//! Layered `config.toml` loader for the panto CLI.
//!
//! Four files are read and merged, lowest precedence first:
//!
//!   1. base     — `${XDG_DATA_HOME:-$HOME/.local/share}/panto/config.toml`
//!   2. user     — `${XDG_CONFIG_HOME:-$HOME/.config}/panto/config.toml`
//!   3. project  — `./.panto/config.toml`
//!   4. local    — `./.panto/config.local.toml`
//!
//! The `local` layer is intended to be git-ignored: it lets an individual
//! developer apply more-opinionated overrides on top of the team-shared
//! `project` layer without committing them.
//!
//! Merge semantics: **tables merge recursively; scalars and arrays from a
//! higher-precedence layer overwrite wholesale.** A project file that sets
//! `tools.deny = [...]` replaces the array entirely — it does not append to
//! a user-level `tools.deny`. Tables (notably `providers`) accumulate: a
//! provider defined only at the base layer survives even when the project
//! layer adds a different provider.
//!
//! After merge, the document is resolved into a `Config`:
//!
//!   - Every `auth.<name>` becomes a `ResolvedAuth` — a named auth session
//!     (`api_key` or `oauth_device`; `type` is inferred from the keys present
//!     when omitted). All values support `${...}` substitution: `${env:VAR}`
//!     reads the environment, `${sibling}` reads another key in the same
//!     section. For `api_key`, `key` is resolved eagerly (usually
//!     `"${env:VAR}"`); an empty result leaves the session **unresolved**, and
//!     any provider using it is dropped. OAuth sessions carry their flow config
//!     and are resolved at turn time.
//!   - Every `providers.<name>` becomes a `Provider`. A networked provider
//!     **must** name its auth session via `auth = "<name>"` (clean break:
//!     provider-level `api_key`/`api_key_env_var` are no longer accepted).
//!     A provider survives config resolution even when its auth is not
//!     currently resolved. 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. `model_catalog_name = <string>` optionally maps the
//!     provider to an external model catalog key (sync tooling otherwise
//!     falls back to the provider name). `extra_headers` (a table of string
//!     headers) rides on the model request.
//!   - `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
//!     for the same kind is a hard error.
//!
//! Model *aliases* (the `<model_alias>` half of a model reference) are
//! resolved separately against `models.toml` — this module only validates
//! that the reference names a known provider.

const std = @import("std");
const Allocator = std.mem.Allocator;
const Io = std.Io;

const toml = @import("toml");
const panto = @import("panto");

const glob = @import("glob.zig");
const models_toml = @import("models_toml.zig");

// Document-building helpers live in the toml library's `value` module and
// are not re-exported at its root. `tableIterator` *is* re-exported, so we
// use `toml.tableIterator` directly but reach through `value_mod` for the
// constructors/mutators.
const tvalue = toml.value_mod;

pub const APIStyle = panto.APIStyle;

// ===========================================================================
// Resolved config model
// ===========================================================================

/// One resolved provider. Transport-only: it names the auth session that
/// supplies its credential (`auth_name`); the credential itself is resolved
/// separately (eagerly for `api_key`, at turn time for OAuth). A provider
/// always survives config resolution, even when its auth is unresolved.
pub const Provider = struct {
    /// The user-chosen provider name (the `providers.<name>` key). This is
    /// the name used on the left of a `<provider>:<model>` reference.
    name: []const u8,
    style: APIStyle,
    /// User-facing sub-dialect for styles that share a protocol family.
    /// Currently only `style = "openai_responses"` supports `dialect = "codex"`,
    /// which maps to internal `APIStyle.openai_codex_responses`.
    dialect: ?[]const u8 = null,
    base_url: []const u8,
    /// The `auth.<name>` session this provider draws its credential from.
    auth_name: []const u8,
    /// Optional external model-catalog provider key (e.g. `github-copilot`
    /// on models.dev). Absent => sync tooling falls back to `name`.
    model_catalog_name: ?[]const u8 = null,
    /// 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,
    /// Static request headers merged onto the model request. Borrowed from
    /// the owning `Config`'s auth arena (freed with the Config, not here).
    extra_headers: []const panto.Header = &.{},

    pub fn deinit(self: Provider, alloc: Allocator) void {
        alloc.free(self.name);
        if (self.dialect) |d| alloc.free(d);
        alloc.free(self.base_url);
        alloc.free(self.auth_name);
        if (self.model_catalog_name) |m| alloc.free(m);
        // `extra_headers` lives in the Config auth arena; not freed here.
    }
};

/// Look up a resolved auth session by name in a slice. Returns null if absent.
fn authByName(auths: []const ResolvedAuth, name: []const u8) ?*const ResolvedAuth {
    for (auths) |*a| {
        if (std.mem.eql(u8, a.name, name)) return a;
    }
    return null;
}

/// One resolved named auth session (`auth.<name>`). The `config` carries the
/// auth-type-specific settings (borrowed from the Config auth arena).
/// `resolved_api_key` is set eagerly for `api_key` sessions whose key is
/// available now (literal or present env var); it is null for OAuth sessions
/// (resolved at turn time) and for `api_key` sessions whose env var is absent.
pub const ResolvedAuth = struct {
    name: []const u8,
    config: panto.AuthConfig,
    resolved_api_key: ?[]const u8 = null,
};

/// A parsed `<provider>:<model>` reference. Both halves borrow from the
/// owning `Config` (the `default_model` storage); do not free separately.
pub const ModelRef = struct {
    provider: []const u8,
    model: []const u8,
};

/// Tool/extension availability policy. Empty `allow` means "allow all"
/// (subject to `deny`). A name is permitted when it matches at least one
/// allow pattern (or allow is empty) AND matches no deny pattern.
pub const Policy = struct {
    allow: [][]const u8,
    deny: [][]const u8,

    pub fn deinit(self: Policy, alloc: Allocator) void {
        for (self.allow) |p| alloc.free(p);
        alloc.free(self.allow);
        for (self.deny) |p| alloc.free(p);
        alloc.free(self.deny);
    }

    /// True if `name` is permitted under this policy.
    pub fn permits(self: Policy, name: []const u8) bool {
        for (self.deny) |pat| {
            if (glob.match(pat, name)) return false;
        }
        if (self.allow.len == 0) return true;
        for (self.allow) |pat| {
            if (glob.match(pat, name)) return true;
        }
        return false;
    }
};

/// Build a `panto.ProviderConfig` for a chosen `<provider>:<alias>` model
/// reference, combining the resolved provider (transport/auth) with the
/// model definition from `models.toml` (wire name + knobs).
///
/// `ref` selects the provider and alias. `defs` supplies per-model knobs;
/// a missing alias falls back to using the alias verbatim as the wire
/// model name with default knobs. Returns the assembled `Config` plus the
/// wire model id (borrowed from `defs`/`ref` — valid as long as both
/// outlive the returned config's use). The `panto.ProviderConfig` itself
/// borrows the provider/model strings; the caller must keep `cfg` (the
/// `Config`) and `defs` alive for its lifetime.
pub fn buildProviderConfig(
    cfg: *const Config,
    defs: *const models_toml.ModelRegistry,
    ref: ModelRef,
) ResolveError!panto.ProviderConfig {
    const prov = cfg.provider(ref.provider) orelse return error.UnknownProvider;

    const auth_cfg = cfg.auth(prov.auth_name) orelse unreachable;

