const std = @import("std");
const panto = @import("panto");
const pricing_format = @import("pricing_format.zig");
const markdown = @import("markdown.zig");
const lua_bridge = @import("lua_bridge.zig");
const lua_runtime = @import("lua_runtime.zig");
const lua_event_bridge = @import("lua_event_bridge.zig");
const extension_loader = @import("extension_loader.zig");
const panto_home = @import("panto_home.zig");
const luarocks_runtime = @import("luarocks_runtime.zig");
const subcommand = @import("subcommand.zig");
const session_paths = @import("session_paths.zig");
const models_toml = @import("models_toml.zig");
const config_file = @import("config_file.zig");
const auth_manager = @import("auth_manager.zig");
const glob = @import("glob.zig");
const system_prompt = @import("system_prompt.zig");
const command = @import("command.zig");
const command_compaction = @import("compaction.zig");
const builtin_commands = @import("builtin_commands.zig");
const debug_log = @import("debug_log.zig");

/// Route the process-wide log stream. `PANTO_DEBUG!=0` redirects it to a
/// per-session file; otherwise this keeps the stderr default.
pub const std_options: std.Options = .{ .logFn = debug_log.logFn };

// TUI foundation layer (Phase 1, sub-phase 1). Not yet wired into the REPL;
// referenced here so `zig build test` type-checks and exercises them.
const tui_terminal = @import("tui_terminal.zig");
const tui_key = @import("tui_key.zig");
const tui_input = @import("tui_input.zig");
const tui_theme = @import("tui_theme.zig");
const tui_component = @import("tui_component.zig");
const tui_engine = @import("tui_engine.zig");
const tui_components = @import("tui_components.zig");
const tui_event = @import("tui_event.zig");
const tui_app = @import("tui_app.zig");
const tui_selectors = @import("tui_selectors.zig");

// Shorthand alias for the Lua C API. The bridge module owns the actual
// `@cImport`; we re-use it here so the smoke check uses identical types.
const lua = lua_bridge.c;

// `fflush(NULL)` flushes every open C-stdio stream; used to drain buffered
// luarocks output before restoring fd 1 after the print-mode bootstrap.
extern "c" fn fflush(stream: ?*anyopaque) c_int;

test {
    // Test contract: deliberate error-path tests should not produce visible
    // log output. Code logs at `.err` for genuine production failures and
    // `.warn` for expected-failure paths exercised by tests; the test
    // runner's logger gates on `std.testing.log_level`, which defaults to
    // `.warn`. Raising it to `.err` silences expected warnings without
    // changing production behavior. Anything that *should* be visible in a
    // passing test must use `std.debug.print` or assert via the testing API.
    std.testing.log_level = .err;

    std.testing.refAllDecls(@This());
    _ = lua_bridge;
    _ = lua_runtime;
    _ = lua_event_bridge;
    _ = extension_loader;
    _ = panto_home;
    _ = luarocks_runtime;
    _ = subcommand;
    _ = models_toml;
    _ = config_file;
    _ = auth_manager;
    _ = glob;
    _ = system_prompt;
    _ = command;
    _ = command_compaction;
    _ = builtin_commands;
    _ = debug_log;
    _ = pricing_format;
    _ = markdown;
    _ = tui_terminal;
    _ = tui_key;
    _ = tui_input;
    _ = tui_theme;
    _ = tui_component;
    _ = tui_engine;
    _ = tui_components;
    _ = tui_event;
    _ = tui_app;
    _ = tui_selectors;
}

/// Spin up a Lua interpreter, run a no-op, tear it down. Catches
/// link/compile errors on the Lua dependency at the earliest moment.
/// Logs only in debug builds; release builds run silently.
fn luaSmokeCheck() void {
    const L = lua.luaL_newstate() orelse {
        std.log.err("lua: luaL_newstate returned null", .{});
        return;
    };
    defer lua.lua_close(L);
    lua.luaL_openlibs(L);

    // Push _VERSION to confirm libs loaded.
    _ = lua.lua_getglobal(L, "_VERSION");
    const ver = lua.lua_tolstring(L, -1, null);
    if (ver != null) {
        std.log.debug("lua: {s} linked OK", .{ver});
    }
    lua.lua_settop(L, 0);
}

