinit();

    const msg = parsed.value.object.get("messages").?.array.items[0].object;
    const arr = msg.get("content").?.array.items[0].object.get("content").?.array.items;
    try testing.expectEqual(@as(usize, 2), arr.len);
    try testing.expectEqualStrings("text", arr[0].object.get("type").?.string);
    try testing.expectEqualStrings("image", arr[1].object.get("type").?.string);
    const src = arr[1].object.get("source").?.object;
    try testing.expectEqualStrings("base64", src.get("type").?.string);
    try testing.expectEqualStrings("image/png", src.get("media_type").?.string);
    try testing.expectEqualStrings("iVBOR==", src.get("data").?.string);
}

test "serializeRequest - thinking disabled omits thinking and effort fields" {
    const allocator = testing.allocator;
    var conv = conversation.Conversation.init(allocator);
    defer conv.deinit();
    try addUserText(&conv, "hi");

    var cfg = testConfig("claude-x");
    cfg.thinking = .disabled;
    var empty_tools = tool_registry_mod.ToolRegistry.init(allocator);
    defer empty_tools.deinit();
    const body = try serializeRequest(allocator, &cfg, &conv, &empty_tools);
    defer allocator.free(body);

    var parsed = try std.json.parseFromSlice(std.json.Value, allocator, body, .{});
    defer parsed.deinit();
    const root = parsed.value.object;
    try testing.expect(root.get("thinking") == null);
    try testing.expect(root.get("effort") == null);
}

test "serializeRequest - thinking enabled explicit budget" {
    const allocator = testing.allocator;
    var conv = conversation.Conversation.init(allocator);
    defer conv.deinit();
    try addUserText(&conv, "hi");

    var cfg = testConfig("claude-x"); // max_tokens = 1024
    cfg.thinking = .enabled;
    cfg.thinking_budget_tokens = 500; // within max_tokens
    var empty_tools = tool_registry_mod.ToolRegistry.init(allocator);
    defer empty_tools.deinit();
    const body = try serializeRequest(allocator, &cfg, &conv, &empty_tools);
    defer allocator.free(body);

    var parsed = try std.json.parseFromSlice(std.json.Value, allocator, body, .{});
    defer parsed.deinit();
    const root = parsed.value.object;
    const th = root.get("thinking").?.object;
    try testing.expectEqualStrings("enabled", th.get("type").?.string);
    try testing.expectEqual(@as(i64, 500), th.get("budget_tokens").?.integer);
    try testing.expectEqualStrings("summarized", th.get("display").?.string);
    try testing.expect(root.get("effort") == null);
}

test "serializeRequest - thinking enabled null budget falls back to max_tokens - 1" {
    const allocator = testing.allocator;
    var conv = conversation.Conversation.init(allocator);
    defer conv.deinit();
    try addUserText(&conv, "hi");

    var cfg = testConfig("claude-x"); // max_tokens = 1024
    cfg.thinking = .enabled;
    cfg.thinking_budget_tokens = null;
    var empty_tools = tool_registry_mod.ToolRegistry.init(allocator);
    defer empty_tools.deinit();
    const body = try serializeRequest(allocator, &cfg, &conv, &empty_tools);
    defer allocator.free(body);

    var parsed = try std.json.parseFromSlice(std.json.Value, allocator, body, .{});
    defer parsed.deinit();
    const th = parsed.value.object.get("thinking").?.object;
    try testing.expectEqual(@as(i64, 1023), th.get("budget_tokens").?.integer);
}

test "serializeRequest - thinking enabled budget clamped when >= max_tokens" {
    const allocator = testing.allocator;
    var conv = conversation.Conversation.init(allocator);
    defer conv.deinit();
    try addUserText(&conv, "hi");

    var cfg = testConfig("claude-x"); // max_tokens = 1024
    cfg.thinking = .enabled;
    cfg.thinking_budget_tokens = 2_000; // > max_tokens
    var empty_tools = tool_registry_mod.ToolRegistry.init(allocator);
    defer empty_tools.deinit();
    const body = try serializeRequest(allocator, &cfg, &conv, &empty_tools);
    defer allocator.free(body);

    var parsed = try std.json.parseFromSlice(std.json.Value, allocator, body, .{});
    defer parsed.deinit();
    const th = parsed.value.object.get("thinking").?.object;
    // Clamped to max_tokens - 1 = 1023
    try testing.expectEqual(@as(i64, 1023), th.get("budget_tokens").?.integer);
}