    // The provider's credential comes from its named auth session. For
    // `api_key` sessions this is resolved eagerly at load; for OAuth it is
    // null here and patched in at turn time by the embedder's auth manager
    // (which also supplies a dynamic base_url and auth-derived headers). An
    // empty string is a deliberate placeholder: an unresolved session yields
    // a clear auth error on its first request rather than a silent drop.
    const api_key: []const u8 = auth_cfg.resolved_api_key orelse "";
    const anthropic_use_bearer_auth = auth_cfg.config == .oauth_device;

    const def_opt = defs.get(ref.provider, ref.model);
    const wire_model: []const u8 = if (def_opt) |d| d.model else ref.model;
    const reasoning: panto.ReasoningEffort = if (def_opt) |d| d.reasoning else .default;
    const max_tokens: u32 = if (def_opt) |d| (d.max_tokens orelse 64_000) else 64_000;

    switch (prov.style) {
        .openai_chat => return .{ .openai_chat = .{
            .api_key = api_key,
            .base_url = prov.base_url,
            .model = wire_model,
            .reasoning = reasoning,
            .max_tokens = max_tokens,
            .extra_headers = prov.extra_headers,
        } },
        .anthropic_messages => return .{ .anthropic_messages = .{
            .api_key = api_key,
            .base_url = prov.base_url,
            .model = wire_model,
            .api_version = if (def_opt) |d| (d.api_version orelse "2023-06-01") else "2023-06-01",
            .max_tokens = max_tokens,
            .thinking = if (def_opt) |d| d.thinking else .disabled,
            .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,
            .use_bearer_auth = anthropic_use_bearer_auth,
            .extra_headers = prov.extra_headers,
        } },
        .openai_responses => return .{ .openai_responses = .{
            .api_key = api_key,
            .base_url = prov.base_url,
            .model = wire_model,
            .reasoning = reasoning,
            .max_tokens = max_tokens,
            .extra_headers = prov.extra_headers,
        } },
        .openai_codex_responses => return .{ .openai_codex_responses = .{
            .api_key = api_key,
            .base_url = prov.base_url,
            .model = wire_model,
            .reasoning = reasoning,
            .max_tokens = max_tokens,
            .extra_headers = prov.extra_headers,
        } },
    }
}

pub const Config = struct {
    allocator: Allocator,
    providers: []Provider,
    /// Named auth sessions (`auth.<name>`). All auth-config strings, header
    /// arrays, and provider `extra_headers` are owned by `auth_arena`.
    auths: []ResolvedAuth,
    /// Arena owning every auth-related allocation (auth names, `AuthConfig`
    /// string fields and header arrays, resolved api keys, and provider
    /// `extra_headers`). Freed wholesale in `deinit`.
    auth_arena: std.heap.ArenaAllocator,
    /// `defaults.model` storage, owned. `default_model_ref` slices into it.
    default_model: ?[]const u8,
    default_model_ref: ?ModelRef,
    tools: Policy,
    extensions: Policy,
    /// `[compaction]` settings. `compaction_keep_verbatim` is the kept-
    /// suffix token budget (null = use libpanto's default). `compaction_model`
    /// is an owned `<provider>:<alias>` reference string for the optional
    /// compaction-model override; `compaction_model_ref` slices into it.
    compaction_keep_verbatim: ?u32 = null,
    compaction_model: ?[]const u8 = null,
    compaction_model_ref: ?ModelRef = null,

    pub fn deinit(self: *Config) void {
        for (self.providers) |p| p.deinit(self.allocator);
        self.allocator.free(self.providers);
        self.allocator.free(self.auths);
        if (self.default_model) |m| self.allocator.free(m);
        if (self.compaction_model) |m| self.allocator.free(m);
        self.tools.deinit(self.allocator);
        self.extensions.deinit(self.allocator);
        // Frees every auth-config string, header array, resolved api key,
        // and provider `extra_headers` in one shot.
        self.auth_arena.deinit();
    }

    /// Look up a resolved provider by name. Returns null if absent.
    pub fn provider(self: *const Config, name: []const u8) ?*const Provider {
        for (self.providers) |*p| {
            if (std.mem.eql(u8, p.name, name)) return p;
        }
        return null;
    }

    /// Look up a named auth session. Returns null if absent.
    pub fn auth(self: *const Config, name: []const u8) ?*const ResolvedAuth {
        for (self.auths) |*a| {
            if (std.mem.eql(u8, a.name, name)) return a;
        }
        return null;
    }

    /// Choose the model reference to start with. Precedence:
    ///   1. an explicit `model_override` (e.g. a future `--model` flag),
    ///   2. `defaults.model` from config,
    ///   3. if exactly one provider resolved AND it has exactly one model
    ///      alias in `defs`, use that,
    ///   4. otherwise error (`NoModelSelected`).
    ///
    /// The returned ref borrows from `self`/`defs`/`model_override`.
    pub fn selectModel(
        self: *const Config,
        defs: *const models_toml.ModelRegistry,
        model_override: ?[]const u8,
    ) ResolveError!ModelRef {
        if (model_override) |m| {
            return parseModelRef(m) catch return error.NoModelSelected;
        }
        if (self.default_model_ref) |ref| return ref;

        // Single-provider, single-alias convenience.
        if (self.providers.len == 1) {
            const only = self.providers[0].name;
            var found: ?ModelRef = null;
            for (defs.entries.items) |d| {
                if (std.mem.eql(u8, d.provider, only)) {
                    if (found != null) {
                        found = null; // more than one alias; ambiguous.
                        break;
                    }
                    found = .{ .provider = d.provider, .model = d.alias };
                }
            }
            if (found) |ref| return ref;
        }
        return error.NoModelSelected;
    }
};

pub const Error = error{
    NoHomeDirectory,
    InvalidConfigToml,
    InvalidProvider,
    InvalidModelRef,
    UnknownDefaultProvider,
    PolicyConflict,
    /// An `[auth.<name>]` block is malformed (unknown/uninferable type, or a
    /// required field for its type is absent or substitutes to empty).
    InvalidAuth,
    /// A networked provider is missing `auth = "<name>"`.
    MissingProviderAuth,
    /// A provider's `auth = "<name>"` names a session with no `[auth.<name>]`.
    UnknownProviderAuth,
} || Allocator.Error || FileError;

pub const ResolveError = error{
    NoModelSelected,
    UnknownProvider,
};

/// The filesystem errors that can surface while reading a config layer.
/// `FileNotFound` is handled by the caller (skip the layer); any other
/// I/O failure is collapsed to `error.ConfigReadFailed` so this module
/// keeps a small, stable error set.
pub const FileError = Io.Cancelable || error{ FileNotFound, ConfigReadFailed };

// ===========================================================================
// Public entry points
// ===========================================================================

/// Resolve and merge the four config layers from their standard paths,
/// then build a `Config`. Missing files are skipped silently. `cwd` is the
/// project root (used for the `./.panto/config.toml` and
/// `./.panto/config.local.toml` layers).
pub fn load(
    allocator: Allocator,
    io: Io,
    environ_map: *const std.process.Environ.Map,
    cwd: []const u8,
) Error!Config {
    const paths = try layerPaths(allocator, environ_map, cwd);
    defer paths.deinit(allocator);

    return loadFromPaths(allocator, io, environ_map, &.{
        paths.base,
        paths.user,
        paths.project,
        paths.local,
    });
}

const LayerPaths = struct {
    base: []u8,
    user: []u8,
    project: []u8,
    local: []u8,

    fn deinit(self: LayerPaths, alloc: Allocator) void {
        alloc.free(self.base);
        alloc.free(self.user);
        alloc.free(self.project);
        alloc.free(self.local);
    }
};

fn layerPaths(
    allocator: Allocator,
    environ_map: *const std.process.Environ.Map,
    cwd: []const u8,
) Error!LayerPaths {
    const base = try baseConfigPath(allocator, environ_map);
    errdefer allocator.free(base);
    const user = try userConfigPath(allocator, environ_map);
    errdefer allocator.free(user);
    const project = try std.fs.path.join(allocator, &.{ cwd, ".panto", "config.toml" });
    errdefer allocator.free(project);
    const local = try std.fs.path.join(allocator, &.{ cwd, ".panto", "config.local.toml" });
    return .{ .base = base, .user = user, .project = project, .local = local };
}

/// `$PANTO_HOME/config.toml`, falling back to
/// `${XDG_DATA_HOME:-$HOME/.local/share}/panto/config.toml`.
///
/// `PANTO_HOME` is checked first so this always agrees with where the
/// bootstrap stages the default base config (see `panto_home.resolveHome`).
pub fn baseConfigPath(allocator: Allocator, environ_map: *const std.process.Environ.Map) Error![]u8 {
    if (environ_map.get("PANTO_HOME")) |home| {
        return try std.fs.path.join(allocator, &.{ home, "config.toml" });
    }
    if (environ_map.get("XDG_DATA_HOME")) |xdg| {
        return try std.fs.path.join(allocator, &.{ xdg, "panto", "config.toml" });
    }
    if (environ_map.get("HOME")) |home| {
        return try std.fs.path.join(allocator, &.{ home, ".local", "share", "panto", "config.toml" });
    }
    return error.NoHomeDirectory;
}