/// Print a friendly message for a config.toml load failure before the
/// process exits non-zero.
fn reportConfigError(err: anyerror) void {
    switch (err) {
        error.InvalidConfigToml => std.debug.print(
            "error: a config.toml failed to parse (see log above).\n",
            .{},
        ),
        error.InvalidProvider => std.debug.print(
            "error: a [providers.*] entry is malformed (need style + base_url).\n",
            .{},
        ),
        error.InvalidModelRef => std.debug.print(
            "error: defaults.model must look like \"provider:model\".\n",
            .{},
        ),
        error.UnknownDefaultProvider => std.debug.print(
            "error: defaults.model names a provider that isn't configured (or whose API key env var isn't set).\n",
            .{},
        ),
        error.PolicyConflict => std.debug.print(
            "error: a tool/extension pattern appears in both allow and deny.\n",
            .{},
        ),
        error.NoHomeDirectory => std.debug.print(
            "error: cannot resolve config paths — set HOME or XDG_CONFIG_HOME/XDG_DATA_HOME.\n",
            .{},
        ),
        else => std.debug.print("error: failed to load config: {s}\n", .{@errorName(err)}),
    }
}

/// Print a friendly message for a model-selection failure.
fn reportModelError(err: anyerror, cfg: *const config_file.Config) void {
    switch (err) {
        error.NoModelSelected => {
            std.debug.print(
                "error: no model selected. Set `defaults.model = \"provider:alias\"` in config.toml.\n",
                .{},
            );
            if (cfg.providers.len == 0) {
                std.debug.print(
                    "  (no providers resolved — check that an API key or its env var is present.)\n",
                    .{},
                );
            }
        },
        error.UnknownProvider => std.debug.print(
            "error: the selected model names an unconfigured provider.\n",
            .{},
        ),
        error.UnknownModelAlias => std.debug.print(
            "error: --model matches no alias in models.toml. Use \"provider:alias\" or a known alias.\n",
            .{},
        ),
        error.AmbiguousModelAlias => std.debug.print(
            "error: --model alias exists under multiple providers; use \"provider:alias\".\n",
            .{},
        ),
        else => std.debug.print("error: model selection failed: {s}\n", .{@errorName(err)}),
    }
}

pub fn main(init: std.process.Init) !void {
    const alloc = init.gpa;
    const io = init.io;

    // Smoke test: prove Lua is linked. Slice 1 — no extension runtime
    // wired up yet, this just confirms the static lib comes through.
    luaSmokeCheck();

    // Resolve the absolute path of the running panto binary. Needed
    // both by `panto lua` (we re-exec ourselves through a wrapper
    // luarocks invokes) and by the agent's bootstrap.
    const panto_path = try std.process.executablePathAlloc(io, alloc);
    defer alloc.free(panto_path);

    // Subcommand dispatch: `panto lua` and `panto bootstrap` short
    // out of the agent loop, but still run the same luarocks bootstrap
    // pipeline so first-run setup happens consistently.
    switch (try subcommand.dispatch(
        alloc,
        io,
        init.environ_map,
        init.minimal.args,
        panto_path,
    )) {
        .done => return,
        .agent => {},
    }

    // Parse the agent-mode flags (`--resume [<id>]`, `-c/--continue`,
    // `-m/--model`, `--effort`). Unknown flags are fatal — a typo must not
    // launch the TUI.
    const cli_flags = try parseAgentFlags(alloc, init.minimal.args);
    defer cli_flags.deinit(alloc);

    var stdout_buffer: [4096]u8 = undefined;
    var stdout_file = std.Io.File.stdout().writer(io, &stdout_buffer);
    const stdout = &stdout_file.interface;

    // The TUI reads raw bytes from the tty fd directly (raw mode); we only
    // need the stdin file handle, not a buffered reader.
    const stdin_handle = std.Io.File.stdin().handle;

    // Resolve the print-mode prompt up front so a missing prompt fails fast,
    // before any bootstrap work: flag argument first, else piped stdin.
    var print_prompt_owned: ?[]u8 = null;
    defer if (print_prompt_owned) |p| alloc.free(p);
    const print_prompt: ?[]const u8 = if (!cli_flags.print_mode) null else blk: {
        if (cli_flags.print_prompt) |p| break :blk p;
        if (std.c.isatty(stdin_handle) != 0) {
            std.debug.print("error: -p/--print needs a prompt argument or piped stdin\n", .{});
            std.process.exit(1);
        }
        var stdin_buf: [4096]u8 = undefined;
        var stdin_reader = std.Io.File.stdin().readerStreaming(io, &stdin_buf);
        const raw = try stdin_reader.interface.allocRemaining(alloc, .unlimited);
        print_prompt_owned = raw;
        if (std.mem.trim(u8, raw, " \t\r\n").len == 0) {
            std.debug.print("error: -p/--print got an empty prompt on stdin\n", .{});
            std.process.exit(1);
        }
        break :blk raw;
    };