test "serializeRequest - thinking adaptive default effort" {
    const allocator = testing.allocator;
    var conv = conversation.Conversation.init(allocator);
    defer conv.deinit();
    try addUserText(&conv, "hi");

    var cfg = testConfig("claude-x");
    cfg.thinking = .adaptive;
    // effort defaults to .medium
    var empty_tools = tool_registry_mod.ToolRegistry.init(allocator);
    defer empty_tools.deinit();
    const body = try serializeRequest(allocator, &cfg, &conv, &empty_tools);
    defer allocator.free(body);

    var parsed = try std.json.parseFromSlice(std.json.Value, allocator, body, .{});
    defer parsed.deinit();
    const root = parsed.value.object;
    const th = root.get("thinking").?.object;
    try testing.expectEqualStrings("adaptive", th.get("type").?.string);
    try testing.expectEqualStrings("summarized", th.get("display").?.string);
    try testing.expect(th.get("budget_tokens") == null);
    try testing.expect(root.get("effort") == null);
    const oc = root.get("output_config").?.object;
    try testing.expectEqualStrings("medium", oc.get("effort").?.string);
}

test "serializeRequest - thinking adaptive explicit effort levels" {
    const allocator = testing.allocator;
    const efforts = [_]struct { e: config_mod.Effort, name: []const u8 }{
        .{ .e = .low, .name = "low" },
        .{ .e = .medium, .name = "medium" },
        .{ .e = .high, .name = "high" },
        .{ .e = .xhigh, .name = "xhigh" },
        .{ .e = .max, .name = "max" },
    };
    for (efforts) |entry| {
        var conv = conversation.Conversation.init(allocator);
        defer conv.deinit();
        try addUserText(&conv, "hi");

        var cfg = testConfig("claude-x");
        cfg.thinking = .adaptive;
        cfg.effort = entry.e;
        var empty_tools = tool_registry_mod.ToolRegistry.init(allocator);
        defer empty_tools.deinit();
        const body = try serializeRequest(allocator, &cfg, &conv, &empty_tools);
        defer allocator.free(body);

        var parsed = try std.json.parseFromSlice(std.json.Value, allocator, body, .{});
        defer parsed.deinit();
        const oc = parsed.value.object.get("output_config").?.object;
        try testing.expectEqualStrings(entry.name, oc.get("effort").?.string);
    }
}

test "serializeRequest - thinking adaptive ignores budget_tokens" {
    const allocator = testing.allocator;
    var conv = conversation.Conversation.init(allocator);
    defer conv.deinit();
    try addUserText(&conv, "hi");

    var cfg = testConfig("claude-x");
    cfg.thinking = .adaptive;
    cfg.thinking_budget_tokens = 9_999; // should be ignored
    var empty_tools = tool_registry_mod.ToolRegistry.init(allocator);
    defer empty_tools.deinit();
    const body = try serializeRequest(allocator, &cfg, &conv, &empty_tools);
    defer allocator.free(body);

    var parsed = try std.json.parseFromSlice(std.json.Value, allocator, body, .{});
    defer parsed.deinit();
    const th = parsed.value.object.get("thinking").?.object;
    try testing.expect(th.get("budget_tokens") == null);
}

test "serializeRequest - empty ToolUse input becomes {} not invalid JSON" {
    const allocator = testing.allocator;

    var conv = conversation.Conversation.init(allocator);
    defer conv.deinit();

    const id = try allocator.dupe(u8, "tu_1");
    const name = try allocator.dupe(u8, "noargs");
    try conv.addAssistantMessage(&.{
        .{ .ToolUse = .{ .id = id, .name = name, .input = .empty } },
    }, null);

    var empty_tools = tool_registry_mod.ToolRegistry.init(allocator);
    defer empty_tools.deinit();
    const cfg = testConfig("claude-x");
    const body = try serializeRequest(allocator, &cfg, &conv, &empty_tools);
    defer allocator.free(body);

    var parsed = try std.json.parseFromSlice(std.json.Value, allocator, body, .{});
    defer parsed.deinit();

    const tu = parsed.value.object.get("messages").?.array.items[0]
        .object.get("content").?.array.items[0].object;
    try testing.expectEqualStrings("tool_use", tu.get("type").?.string);
    try testing.expect(tu.get("input").? == .object);
    try testing.expectEqual(@as(usize, 0), tu.get("input").?.object.count());
}