/// `${XDG_CONFIG_HOME:-$HOME/.config}/panto/config.toml`.
pub fn userConfigPath(allocator: Allocator, environ_map: *const std.process.Environ.Map) Error![]u8 {
    if (environ_map.get("XDG_CONFIG_HOME")) |xdg| {
        return try std.fs.path.join(allocator, &.{ xdg, "panto", "config.toml" });
    }
    if (environ_map.get("HOME")) |home| {
        return try std.fs.path.join(allocator, &.{ home, ".config", "panto", "config.toml" });
    }
    return error.NoHomeDirectory;
}

/// Resolve a `Config` from a single in-memory TOML string. Convenience for
/// tests and tooling that already hold the document text.
pub fn loadFromString(
    allocator: Allocator,
    environ_map: *const std.process.Environ.Map,
    source: []const u8,
) Error!Config {
    const doc = parseDoc(allocator, source) catch return error.InvalidConfigToml;
    defer doc.deinit();
    return resolve(allocator, environ_map, doc.root);
}

/// Load from explicit layer paths, lowest precedence first. Useful for
/// tests. Missing files are skipped.
pub fn loadFromPaths(
    allocator: Allocator,
    io: Io,
    environ_map: *const std.process.Environ.Map,
    paths: []const []const u8,
) Error!Config {
    // The merged document is built into its own arena-backed Document so we
    // never have to reason about which source layer a given Value came from.
    const merged = try tvalue.createDocument(allocator);
    defer merged.deinit();

    for (paths) |path| {
        const bytes = readFileAlloc(allocator, io, path) catch |err| switch (err) {
            error.FileNotFound => continue,
            else => return err,
        };
        defer allocator.free(bytes);

        const doc = parseDoc(allocator, bytes) catch return error.InvalidConfigToml;
        defer doc.deinit();
        try mergeTable(merged.allocator(), merged.root, doc.root);
    }

    return resolve(allocator, environ_map, merged.root);
}

// ===========================================================================
// Merge
// ===========================================================================

/// Deep-merge `src` table into `dst` table (both must be `.table`).
/// Tables recurse; everything else (scalars, arrays) overwrites. Values are
/// deep-copied into `alloc` (the merged document's arena) so they outlive
/// the source document.
fn mergeTable(alloc: Allocator, dst: *toml.Value, src: *const toml.Value) Allocator.Error!void {
    std.debug.assert(dst.* == .table);
    if (src.* != .table) return;

    var it = toml.tableIterator(src);
    while (it.next()) |entry| {
        const existing = dst.get(entry.key);
        if (existing != null and existing.?.* == .table and entry.value.* == .table) {
            // Both sides are tables — recurse to accumulate keys.
            try mergeTable(alloc, @constCast(existing.?), entry.value);
        } else {
            // Overwrite (or insert) with a deep copy of the source value.
            const copy = try cloneValue(alloc, entry.value);
            const key_copy = try alloc.dupe(u8, entry.key);
            try tvalue.tableSet(alloc, dst, key_copy, copy);
        }
    }
}

fn cloneValue(alloc: Allocator, src: *const toml.Value) Allocator.Error!*toml.Value {
    const out = try alloc.create(toml.Value);
    switch (src.*) {
        .table => {
            out.* = .{ .table = .{} };
            var it = toml.tableIterator(src);
            while (it.next()) |entry| {
                const child = try cloneValue(alloc, entry.value);
                const key_copy = try alloc.dupe(u8, entry.key);
                try tvalue.tableSet(alloc, out, key_copy, child);
            }
        },
        .array => |*a| {
            out.* = .{ .array = .{} };
            for (a.items.items) |*item| {
                const child = try cloneValue(alloc, item);
                try tvalue.arrayAppend(alloc, out, child.*);
            }
        },
        .string => |s| out.* = .{ .string = try alloc.dupe(u8, s) },
        else => out.* = src.*,
    }
    return out;
}

// ===========================================================================
// Resolve
// ===========================================================================

fn resolve(
    allocator: Allocator,
    environ_map: *const std.process.Environ.Map,
    root: *const toml.Value,
) Error!Config {
    // Arena owning every auth-related allocation. Moved into the returned
    // Config on success; deinit'd on any error path before then.
    var auth_arena = std.heap.ArenaAllocator.init(allocator);
    errdefer auth_arena.deinit();
    const aa = auth_arena.allocator();

    // Named auth sessions (`auth.<name>`), parsed first so providers can be
    // validated against them.
    var auths: std.ArrayList(ResolvedAuth) = .empty;
    errdefer auths.deinit(allocator);
    if (root.get("auth")) |auth_tbl| {
        if (auth_tbl.* == .table) {
            var it = toml.tableIterator(auth_tbl);
            while (it.next()) |entry| {
                const ra = try resolveAuth(aa, environ_map, entry.key, entry.value);
                try auths.append(allocator, ra);
            }
        }
    }

    var providers: std.ArrayList(Provider) = .empty;
    errdefer {
        for (providers.items) |p| p.deinit(allocator);
        providers.deinit(allocator);
    }

    if (root.get("providers")) |providers_tbl| {
        if (providers_tbl.* == .table) {
            var it = toml.tableIterator(providers_tbl);
            while (it.next()) |entry| {
                const p = try resolveProvider(allocator, aa, entry.key, entry.value);
                try providers.append(allocator, p);
            }
        }
    }

    // Every provider must name an auth session that exists.
    for (providers.items) |p| {
        if (authByName(auths.items, p.auth_name) == null) return error.UnknownProviderAuth;
    }

    // Drop any provider whose `api_key` session did not resolve (an absent
    // `${env:VAR}` reads as empty) — reproducing the "export your key or the
    // provider disappears" behavior for the default OpenAI/Anthropic entries.
    // OAuth providers always survive (resolved at turn time / via login). This
    // is an in-place, allocation-free compaction so a mid-loop failure can't
    // leave two slices owning the same strings.
    {
        var w: usize = 0;
        for (providers.items) |p| {
            const a = authByName(auths.items, p.auth_name).?;
            if (a.config == .api_key and a.resolved_api_key == null) {
                p.deinit(allocator);
            } else {
                providers.items[w] = p;
                w += 1;
            }
        }
        providers.shrinkRetainingCapacity(w);
    }

    // Tool / extension policies.
    var tools = try resolvePolicy(allocator, root, "tools");
    errdefer tools.deinit(allocator);
    var extensions = try resolvePolicy(allocator, root, "extensions");
    errdefer extensions.deinit(allocator);

    // Default model.
    var default_model: ?[]const u8 = null;
    errdefer if (default_model) |m| allocator.free(m);
    var default_model_ref: ?ModelRef = null;
    if (root.get("defaults")) |defaults_tbl| {
        if (defaults_tbl.get("model")) |model_v| {
            if (model_v.* == .string) {
                default_model = try allocator.dupe(u8, model_v.string);
                default_model_ref = try parseModelRef(default_model.?);
            }
        }
    }

    // `[compaction]` settings.
    var compaction_keep_verbatim: ?u32 = null;
    var compaction_model: ?[]const u8 = null;
    errdefer if (compaction_model) |m| allocator.free(m);
    var compaction_model_ref: ?ModelRef = null;
    if (root.get("compaction")) |compaction_tbl| {
        if (compaction_tbl.get("keep_verbatim")) |kv| {
            if (kv.* == .integer and kv.integer > 0) {
                compaction_keep_verbatim = @intCast(kv.integer);
            }
        }
        if (compaction_tbl.get("model")) |model_v| {
            if (model_v.* == .string) {
                compaction_model = try allocator.dupe(u8, model_v.string);
                compaction_model_ref = try parseModelRef(compaction_model.?);
            }
        }
    }

    const providers_slice = try providers.toOwnedSlice(allocator);
    errdefer {
        for (providers_slice) |p| p.deinit(allocator);
        allocator.free(providers_slice);
    }
    const auths_slice = try auths.toOwnedSlice(allocator);
    errdefer allocator.free(auths_slice);

    // Validate the default model names a provider that actually resolved.
    if (default_model_ref) |ref| {
        var found = false;
        for (providers_slice) |p| {
            if (std.mem.eql(u8, p.name, ref.provider)) {
                found = true;
                break;
            }
        }
        if (!found) return error.UnknownDefaultProvider;
    }