    // Resolve where this project's sessions live.
    var cwd_buf: [std.fs.max_path_bytes]u8 = undefined;
    const cwd_n = try std.process.currentPath(io, &cwd_buf);
    const cwd = cwd_buf[0..cwd_n];
    const session_dir = try session_paths.sessionDirForCwd(alloc, init.environ_map, cwd);
    defer alloc.free(session_dir);

    // Load the merged config.toml (base → user → project). Providers,
    // default model, and tool/extension policy all come from here.
    var app_config = config_file.load(alloc, io, init.environ_map, cwd) catch |err| {
        reportConfigError(err);
        std.process.exit(1);
    };
    defer app_config.deinit();

    // Load models.toml — model aliases (wire name + knobs) and pricing —
    // merged across the base/user/project/local layers. Missing files are
    // fine (empty registries); cost lookups return null, formatted as
    // "unknown" by the display layer.
    var models = try models_toml.load(alloc, io, init.environ_map, cwd);
    defer models.deinit();
    std.log.debug(
        "models.toml: {d} model def(s), {d} price entr(ies) from merged layers",
        .{ models.defs.count(), models.pricing.count() },
    );
    // `models.pricing` is parsed and ready; the print-based CLI doesn't
    // surface per-turn cost yet (that lands with the TUI frontend).

    // Choose the active model and assemble the provider config.
    const model_ref = app_config.selectModel(&models.defs, cli_flags.model) catch |err| {
        reportModelError(err, &app_config);
        std.process.exit(1);
    };
    var provider_config = config_file.buildProviderConfig(&app_config, &models.defs, model_ref) catch |err| {
        reportModelError(err, &app_config);
        std.process.exit(1);
    };

    // Reasoning-level precedence: `--effort` beats everything; otherwise a
    // `[defaults] reasoning` session default applies unless models.toml set
    // an explicit per-alias knob (which `buildProviderConfig` already baked
    // in). Levels are the Ctrl+R picker's labels for the provider's style.
    const effort_label: ?[]const u8 = cli_flags.effort orelse blk: {
        if (models.defs.get(model_ref.provider, model_ref.model)) |d| {
            if (d.reasoning_explicit) break :blk null;
        }
        break :blk app_config.default_reasoning;
    };
    if (effort_label) |lvl| {
        if (tui_selectors.ReasoningOption.byLabel(provider_config.style(), lvl)) |opt| {
            opt.apply(&provider_config);
        } else if (cli_flags.effort != null) {
            std.debug.print("error: --effort '{s}' is not a reasoning level for this provider (available:", .{lvl});
            for (tui_selectors.ReasoningOption.forStyle(provider_config.style())) |opt| {
                std.debug.print(" {s}", .{opt.label});
            }
            std.debug.print(")\n", .{});
            std.process.exit(1);
        } else {
            std.log.warn("[defaults] reasoning '{s}' has no such level on this provider; ignored", .{lvl});
        }
    }

    // Resolve the optional compaction-model override into a ProviderConfig.
    // On any resolution failure we log and fall back to no override (the
    // active chat model is used for compaction).
    const compaction_provider_config: ?panto.ProviderConfig = blk: {
        const ref = app_config.compaction_model_ref orelse break :blk null;
        break :blk config_file.buildProviderConfig(&app_config, &models.defs, ref) catch |err| {
            std.log.warn("compaction_model resolution failed ({t}); using active model", .{err});
            break :blk null;
        };
    };
    const compaction_cfg: panto.CompactionConfig = .{
        .keep_verbatim = app_config.compaction_keep_verbatim orelse 20_000,
        .model = compaction_provider_config,
    };

    // Process-global HTTP client: one connection pool for every provider /
    // base_url the agent may switch to. Torn down at shutdown.
    panto.init(alloc, io);
    defer panto.deinit();

    const banner_model_initial: []const u8 = switch (provider_config) {
        inline else => |c| c.model,
    };
    const banner_provider_initial: []const u8 = model_ref.provider;