    // Validate the compaction-model override names a provider that resolved.
    if (compaction_model_ref) |ref| {
        var found = false;
        for (providers_slice) |p| {
            if (std.mem.eql(u8, p.name, ref.provider)) {
                found = true;
                break;
            }
        }
        if (!found) return error.UnknownDefaultProvider;
    }

    return .{
        .allocator = allocator,
        .providers = providers_slice,
        .auths = auths_slice,
        .auth_arena = auth_arena,
        .default_model = default_model,
        .default_model_ref = default_model_ref,
        .tools = tools,
        .extensions = extensions,
        .compaction_keep_verbatim = compaction_keep_verbatim,
        .compaction_model = compaction_model,
        .compaction_model_ref = compaction_model_ref,
    };
}

/// Resolve one `providers.<name>` entry. A provider always survives (no
/// silent drop): it names the auth session that supplies its credential, and
/// an unresolved session simply fails on first request. `name`/`base_url`/
/// `auth_name` are duped with `allocator`; `extra_headers` is allocated into
/// `aa` (the Config auth arena).
fn resolveProvider(
    allocator: Allocator,
    aa: Allocator,
    name: []const u8,
    val: *const toml.Value,
) Error!Provider {
    if (val.* != .table) return error.InvalidProvider;

    const style_str = (val.get("style") orelse return error.InvalidProvider).asString() orelse
        return error.InvalidProvider;
    var style = std.meta.stringToEnum(APIStyle, style_str) orelse return error.InvalidProvider;
    if (style == .openai_codex_responses) return error.InvalidProvider;
    const dialect = if (tomlStr(val, "dialect")) |d| d else null;
    if (dialect) |d| {
        if (std.mem.eql(u8, style_str, "openai_responses") and std.mem.eql(u8, d, "codex")) {
            style = .openai_codex_responses;
        } else {
            return error.InvalidProvider;
        }
    }

    const base_url = (val.get("base_url") orelse return error.InvalidProvider).asString() orelse
        return error.InvalidProvider;

    // Clean break: a networked provider must name its auth session.
    const auth_name = (val.get("auth") orelse return error.MissingProviderAuth).asString() orelse
        return error.MissingProviderAuth;

    const model_catalog_name = tomlStr(val, "model_catalog_name");

    // 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;
    };

    const extra_headers = try parseHeaders(aa, val.get("extra_headers"));

    return .{
        .name = try allocator.dupe(u8, name),
        .style = style,
        .dialect = if (dialect) |d| try allocator.dupe(u8, d) else null,
        .base_url = try allocator.dupe(u8, base_url),
        .auth_name = try allocator.dupe(u8, auth_name),
        .model_catalog_name = if (model_catalog_name) |m| try allocator.dupe(u8, m) else null,
        .prompt_cache = prompt_cache,
        .extra_headers = extra_headers,
    };
}

// ===========================================================================
// Auth resolution
// ===========================================================================

/// Parse one `auth.<name>` block into a `ResolvedAuth`. All strings are duped
/// into `aa` (the Config auth arena) after `${...}` substitution.
///
/// `type` is inferred when omitted: a `client_id` means `oauth_device`, a
/// `key` means `api_key`. For `api_key`, the credential is resolved eagerly
/// from `key` (which is usually `"${env:VAR}"`); an empty result leaves the
/// session unresolved (providers using it are later dropped).
fn resolveAuth(
    aa: Allocator,
    environ_map: *const std.process.Environ.Map,
    name: []const u8,
    val: *const toml.Value,
) Error!ResolvedAuth {
    if (val.* != .table) return error.InvalidAuth;

    const auth_type: panto.AuthType = blk: {
        if (tomlStr(val, "type")) |ts| {
            break :blk std.meta.stringToEnum(panto.AuthType, ts) orelse return error.InvalidAuth;
        }
        if (val.get("client_id") != null) break :blk .oauth_device;
        if (val.get("key") != null) break :blk .api_key;
        return error.InvalidAuth;
    };

    switch (auth_type) {
        .api_key => {
            // `key` after substitution; empty/absent => unresolved.
            const key = try substField(aa, environ_map, val, "key");
            return .{
                .name = try aa.dupe(u8, name),
                .config = .{ .api_key = .{ .key = key } },
                .resolved_api_key = key,
            };
        },
        .oauth_device => {
            const dialect = blk: {
                const ds = tomlStr(val, "dialect") orelse break :blk panto.DeviceDialect.token;
                break :blk std.meta.stringToEnum(panto.DeviceDialect, ds) orelse return error.InvalidAuth;
            };
            const fmt = blk: {
                const fs = tomlStr(val, "token_request_format") orelse break :blk panto.TokenRequestFormat.form;
                break :blk std.meta.stringToEnum(panto.TokenRequestFormat, fs) orelse return error.InvalidAuth;
            };
            const oauth: panto.OAuthDeviceAuth = .{
                .dialect = dialect,
                .client_id = (try substField(aa, environ_map, val, "client_id")) orelse return error.InvalidAuth,
                .device_code_url = (try substField(aa, environ_map, val, "device_code_url")) orelse return error.InvalidAuth,
                .token_url = (try substField(aa, environ_map, val, "token_url")) orelse return error.InvalidAuth,
                .device_poll_url = try substField(aa, environ_map, val, "device_poll_url"),
                .verification_url = try substField(aa, environ_map, val, "verification_url"),
                .scope = try substField(aa, environ_map, val, "scope"),
                .token_request_format = fmt,
                .redirect_uri = try substField(aa, environ_map, val, "redirect_uri"),
                .account_id_jwt_claim = try substField(aa, environ_map, val, "account_id_jwt_claim"),
                .exchange = try parseExchangeFlat(aa, environ_map, val),
            };
            // codex dialect needs a distinct poll endpoint.
            if (dialect == .codex and oauth.device_poll_url == null) return error.InvalidAuth;
            return .{
                .name = try aa.dupe(u8, name),
                .config = .{ .oauth_device = oauth },
                .resolved_api_key = null,
            };
        },
    }
}

/// Build the optional secondary exchange from flat `exchange_*` keys. Returns
/// null when `exchange_url` is absent.
fn parseExchangeFlat(
    aa: Allocator,
    environ_map: *const std.process.Environ.Map,
    val: *const toml.Value,
) Error!?panto.ExchangeConfig {
    const url = (try substField(aa, environ_map, val, "exchange_url")) orelse return null;
    return .{
        .url = url,
        .method = (try substField(aa, environ_map, val, "exchange_method")) orelse "GET",
        .token_json_path = (try substField(aa, environ_map, val, "exchange_token_path")) orelse "token",
        .expires_at_json_path = try substField(aa, environ_map, val, "exchange_expires_path"),
        .base_url_json_path = try substField(aa, environ_map, val, "exchange_base_url_path"),
    };
}

/// Read a string field from an auth table, run `${...}` substitution, and dupe
/// the result into `aa`. Returns null when the key is absent or substitutes to
/// the empty string (so an unset `${env:VAR}` reads as "unresolved").
fn substField(
    aa: Allocator,
    environ_map: *const std.process.Environ.Map,
    table: *const toml.Value,
    key: []const u8,
) Error!?[]const u8 {
    const raw = tomlStr(table, key) orelse return null;
    const v = try substitute(aa, environ_map, table, raw);
    return if (v.len == 0) null else v;
}

/// Substitute `${name}` placeholders in `raw`. `${env:VAR}` reads the
/// environment; any other `${name}` reads the raw value of sibling key `name`
/// in the same auth `table`. An unresolved reference (missing env var or
/// sibling key) substitutes to the empty string. Result is owned by `aa`.
fn substitute(
    aa: Allocator,
    environ_map: *const std.process.Environ.Map,
    table: *const toml.Value,
    raw: []const u8,
) Error![]const u8 {
    if (std.mem.indexOf(u8, raw, "${") == null) return aa.dupe(u8, raw);
    var out: std.ArrayList(u8) = .empty;
    errdefer out.deinit(aa);
    var i: usize = 0;
    while (i < raw.len) {
        if (raw[i] == '$' and i + 1 < raw.len and raw[i + 1] == '{') {
            const close = std.mem.indexOfScalarPos(u8, raw, i + 2, '}') orelse {
                // Unterminated `${` — emit the remainder literally.
                try out.appendSlice(aa, raw[i..]);
                break;
            };
            const ref = raw[i + 2 .. close];
            const value: []const u8 = if (std.mem.startsWith(u8, ref, "env:"))
                (environ_map.get(ref[4..]) orelse "")
            else
                (tomlStr(table, ref) orelse "");
            try out.appendSlice(aa, value);
            i = close + 1;
        } else {
            try out.append(aa, raw[i]);
            i += 1;
        }
    }
    return out.toOwnedSlice(aa);
}