    // The session store: a directory-backed JSONL catalog rooted at the
    // per-cwd `session_dir` (the CLI owns the cwd→dir grouping; the store
    // is cwd-agnostic). Must outlive the agent, which appends through a
    // `Session` handle minted/resolved below.
    const cwd_json = try std.json.Stringify.valueAlloc(alloc, cwd, .{});
    defer alloc.free(cwd_json);
    const session_metadata = try std.fmt.allocPrint(alloc, "{{\"cwd\":{s}}}", .{cwd_json});
    defer alloc.free(session_metadata);
    var session_store_impl = try panto.FileSystemJSONLStore.initWithMetadata(alloc, io, session_dir, session_metadata);
    defer session_store_impl.deinit();
    const session_store = session_store_impl.store();

    // Create or resume the session. Resume failures (missing/ambiguous id)
    // are user errors — print a tidy message and exit 1 rather than
    // printing a Zig stack trace.
    var session = openSession(
        session_store,
        cli_flags,
        session_dir,
    ) catch |err| switch (err) {
        error.SessionNotFound, error.AmbiguousSessionId => std.process.exit(1),
        else => return err,
    };
    // `session.info` is adopted by the agent below (`Agent.init` can't fail)
    // and freed in the agent's `deinit`; no separate cleanup here.

    // Arm the per-session debug log now that we know the session id.
    // PANTO_DEBUG!=0 redirects `std.log` output to
    // `<data home>/debug/<id>.log`. Best-effort: failures leave normal
    // logging in place.
    debug_log.init(alloc, io, init.environ_map, session.info.id);

    const is_resume = cli_flags.resume_kind != .none and session.info.message_count > 0;

    // On resume, reconstruct the conversation from the store. (The
    // dangling-prompt recovery feature was dropped in R2.) On a fresh
    // session, the agent starts with an empty conversation.
    var adopted_conversation: ?panto.Conversation = null;
    if (is_resume) {
        adopted_conversation = try session.load();
        if (!cli_flags.print_mode) {
            const sid = session.info.id;
            try stdout.print(
                "resumed session {s} ({d} messages)\n",
                .{ sid[0..@min(8, sid.len)], session.info.message_count },
            );
        }
    }

    // The active configuration snapshot the agent (re-)reads each turn.
    var active_config: panto.Config = .{
        .provider = provider_config,
        .compaction = compaction_cfg,
    };

    // Resolve the panto data home layout up front: the agent-tree dir feeds
    // system-prompt sourcing (below) and the auth dir feeds the AuthManager.
    var home_layout = try panto_home.resolve(alloc, init.environ_map);
    defer home_layout.deinit();

    // Process-level luarocks runtime: stage the rocks/agent trees once and
    // keep a dedicated driver `lua_State` for luarocks work (battery
    // reconcile, `extensions.rocks` installs). Session interpreters are
    // disposable (/new, /resume rebuild them), so the driver state must not
    // ride on one of them. `--no-extensions` skips all of it: built-ins
    // only, and since even the shipped tools are extensions the agent runs
    // with no tools — the escape hatch when an extension breaks startup.
    var luarocks_L: ?*lua.lua_State = null;
    defer if (luarocks_L) |L| lua.lua_close(L);
    var luarocks_rt: ?*luarocks_runtime.LuarocksRuntime = null;
    defer if (luarocks_rt) |lr| lr.deinit();
    // In print mode, shunt fd 1 to stderr for the whole extension bootstrap:
    // luarocks (first-run bootstrap, rock installs) prints compile/progress
    // output to stdout via C stdio, which would pollute the scripted `-p`
    // output. Restored below, before the print turn writes assistant text.
    const saved_stdout: ?std.c.fd_t = if (cli_flags.print_mode and !cli_flags.no_extensions) blk: {
        try stdout_file.flush();
        const saved = std.c.dup(std.posix.STDOUT_FILENO);
        if (saved == -1) break :blk null;
        if (std.c.dup2(std.posix.STDERR_FILENO, std.posix.STDOUT_FILENO) == -1) {
            _ = std.c.close(saved);
            break :blk null;
        }
        break :blk saved;
    } else null;
    if (!cli_flags.no_extensions) {
        const L = lua.luaL_newstate() orelse return error.OutOfMemory;
        luarocks_L = L;
        lua.luaL_openlibs(L);

        // Bootstrap luarocks — same pipeline as `panto lua` and `panto
        // bootstrap`. After this, `require("luarocks.*")` works on the
        // driver state and any pinned batteries from the manifest are
        // installed under the panto data home.
        luarocks_rt = try luarocks_runtime.bootstrap(
            alloc,
            io,
            init.environ_map,
            L,
            panto_path,
        );

        // Install any user rocks (`extensions.rocks`) into the shared tree
        // so extension loading can `require` them. Best-effort: a rock that
        // fails to install is logged and skipped — the REPL still starts.
        // This is where registry code enters, so it is the code-execution
        // trust boundary; the allow/deny policy is a feature toggle, not a
        // security gate.
        for (app_config.ext_rocks) |spec| {
            _ = luarocks_runtime.installRockIfMissing(luarocks_rt.?, alloc, io, spec.value) catch |err| {
                std.log.err("extensions.rocks: failed to install '{s}': {t}", .{ spec.value, err });
            };
        }
    }

    // Base layer for system-prompt sourcing. With extensions on, the
    // bootstrap above staged the bundled agent tree (incl. SYSTEM.md) there;
    // with `--no-extensions` the path may not exist — missing prompt files
    // are simply skipped, and user/project layers still apply.
    const agent_dir = if (luarocks_rt) |lr| lr.layout.agent_dir else home_layout.agent_dir;

    // Slash-command registry: process-lifetime. Builtins register once
    // here; Lua-extension commands are harvested into it by each world
    // build (and removed again at world teardown).
    var cmd_registry = command.Registry.init(alloc);
    defer cmd_registry.deinit();
    try command_compaction.register(&cmd_registry);
    try builtin_commands.register(&cmd_registry);

    // Build the per-session world — Agent + Lua interpreter + derived
    // system/compaction prompts — through the exact code path `/new` and
    // `/resume` rebuild it (see `SessionWorld`). Declared before the TUI so
    // the App tears down first (the teardown ordering contract below).
    var world: SessionWorld = .{
        .alloc = alloc,
        .io = io,
        .environ = init.environ_map,
        .app_config = &app_config,
        .active_config = &active_config,
        .agent_dir = agent_dir,
        .luarocks_rt = luarocks_rt,
        .registry = &cmd_registry,
    };
    defer world.deinit();
    try world.build(session, adopted_conversation);
    const agent = world.agent.?;

    // Point fd 1 back at the real stdout (see the dup above). Drain the C
    // stdio buffer first so buffered luarocks output flushes to stderr, not
    // into the restored stdout at exit.
    if (saved_stdout) |fd| {
        _ = fflush(null);
        _ = std.c.dup2(fd, std.posix.STDOUT_FILENO);
        _ = std.c.close(fd);
    }

    // Command output is captured into an in-memory buffer (the command
    // Context's `stdout`) and flushed into the TUI transcript after each
    // dispatch — TUI-safe: handlers never write raw bytes mid-frame. This is
    // the documented minimal choice for slash-command output under the TUI; a
    // richer routing (per-command transcript components) can refine it later.
    var cmd_capture = std.Io.Writer.Allocating.init(alloc);
    defer cmd_capture.deinit();

    var cmd_ctx: command.Context = .{
        .allocator = alloc,
        .agent = agent,
        .stdout = &cmd_capture.writer,
        .stdout_file = &stdout_file,
        .compaction_prompt = world.compaction_prompt,
        .provider_name = banner_provider_initial,
        .model_name = banner_model_initial,
        .lua_rt = world.rt,
        .session_store = session_store,
        // `.tui` is installed after TUI bring-up below; null in print mode.
    };

    // Turn-time auth resolution. The manager resolves the active provider's
    // named auth session (api_key: no-op; oauth_device: refresh/exchange or an
    // interactive device login) into the live config before each turn.
    var auth_mgr = auth_manager.AuthManager.init(
        alloc,
        io,
        panto.httpClient(),
        home_layout.auth_dir,
        &app_config,
    );
    defer auth_mgr.deinit();