/// Parse a `[...headers]` table of string keys/values into `[]panto.Header`,
/// allocated in `aa`. A null/absent table yields an empty slice.
fn parseHeaders(aa: Allocator, val: ?*const toml.Value) Error![]panto.Header {
    const v = val orelse return &.{};
    if (v.* != .table) return &.{};
    var list: std.ArrayList(panto.Header) = .empty;
    var it = toml.tableIterator(v);
    while (it.next()) |entry| {
        const value = entry.value.asString() orelse continue;
        try list.append(aa, .{
            .name = try aa.dupe(u8, entry.key),
            .value = try aa.dupe(u8, value),
        });
    }
    return list.toOwnedSlice(aa);
}

/// Borrow a string field from a table, or null if absent/non-string.
fn tomlStr(val: *const toml.Value, key: []const u8) ?[]const u8 {
    const v = val.get(key) orelse return null;
    return v.asString();
}

fn resolvePolicy(allocator: Allocator, root: *const toml.Value, key: []const u8) Error!Policy {
    var allow: [][]const u8 = &.{};
    var deny: [][]const u8 = &.{};
    errdefer {
        for (allow) |p| allocator.free(p);
        allocator.free(allow);
        for (deny) |p| allocator.free(p);
        allocator.free(deny);
    }

    if (root.get(key)) |tbl| {
        if (tbl.* == .table) {
            allow = try stringArray(allocator, tbl, "allow");
            deny = try stringArray(allocator, tbl, "deny");
        }
    }

    // A pattern present in both allow and deny is contradictory.
    for (allow) |a| {
        for (deny) |d| {
            if (std.mem.eql(u8, a, d)) return error.PolicyConflict;
        }
    }

    return .{ .allow = allow, .deny = deny };
}

fn stringArray(allocator: Allocator, tbl: *const toml.Value, key: []const u8) Error![][]const u8 {
    const arr_v = tbl.get(key) orelse return &.{};
    if (arr_v.* != .array) return &.{};

    var list: std.ArrayList([]const u8) = .empty;
    errdefer {
        for (list.items) |s| allocator.free(s);
        list.deinit(allocator);
    }
    for (arr_v.array.items.items) |*item| {
        if (item.* == .string) {
            try list.append(allocator, try allocator.dupe(u8, item.string));
        }
    }
    return try list.toOwnedSlice(allocator);
}

/// Parse `<provider>:<model>`. Both halves must be non-empty and there must
/// be exactly one separating colon.
pub fn parseModelRef(ref: []const u8) Error!ModelRef {
    const colon = std.mem.indexOfScalar(u8, ref, ':') orelse return error.InvalidModelRef;
    const provider = ref[0..colon];
    const model = ref[colon + 1 ..];
    if (provider.len == 0 or model.len == 0) return error.InvalidModelRef;
    if (std.mem.indexOfScalar(u8, model, ':') != null) return error.InvalidModelRef;
    return .{ .provider = provider, .model = model };
}

// ===========================================================================
// File / parse helpers
// ===========================================================================

fn readFileAlloc(allocator: Allocator, io: Io, path: []const u8) (Allocator.Error || FileError)![]u8 {
    const file = Io.Dir.cwd().openFile(io, path, .{ .mode = .read_only }) catch |err| switch (err) {
        error.FileNotFound => return error.FileNotFound,
        error.Canceled => return error.Canceled,
        else => return error.ConfigReadFailed,
    };
    defer file.close(io);
    const len = file.length(io) catch return error.ConfigReadFailed;
    const bytes = try allocator.alloc(u8, @intCast(len));
    errdefer allocator.free(bytes);
    _ = file.readPositionalAll(io, bytes, 0) catch |err| switch (err) {
        error.Canceled => return error.Canceled,
        else => return error.ConfigReadFailed,
    };
    return bytes;
}

fn parseDoc(allocator: Allocator, source: []const u8) !*toml.Document {
    const result = toml.parseWithError(allocator, source, .{});
    switch (result) {
        .err => |e| {
            if (!@import("builtin").is_test) {
                std.log.err(
                    "config.toml: parse error at line {d}, column {d}: {s}",
                    .{ e.line, e.column, e.message },
                );
            }
            return error.InvalidConfigToml;
        },
        .ok => |doc| return doc,
    }
}

// ===========================================================================
// Tests
// ===========================================================================

const testing = std.testing;

fn emptyEnv(a: Allocator) std.process.Environ.Map {
    return std.process.Environ.Map.init(a);
}

test "parseModelRef: splits provider and model" {
    const ref = try parseModelRef("anthropic:claude-sonnet-4-6");
    try testing.expectEqualStrings("anthropic", ref.provider);
    try testing.expectEqualStrings("claude-sonnet-4-6", ref.model);
}

test "parseModelRef: rejects malformed refs" {
    try testing.expectError(error.InvalidModelRef, parseModelRef("no-colon"));
    try testing.expectError(error.InvalidModelRef, parseModelRef(":model"));
    try testing.expectError(error.InvalidModelRef, parseModelRef("provider:"));
    try testing.expectError(error.InvalidModelRef, parseModelRef("a:b:c"));
}

test "Policy.permits: empty allow means allow-all minus deny" {
    const a = testing.allocator;
    var deny = try a.alloc([]const u8, 1);
    deny[0] = try a.dupe(u8, "std.shell");
    const policy: Policy = .{ .allow = &.{}, .deny = deny };
    defer policy.deinit(a);

    try testing.expect(policy.permits("std.read"));
    try testing.expect(!policy.permits("std.shell"));
}

test "Policy.permits: allow gates everything not matched" {
    const a = testing.allocator;
    var allow = try a.alloc([]const u8, 1);
    allow[0] = try a.dupe(u8, "std.*");
    const policy: Policy = .{ .allow = allow, .deny = &.{} };
    defer policy.deinit(a);

    try testing.expect(policy.permits("std.read"));
    try testing.expect(!policy.permits("other.read"));
}

/// Standard api_key provider+auth source for an anthropic provider whose key
/// comes from `ANTHROPIC_API_KEY`. Keeps the many model-knob tests terse.
const anthropic_env_src =
    \\[providers.anthropic]
    \\style = "anthropic_messages"
    \\base_url = "https://api.anthropic.com"
    \\auth = "anthropic_api"
    \\
    \\[auth.anthropic_api]
    \\key = "${env:ANTHROPIC_API_KEY}"
;

test "resolve: api_key provider is dropped when its ${env} key is unset" {
    const a = testing.allocator;
    var env = emptyEnv(a);
    defer env.deinit();

    const doc = try parseDoc(a, anthropic_env_src);
    defer doc.deinit();

    var cfg = try resolve(a, &env, doc.root);
    defer cfg.deinit();
    // Unresolved api_key ⇒ the provider disappears (export the key to get it
    // back). The auth session itself still exists.
    try testing.expectEqual(@as(usize, 0), cfg.providers.len);
    try testing.expect(cfg.provider("anthropic") == null);
    const auth = cfg.auth("anthropic_api").?;
    try testing.expect(auth.resolved_api_key == null);
    // `type` was inferred from the presence of `key`.
    try testing.expectEqual(panto.AuthType.api_key, @as(panto.AuthType, auth.config));
}

test "resolve: api_key session resolves when env var is set" {
    const a = testing.allocator;
    var env = emptyEnv(a);
    defer env.deinit();
    try env.put("ANTHROPIC_API_KEY", "sk-ant-xyz");

    const doc = try parseDoc(a, anthropic_env_src);
    defer doc.deinit();

    var cfg = try resolve(a, &env, doc.root);
    defer cfg.deinit();
    try testing.expectEqual(@as(usize, 1), cfg.providers.len);
    const p = cfg.provider("anthropic").?;
    try testing.expectEqual(APIStyle.anthropic_messages, p.style);
    try testing.expectEqualStrings("anthropic_api", p.auth_name);
    try testing.expectEqualStrings("sk-ant-xyz", cfg.auth("anthropic_api").?.resolved_api_key.?);
}

test "resolve: missing provider auth is an error" {
    const a = testing.allocator;
    var env = emptyEnv(a);
    defer env.deinit();
    const src =
        \\[providers.anthropic]
        \\style = "anthropic_messages"
        \\base_url = "https://api.anthropic.com"
    ;
    const doc = try parseDoc(a, src);
    defer doc.deinit();
    try testing.expectError(error.MissingProviderAuth, resolve(a, &env, doc.root));
}