    // -- Print mode (-p/--print) -------------------------------------------
    //
    // One agent turn (tools and all) without the TUI: assistant text to
    // stdout, errors to stderr, exit 0/1. Session persistence is identical to
    // the TUI path — the agent owns it.
    if (cli_flags.print_mode) {
        runPrintTurn(
            alloc,
            agent,
            &active_config,
            model_ref.provider,
            &auth_mgr,
            &stdout_file,
            print_prompt.?,
        ) catch |err| {
            std.debug.print("error: turn failed: {t}\n", .{err});
            std.process.exit(1);
        };
        return;
    }

    // -- TUI bring-up ------------------------------------------------------
    //
    // Full replacement of the print REPL (version control is the safety net).
    // The terminal enters raw mode + bracketed paste; the engine drives a
    // differential render of the transcript + pinned input box + footer; the
    // app loop pumps libpanto's pull Stream into component state. The terminal
    // is restored on every exit path (defer) and on crash (signal handlers
    // installed by `enableRawMode` + the panic-restore hook).
    var term = tui_terminal.Terminal.init(stdin_handle, init.environ_map.*) catch |err| switch (err) {
        tui_terminal.Error.NotATty => {
            std.debug.print(
                "error: panto's TUI requires an interactive terminal (stdin/stdout must be a tty).\n",
                .{},
            );
            std.process.exit(1);
        },
        else => return err,
    };
    try term.enableRawMode();
    defer term.deinit();

    const size = term.refreshSize();
    var tui_writer_buf: [16 * 1024]u8 = undefined;
    var tui_file = std.Io.File.stdout().writer(io, &tui_writer_buf);
    var engine = tui_engine.Engine.init(
        alloc,
        &tui_file.interface,
        size.cols,
        size.rows,
        term.caps.synchronized_output,
    );
    defer engine.deinit();

    var input_box = tui_components.InputBox.init(alloc);
    defer input_box.deinit();
    var footer = tui_components.Footer.init(alloc);
    defer footer.deinit();

    var io_clock = tui_app.IoClock.init(io);
    var app = tui_app.App.init(
        alloc,
        &engine,
        io_clock.clock(),
        &input_box,
        &footer,
    );
    defer app.deinit();

    // `[tui] tools_collapsed`: the Ctrl+O collapse state's starting value.
    if (app_config.tui_tools_collapsed) |c| app.tools_collapsed = c;

    // Footer: the model's context window (for the fractional context
    // readout; null = raw count). The session short-id is stamped by
    // `rebuild_host.wire()` below.
    if (models.defs.get(model_ref.provider, model_ref.model)) |d| {
        footer.setContextWindow(d.context_window);
    }

    // TUI-steering slash commands (/model, /reasoning, /new, /quit) reach
    // the live App through the command Context (opaque, same idiom as
    // `lua_rt`); the pointer is stable for the whole run loop.
    cmd_ctx.tui = &app;

    // The Lua extension UI event bridge (bus handlers + override-release
    // hook) is wired to the App by `rebuild_host.wire()` below — the same
    // call the mid-run /new//resume rebuild uses.
    //
    // TEARDOWN ORDERING CONTRACT (load-bearing — do not reorder these decls):
    //   `app` is declared AFTER `world`, so `defer app.deinit()` runs BEFORE
    //   `defer world.deinit()` (defers are LIFO). The bridge (owned by the
    //   world's Lua runtime) therefore outlives the App's teardown. This
    //   matters because the release hook points into the bridge: if the
    //   bridge were freed first, any later hook invocation would be a
    //   use-after-free. It is safe today because `App.deinit` frees only its
    //   own default `kind` boxes and NEVER invokes `override_release_fn` —
    //   the surviving (non-superseded) Lua overrides are freed by
    //   `EventBridge.deinit` when the world tears its runtime down. The hook
    //   fires only during live mid-stream swaps, while both App and bridge
    //   are alive. A mid-run `/new`//`/resume` rebuild inverts the order (the
    //   runtime dies while the App lives), which is why `RebuildHost.rebuild`
    //   calls `app.resetSessionUi()` — dropping every transcript entry, bus
    //   handler, and this hook — BEFORE `world.deinit()`. If you ever make
    //   `App.deinit` call the release hook, or move the world to outlive
    //   `app`, revisit this.