test "resolve: provider naming an unknown auth session is an error" {
    const a = testing.allocator;
    var env = emptyEnv(a);
    defer env.deinit();
    const src =
        \\[providers.anthropic]
        \\style = "anthropic_messages"
        \\base_url = "https://api.anthropic.com"
        \\auth = "ghost"
    ;
    const doc = try parseDoc(a, src);
    defer doc.deinit();
    try testing.expectError(error.UnknownProviderAuth, resolve(a, &env, doc.root));
}

test "resolve: ${env:VAR} and ${sibling} substitution in auth values" {
    const a = testing.allocator;
    var env = emptyEnv(a);
    defer env.deinit();
    try env.put("MY_KEY", "sk-from-env");

    const src =
        \\[providers.openai]
        \\style = "openai_chat"
        \\base_url = "https://api.openai.com/v1"
        \\auth = "k"
        \\
        \\[auth.k]
        \\key = "${env:MY_KEY}"
        \\
        \\[providers.gh]
        \\style = "openai_chat"
        \\base_url = "https://example.com"
        \\auth = "gh"
        \\
        \\[auth.gh]
        \\client_id = "abc"
        \\domain = "github.com"
        \\device_code_url = "https://${domain}/login/device/code"
        \\token_url = "https://${domain}/login/oauth/access_token"
    ;
    const doc = try parseDoc(a, src);
    defer doc.deinit();

    var cfg = try resolve(a, &env, doc.root);
    defer cfg.deinit();
    // env substitution resolves the literal key.
    try testing.expectEqualStrings("sk-from-env", cfg.auth("k").?.resolved_api_key.?);
    // sibling-key substitution templates the device URLs (type inferred from
    // client_id).
    const oauth = cfg.auth("gh").?.config.oauth_device;
    try testing.expectEqualStrings("https://github.com/login/device/code", oauth.device_code_url);
    try testing.expectEqualStrings("https://github.com/login/oauth/access_token", oauth.token_url);
}

test "resolve: literal key resolves without substitution" {
    const a = testing.allocator;
    var env = emptyEnv(a);
    defer env.deinit();
    const src =
        \\[auth.k]
        \\key = "sk-literal"
    ;
    const doc = try parseDoc(a, src);
    defer doc.deinit();
    var cfg = try resolve(a, &env, doc.root);
    defer cfg.deinit();
    try testing.expectEqualStrings("sk-literal", cfg.auth("k").?.resolved_api_key.?);
}

test "resolve: invalid auth type is an error" {
    const a = testing.allocator;
    var env = emptyEnv(a);
    defer env.deinit();
    const src =
        \\[auth.bad]
        \\type = "magic"
    ;
    const doc = try parseDoc(a, src);
    defer doc.deinit();
    try testing.expectError(error.InvalidAuth, resolve(a, &env, doc.root));
}

test "resolve: oauth_device (token dialect) with exchange parses" {
    const a = testing.allocator;
    var env = emptyEnv(a);
    defer env.deinit();
    const src =
        \\[auth.github_copilot]
        \\client_id = "Iv1.b507a08c87ecfe98"
        \\domain = "github.com"
        \\device_code_url = "https://${domain}/login/device/code"
        \\token_url = "https://${domain}/login/oauth/access_token"
        \\scope = "read:user"
        \\exchange_url = "https://api.${domain}/copilot_internal/v2/token"
        \\exchange_expires_path = "expires_at"
        \\exchange_base_url_path = "endpoints.api"
    ;
    const doc = try parseDoc(a, src);
    defer doc.deinit();
    var cfg = try resolve(a, &env, doc.root);
    defer cfg.deinit();
    const oauth = cfg.auth("github_copilot").?.config.oauth_device;
    // type + dialect inferred/defaulted.
    try testing.expectEqual(panto.DeviceDialect.token, oauth.dialect);
    try testing.expectEqualStrings("Iv1.b507a08c87ecfe98", oauth.client_id);
    try testing.expectEqualStrings("https://github.com/login/device/code", oauth.device_code_url);
    try testing.expect(oauth.exchange != null);
    try testing.expectEqualStrings("https://api.github.com/copilot_internal/v2/token", oauth.exchange.?.url);
    try testing.expectEqualStrings("token", oauth.exchange.?.token_json_path); // default
    try testing.expectEqualStrings("endpoints.api", oauth.exchange.?.base_url_json_path.?);
}

test "resolve: oauth_device codex dialect requires a poll url" {
    const a = testing.allocator;
    var env = emptyEnv(a);
    defer env.deinit();
    const src =
        \\[auth.codex]
        \\type = "oauth_device"
        \\dialect = "codex"
        \\client_id = "app_x"
        \\device_code_url = "https://auth.openai.com/api/accounts/deviceauth/usercode"
        \\token_url = "https://auth.openai.com/oauth/token"
    ;
    const doc = try parseDoc(a, src);
    defer doc.deinit();
    try testing.expectError(error.InvalidAuth, resolve(a, &env, doc.root));
}

test "resolve: provider extra_headers flow into the built provider config" {
    const a = testing.allocator;
    var env = emptyEnv(a);
    defer env.deinit();
    const src =
        \\[providers.copilot]
        \\style = "openai_chat"
        \\base_url = "https://api.individual.githubcopilot.com"
        \\auth = "k"
        \\
        \\[providers.copilot.extra_headers]
        \\Copilot-Integration-Id = "vscode-chat"
        \\X-Initiator = "user"
        \\
        \\[auth.k]
        \\type = "api_key"
        \\key = "tok"
    ;
    const doc = try parseDoc(a, src);
    defer doc.deinit();
    var cfg = try resolve(a, &env, doc.root);
    defer cfg.deinit();

    const p = cfg.provider("copilot").?;
    try testing.expectEqual(@as(usize, 2), p.extra_headers.len);

    var models = models_toml.ModelRegistry.init(a);
    defer models.deinit();
    const pc = try buildProviderConfig(&cfg, &models, .{ .provider = "copilot", .model = "gpt-4o" });
    try testing.expectEqual(@as(usize, 2), pc.openai_chat.extra_headers.len);
    try testing.expectEqualStrings("tok", pc.openai_chat.api_key);
}

test "resolve: provider model_catalog_name is captured" {
    const a = testing.allocator;
    var env = emptyEnv(a);
    defer env.deinit();
    const src =
        \\[providers.copilot]
        \\style = "openai_chat"
        \\base_url = "https://api.individual.githubcopilot.com"
        \\auth = "k"
        \\model_catalog_name = "github-copilot"
        \\
        \\[auth.k]
        \\key = "tok"
    ;
    const doc = try parseDoc(a, src);
    defer doc.deinit();
    var cfg = try resolve(a, &env, doc.root);
    defer cfg.deinit();

    try testing.expectEqualStrings("github-copilot", cfg.provider("copilot").?.model_catalog_name.?);
}

test "resolve: openai_responses codex dialect maps to internal API style" {
    const a = testing.allocator;
    var env = emptyEnv(a);
    defer env.deinit();
    const src =
        \\[providers.codex]
        \\style = "openai_responses"
        \\dialect = "codex"
        \\base_url = "https://chatgpt.com/backend-api"
        \\auth = "k"
        \\
        \\[auth.k]
        \\key = "tok"
    ;
    const doc = try parseDoc(a, src);
    defer doc.deinit();
    var cfg = try resolve(a, &env, doc.root);
    defer cfg.deinit();

    try testing.expectEqual(APIStyle.openai_codex_responses, cfg.provider("codex").?.style);
    var defs = models_toml.ModelRegistry.init(a);
    defer defs.deinit();
    const pc = try buildProviderConfig(&cfg, &defs, .{ .provider = "codex", .model = "gpt-5.5" });
    try testing.expectEqual(APIStyle.openai_codex_responses, pc.style());
}

test "resolve: internal openai_codex_responses style is not user-facing" {
    const a = testing.allocator;
    var env = emptyEnv(a);
    defer env.deinit();
    const src =
        \\[providers.codex]
        \\style = "openai_codex_responses"
        \\base_url = "https://chatgpt.com/backend-api"
        \\auth = "k"
        \\
        \\[auth.k]
        \\key = "tok"
    ;
    const doc = try parseDoc(a, src);
    defer doc.deinit();
    try testing.expectError(error.InvalidProvider, resolve(a, &env, doc.root));
}

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"
        \\auth = "k"
        \\
        \\[providers.anthropic_nocache]
        \\style = "anthropic_messages"
        \\base_url = "https://api.anthropic.com"
        \\auth = "k"
        \\prompt_cache = false
        \\
        \\[auth.k]
        \\type = "api_key"
        \\key = "sk-ant"
    ;
    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: anthropic oauth_device uses bearer auth" {
    const a = testing.allocator;
    var env = emptyEnv(a);
    defer env.deinit();
    const src =
        \\[providers.copilot_anthropic]
        \\style = "anthropic_messages"
        \\base_url = "https://api.individual.githubcopilot.com"
        \\auth = "github_copilot"
        \\
        \\[auth.github_copilot]
        \\type = "oauth_device"
        \\client_id = "Iv1.x"
        \\device_code_url = "https://github.com/login/device/code"
        \\token_url = "https://github.com/login/oauth/access_token"
    ;
    var cfg = try loadFromString(a, &env, src);
    defer cfg.deinit();
    var defs = models_toml.ModelRegistry.init(a);
    defer defs.deinit();
    const pc = try buildProviderConfig(&cfg, &defs, .{ .provider = "copilot_anthropic", .model = "claude-sonnet-4-5" });
    try testing.expectEqual(APIStyle.anthropic_messages, pc.style());
    try testing.expect(pc.anthropic_messages.use_bearer_auth);
}

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"
        \\auth = "k"
        \\prompt_cache = false
        \\
        \\[auth.k]
        \\type = "api_key"
        \\key = "sk-ant"
    ;
    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: unknown default-model provider is an error" {
    const a = testing.allocator;
    var env = emptyEnv(a);
    defer env.deinit();

    const src =
        \\[defaults]
        \\model = "ghost:some-model"
    ;
    const doc = try parseDoc(a, src);
    defer doc.deinit();

    try testing.expectError(error.UnknownDefaultProvider, resolve(a, &env, doc.root));
}

test "resolvePolicy: pattern in both allow and deny is a conflict" {
    const a = testing.allocator;
    var env = emptyEnv(a);
    defer env.deinit();

    const src =
        \\[tools]
        \\allow = ["std.*"]
        \\deny = ["std.*"]
    ;
    const doc = try parseDoc(a, src);
    defer doc.deinit();

    try testing.expectError(error.PolicyConflict, resolve(a, &env, doc.root));
}

test "loadFromPaths: layers merge with tables accumulating and scalars overriding" {
    const a = testing.allocator;
    const io = testing.io;

    var tmp = testing.tmpDir(.{});
    defer tmp.cleanup();
    var path_buf: [std.fs.max_path_bytes]u8 = undefined;
    const tmp_n = try tmp.dir.realPath(io, &path_buf);
    const tmp_path = path_buf[0..tmp_n];

    // Base layer: defines anthropic provider + a default model.
    const sys_path = try std.fs.path.join(a, &.{ tmp_path, "base.toml" });
    defer a.free(sys_path);
    try tmp.dir.writeFile(io, .{ .sub_path = "base.toml", .data =
        \\[defaults]
        \\model = "anthropic:sonnet"
        \\
        \\[providers.anthropic]
        \\style = "anthropic_messages"
        \\base_url = "https://api.anthropic.com"
        \\auth = "anthropic_api"
        \\
        \\[auth.anthropic_api]
        \\type = "api_key"
        \\key = "sys-key"
        \\
        \\[tools]
        \\allow = ["std.*"]
    });

    // Project layer: adds an openai provider (table accumulates), and
    // overrides the default model (scalar overwrites).
    const proj_path = try std.fs.path.join(a, &.{ tmp_path, "project.toml" });
    defer a.free(proj_path);
    try tmp.dir.writeFile(io, .{ .sub_path = "project.toml", .data =
        \\[defaults]
        \\model = "openai:gpt"
        \\
        \\[providers.openai]
        \\style = "openai_chat"
        \\base_url = "https://api.openai.com/v1"
        \\auth = "openai_api"
        \\
        \\[auth.openai_api]
        \\type = "api_key"
        \\key = "proj-key"
    });

    var env = emptyEnv(a);
    defer env.deinit();

    var cfg = try loadFromPaths(a, io, &env, &.{ sys_path, proj_path });
    defer cfg.deinit();

    // Both providers survive (table accumulation).
    try testing.expectEqual(@as(usize, 2), cfg.providers.len);
    try testing.expect(cfg.provider("anthropic") != null);
    try testing.expect(cfg.provider("openai") != null);

    // Default model overridden by the project layer.
    try testing.expectEqualStrings("openai:gpt", cfg.default_model.?);
    try testing.expectEqualStrings("openai", cfg.default_model_ref.?.provider);
    try testing.expectEqualStrings("gpt", cfg.default_model_ref.?.model);

    // tools.allow from the base layer is preserved (no project override).
    try testing.expect(cfg.tools.permits("std.read"));
}

test "loadFromPaths: local layer overrides project layer" {
    const a = testing.allocator;
    const io = testing.io;

    var tmp = testing.tmpDir(.{});
    defer tmp.cleanup();
    var path_buf: [std.fs.max_path_bytes]u8 = undefined;
    const tmp_n = try tmp.dir.realPath(io, &path_buf);
    const tmp_path = path_buf[0..tmp_n];

    // Project layer: shared default model + provider.
    const proj_path = try std.fs.path.join(a, &.{ tmp_path, "project.toml" });
    defer a.free(proj_path);
    try tmp.dir.writeFile(io, .{ .sub_path = "project.toml", .data =
        \\[defaults]
        \\model = "openai:gpt"
        \\
        \\[providers.openai]
        \\style = "openai_chat"
        \\base_url = "https://api.openai.com/v1"
        \\auth = "openai_api"
        \\
        \\[auth.openai_api]
        \\type = "api_key"
        \\key = "proj-key"
    });

    // Local layer (git-ignored): a developer's more-opinionated override of
    // the default model. Scalar overwrites; the provider table accumulates.
    const local_path = try std.fs.path.join(a, &.{ tmp_path, "local.toml" });
    defer a.free(local_path);
    try tmp.dir.writeFile(io, .{ .sub_path = "local.toml", .data =
        \\[defaults]
        \\model = "openai:gpt-local"
    });

    var env = emptyEnv(a);
    defer env.deinit();

    var cfg = try loadFromPaths(a, io, &env, &.{ proj_path, local_path });
    defer cfg.deinit();

    // Local layer wins for the default model.
    try testing.expectEqualStrings("openai:gpt-local", cfg.default_model.?);
    // Provider from the project layer survives (table accumulation).
    try testing.expect(cfg.provider("openai") != null);
}

test "buildProviderConfig: anthropic ref pulls knobs from model defs" {
    const a = testing.allocator;
    var env = emptyEnv(a);
    defer env.deinit();
    try env.put("ANTHROPIC_API_KEY", "sk-ant");

    const doc = try parseDoc(a, anthropic_env_src);
    defer doc.deinit();
    var cfg = try resolve(a, &env, doc.root);
    defer cfg.deinit();

    var models = models_toml.ModelRegistry.init(a);
    defer models.deinit();
    try models.entries.append(a, .{
        .provider = try a.dupe(u8, "anthropic"),
        .alias = try a.dupe(u8, "sonnet"),
        .model = try a.dupe(u8, "claude-sonnet-4-20250514"),
        .reasoning = .high,
        .max_tokens = 8192,
        .api_version = try a.dupe(u8, "2023-06-01"),
        .thinking = .enabled,
        .effort = .medium,
        .thinking_budget_tokens = 16_000,
        .thinking_interleaved = false,
    });

    const ref = try parseModelRef("anthropic:sonnet");
    const pc = try buildProviderConfig(&cfg, &models, ref);
    try testing.expectEqual(APIStyle.anthropic_messages, pc.style());
    try testing.expectEqualStrings("claude-sonnet-4-20250514", pc.anthropic_messages.model);
    try testing.expectEqual(@as(u32, 8192), pc.anthropic_messages.max_tokens);
    try testing.expectEqualStrings("sk-ant", pc.anthropic_messages.api_key);
    try testing.expectEqual(panto.Thinking.enabled, pc.anthropic_messages.thinking);
    try testing.expectEqual(panto.Effort.medium, pc.anthropic_messages.effort);
    try testing.expectEqual(@as(?u32, 16_000), pc.anthropic_messages.thinking_budget_tokens);
    try testing.expectEqual(false, pc.anthropic_messages.thinking_interleaved);
}