    const Flusher = struct {
        fn flush(ctx: *anyopaque) void {
            const fw: *std.Io.File.Writer = @ptrCast(@alignCast(ctx));
            fw.interface.flush() catch {};
        }
    };
    app.setFlusher(&tui_file, Flusher.flush);

    const model_label = try std.fmt.allocPrint(
        alloc,
        "{s}:{s}",
        .{ banner_provider_initial, banner_model_initial },
    );
    defer alloc.free(model_label);

    // Runtime model/reasoning selectors (Ctrl+T / Ctrl+R). Live-session only:
    // a pick rebuilds the provider config and pushes it to the agent via
    // `setConfig`; nothing is written back to config.toml. Borrows the
    // long-lived `app_config`, `models.defs`, and `active_config`.
    const selector_ctrl = try tui_app.SelectorController.init(
        alloc,
        &app,
        agent,
        &app_config,
        &models.defs,
        &models.pricing,
        &active_config,
        model_label,
    );
    defer selector_ctrl.deinit();
    // Command-completion popup (leading-`/` typeahead) and the `/resume`
    // session picker read these; both are stable for the loop's lifetime.
    selector_ctrl.registry = &cmd_registry;
    selector_ctrl.session_store = session_store;
    app.setSelectors(selector_ctrl);

    // In-place session switching (/new, /resume): the host tears the world
    // down, rebuilds it through the boot path above, and repoints every
    // borrower of the old agent/runtime. Installed after all borrowers exist.
    var rebuild_host = RebuildHost{ .world = &world, .app = &app, .cmd_ctx = &cmd_ctx };
    try rebuild_host.wire();
    app.setSessionRebuild(&rebuild_host, RebuildHost.rebuild);

    // The render engine writes through a buffered file writer; flush after the
    // loop so the final frame and teardown sequences reach the terminal.
    defer tui_file.interface.flush() catch {};

    tui_app.runLoop(&app, &term, .{
        .cmd_registry = &cmd_registry,
        .cmd_ctx = &cmd_ctx,
        .cmd_capture = &cmd_capture,
        .model_label = model_label,
        .cwd = cwd,
        .io = io,
        .environ = init.environ_map,
        .editor_override = app_config.tui_editor,
        .auth_mgr = &auth_mgr,
    }) catch |err| switch (err) {
        // Clean user-initiated exit (Ctrl+C / Ctrl+D). Not an error.
        error.UserExit => {},
        else => {
            // Restore the terminal before surfacing the diagnostic so the
            // message is readable.
            term.deinit();
            tui_file.interface.flush() catch {};
            std.debug.print("\n[fatal: {s}]\n", .{@errorName(err)});
            return err;
        },
    };
}

// -----------------------------------------------------------------------------
// CLI flag parsing
// -----------------------------------------------------------------------------

const AgentFlags = struct {
    /// `--resume` without an id: resume the most recent session.
    /// `--resume <id>`: resume the session whose id has this prefix.
    /// Not present: start a new session.
    resume_kind: ResumeKind = .none,
    resume_id: ?[]const u8 = null, // owned
    /// `-m/--model <provider:alias>` (or a bare alias): model override.
    model: ?[]const u8 = null, // owned
    /// `--effort <level>`: reasoning-level override (the Ctrl+R picker's
    /// labels). Beats models.toml per-alias knobs and `[defaults] reasoning`.
    effort: ?[]const u8 = null, // owned
    /// `-p/--print [<prompt>]`: one-shot non-interactive mode. The prompt
    /// comes from the flag's argument, or from stdin when piped.
    print_mode: bool = false,
    print_prompt: ?[]const u8 = null, // owned
    /// `--no-extensions`: skip the Lua/luarocks runtime entirely (see bootstrap in main()).
    no_extensions: bool = false,

    pub fn deinit(self: AgentFlags, alloc: std.mem.Allocator) void {
        if (self.resume_id) |id| alloc.free(id);
        if (self.model) |m| alloc.free(m);
        if (self.effort) |e| alloc.free(e);
        if (self.print_prompt) |p| alloc.free(p);
    }
};

const ResumeKind = enum { none, most_recent, by_id };

fn parseAgentFlags(alloc: std.mem.Allocator, args: std.process.Args) !AgentFlags {
    var flags: AgentFlags = .{};
    errdefer flags.deinit(alloc);