test "buildProviderConfig: missing alias uses the alias verbatim as wire model" {
    const a = testing.allocator;
    var env = emptyEnv(a);
    defer env.deinit();

    const src =
        \\[providers.openai]
        \\style = "openai_chat"
        \\base_url = "https://api.openai.com/v1"
        \\auth = "k"
        \\
        \\[auth.k]
        \\type = "api_key"
        \\key = "sk-test"
    ;
    const doc = try parseDoc(a, src);
    defer doc.deinit();
    var cfg = try resolve(a, &env, doc.root);
    defer cfg.deinit();

    var models = models_toml.ModelRegistry.init(a);
    defer models.deinit();

    const ref = try parseModelRef("openai:gpt-4o");
    const pc = try buildProviderConfig(&cfg, &models, ref);
    try testing.expectEqual(APIStyle.openai_chat, pc.style());
    try testing.expectEqualStrings("gpt-4o", pc.openai_chat.model);
    try testing.expectEqual(panto.ReasoningEffort.default, pc.openai_chat.reasoning);
}

test "buildProviderConfig: anthropic adaptive thinking threaded from model def" {
    const a = testing.allocator;
    var env = emptyEnv(a);
    defer env.deinit();
    try env.put("ANTHROPIC_API_KEY", "sk-ant");

    const doc = try parseDoc(a, anthropic_env_src);
    defer doc.deinit();
    var cfg = try resolve(a, &env, doc.root);
    defer cfg.deinit();

    var models = models_toml.ModelRegistry.init(a);
    defer models.deinit();
    try models.entries.append(a, .{
        .provider = try a.dupe(u8, "anthropic"),
        .alias = try a.dupe(u8, "opus"),
        .model = try a.dupe(u8, "claude-opus-4-8"),
        .reasoning = .default,
        .max_tokens = null,
        .api_version = null,
        .thinking = .adaptive,
        .effort = .high,
        .thinking_budget_tokens = null,
        .thinking_interleaved = false,
    });

    const ref = try parseModelRef("anthropic:opus");
    const pc = try buildProviderConfig(&cfg, &models, ref);
    try testing.expectEqual(panto.Thinking.adaptive, pc.anthropic_messages.thinking);
    try testing.expectEqual(panto.Effort.high, pc.anthropic_messages.effort);
    try testing.expectEqual(@as(?u32, null), pc.anthropic_messages.thinking_budget_tokens);
}

test "buildProviderConfig: anthropic missing alias falls back to struct defaults" {
    const a = testing.allocator;
    var env = emptyEnv(a);
    defer env.deinit();
    try env.put("ANTHROPIC_API_KEY", "sk-ant");

    const doc = try parseDoc(a, anthropic_env_src);
    defer doc.deinit();
    var cfg = try resolve(a, &env, doc.root);
    defer cfg.deinit();

    var models = models_toml.ModelRegistry.init(a);
    defer models.deinit();

    // No model def at all — alias used verbatim, defaults applied.
    const ref = try parseModelRef("anthropic:claude-haiku-4-5-20251001");
    const pc = try buildProviderConfig(&cfg, &models, ref);
    try testing.expectEqual(APIStyle.anthropic_messages, pc.style());
    try testing.expectEqual(panto.Thinking.disabled, pc.anthropic_messages.thinking);
    try testing.expectEqual(panto.Effort.medium, pc.anthropic_messages.effort);
    try testing.expectEqual(@as(?u32, 32_000), pc.anthropic_messages.thinking_budget_tokens);
    try testing.expectEqual(false, pc.anthropic_messages.thinking_interleaved);
}

test "buildProviderConfig: unknown provider errors" {
    const a = testing.allocator;
    var env = emptyEnv(a);
    defer env.deinit();
    const empty = try parseDoc(a, "");
    defer empty.deinit();
    var cfg = try resolve(a, &env, empty.root);
    defer cfg.deinit();
    var models = models_toml.ModelRegistry.init(a);
    defer models.deinit();
    try testing.expectError(error.UnknownProvider, buildProviderConfig(&cfg, &models, .{ .provider = "ghost", .model = "x" }));
}

test "selectModel: default_model wins; single-provider fallback otherwise" {
    const a = testing.allocator;
    var env = emptyEnv(a);
    defer env.deinit();

    // Config with one provider and a default model.
    const src =
        \\[defaults]
        \\model = "openai:gpt"
        \\
        \\[providers.openai]
        \\style = "openai_chat"
        \\base_url = "https://api.openai.com/v1"
        \\auth = "k"
        \\
        \\[auth.k]
        \\type = "api_key"
        \\key = "sk"
    ;
    const doc = try parseDoc(a, src);
    defer doc.deinit();
    var cfg = try resolve(a, &env, doc.root);
    defer cfg.deinit();

    var models = models_toml.ModelRegistry.init(a);
    defer models.deinit();

    const ref = try cfg.selectModel(&models, null);
    try testing.expectEqualStrings("openai", ref.provider);
    try testing.expectEqualStrings("gpt", ref.model);

    // Override beats default.
    const ref2 = try cfg.selectModel(&models, "openai:other");
    try testing.expectEqualStrings("other", ref2.model);
}

test "selectModel: no default and no providers errors" {
    const a = testing.allocator;
    var env = emptyEnv(a);
    defer env.deinit();
    const empty = try parseDoc(a, "");
    defer empty.deinit();
    var cfg = try resolve(a, &env, empty.root);
    defer cfg.deinit();
    var models = models_toml.ModelRegistry.init(a);
    defer models.deinit();
    try testing.expectError(error.NoModelSelected, cfg.selectModel(&models, null));
}

test "loadFromPaths: missing files are skipped" {
    const a = testing.allocator;
    const io = testing.io;
    var env = emptyEnv(a);
    defer env.deinit();

    var cfg = try loadFromPaths(a, io, &env, &.{
        "/nonexistent/base.toml",
        "/nonexistent/project.toml",
    });
    defer cfg.deinit();
    try testing.expectEqual(@as(usize, 0), cfg.providers.len);
    try testing.expect(cfg.default_model == null);
}

test "resolve: [compaction] keep_verbatim and model parse" {
    const a = testing.allocator;
    var env = emptyEnv(a);
    defer env.deinit();
    try env.put("ANTHROPIC_API_KEY", "sk-ant-xyz");

    const src = anthropic_env_src ++
        \\
        \\[compaction]
        \\keep_verbatim = 12345
        \\model = "anthropic:haiku"
    ;
    const doc = try parseDoc(a, src);
    defer doc.deinit();

    var cfg = try resolve(a, &env, doc.root);
    defer cfg.deinit();
    try testing.expectEqual(@as(?u32, 12345), cfg.compaction_keep_verbatim);
    try testing.expectEqualStrings("anthropic:haiku", cfg.compaction_model.?);
    try testing.expectEqualStrings("anthropic", cfg.compaction_model_ref.?.provider);
    try testing.expectEqualStrings("haiku", cfg.compaction_model_ref.?.model);
}

test "resolve: [compaction] absent leaves defaults null" {
    const a = testing.allocator;
    var env = emptyEnv(a);
    defer env.deinit();
    try env.put("ANTHROPIC_API_KEY", "sk-ant-xyz");

    const doc = try parseDoc(a, anthropic_env_src);
    defer doc.deinit();

    var cfg = try resolve(a, &env, doc.root);
    defer cfg.deinit();
    try testing.expect(cfg.compaction_keep_verbatim == null);
    try testing.expect(cfg.compaction_model == null);
    try testing.expect(cfg.compaction_model_ref == null);
}

test "resolve: [compaction] model naming an unresolved provider errors" {
    const a = testing.allocator;
    var env = emptyEnv(a);
    defer env.deinit();
    try env.put("ANTHROPIC_API_KEY", "sk-ant-xyz");

    const src = anthropic_env_src ++
        \\
        \\[compaction]
        \\model = "openai:gpt-4o"
    ;
    const doc = try parseDoc(a, src);
    defer doc.deinit();

    try testing.expectError(error.UnknownDefaultProvider, resolve(a, &env, doc.root));
}