    // Materialize argv so `--resume`'s optional-id lookahead can decline a
    // `-`-leading token without consuming it (the Args iterator can't rewind).
    var it = args.iterate();
    defer it.deinit();
    _ = it.next(); // argv[0]
    var argv: std.ArrayList([]const u8) = .empty;
    defer argv.deinit(alloc);
    while (it.next()) |a| try argv.append(alloc, a);

    var i: usize = 0;
    while (i < argv.items.len) : (i += 1) {
        const a = argv.items[i];
        if (std.mem.eql(u8, a, "--resume")) {
            flags.resume_kind = .most_recent;
            // An id follows only if the next token doesn't look like a flag.
            if (i + 1 < argv.items.len and argv.items[i + 1].len > 0 and argv.items[i + 1][0] != '-') {
                if (flags.resume_id) |old| alloc.free(old);
                flags.resume_id = try alloc.dupe(u8, argv.items[i + 1]);
                flags.resume_kind = .by_id;
                i += 1;
            }
            continue;
        }
        if (std.mem.eql(u8, a, "-c") or std.mem.eql(u8, a, "--continue")) {
            flags.resume_kind = .most_recent;
            continue;
        }
        if (std.mem.eql(u8, a, "-m") or std.mem.eql(u8, a, "--model")) {
            if (i + 1 >= argv.items.len) {
                std.debug.print("error: {s} requires a <provider:alias> argument\n", .{a});
                std.process.exit(1);
            }
            if (flags.model) |old| alloc.free(old);
            flags.model = try alloc.dupe(u8, argv.items[i + 1]);
            i += 1;
            continue;
        }
        if (std.mem.eql(u8, a, "--effort")) {
            if (i + 1 >= argv.items.len) {
                std.debug.print("error: --effort requires a <level> argument\n", .{});
                std.process.exit(1);
            }
            if (flags.effort) |old| alloc.free(old);
            flags.effort = try alloc.dupe(u8, argv.items[i + 1]);
            i += 1;
            continue;
        }
        if (std.mem.eql(u8, a, "-p") or std.mem.eql(u8, a, "--print")) {
            flags.print_mode = true;
            // An inline prompt follows only if the next token doesn't look
            // like a flag; otherwise the prompt comes from piped stdin.
            if (i + 1 < argv.items.len and argv.items[i + 1].len > 0 and argv.items[i + 1][0] != '-') {
                if (flags.print_prompt) |old| alloc.free(old);
                flags.print_prompt = try alloc.dupe(u8, argv.items[i + 1]);
                i += 1;
            }
            continue;
        }
        if (std.mem.eql(u8, a, "--no-extensions")) {
            flags.no_extensions = true;
            continue;
        }
        // Future agent-mode flags land here.
        std.debug.print("error: unknown argument '{s}' (run 'panto --help')\n", .{a});
        std.process.exit(1);
    }
    return flags;
}

// -----------------------------------------------------------------------------
// SessionWorld — per-session boot wiring
// -----------------------------------------------------------------------------

/// Everything whose lifetime IS the session: the Agent, the Lua interpreter,
/// and the arena feeding the derived system/compaction prompts. `/new` and
/// `/resume` are "quit and relaunch, minus the process": tear the world down
/// and `build` a fresh one through this exact code path — the same one boot
/// uses. Process-level state (config/models, HTTP client, session store,
/// luarocks tree + its driver `lua_State`, the TUI, auth) lives outside and
/// is borrowed via the fields below.
const SessionWorld = struct {
    // Borrowed process-level dependencies (valid for the process lifetime).
    alloc: std.mem.Allocator,
    io: std.Io,
    environ: *const std.process.Environ.Map,
    app_config: *const config_file.Config,
    /// The live config snapshot the agent reads; `build` stamps the
    /// re-resolved compaction prompt into it.
    active_config: *panto.Config,
    /// Base layer for system-prompt sourcing and extension discovery.
    agent_dir: []const u8,
    /// Non-null iff extensions are on (`--no-extensions` leaves it null and
    /// the world builds with a null Lua runtime). Supplies the per-state
    /// luarocks wiring (`attachState`) for each fresh interpreter.
    luarocks_rt: ?*luarocks_runtime.LuarocksRuntime,
    /// The process-lifetime slash-command registry. Builtins register once
    /// (in `main`); `build` harvests Lua commands into it and `deinit`
    /// removes exactly those again, so a rebuild never double-registers.
    registry: *command.Registry,

    // Owned per-session state. Null/empty between `deinit` and `build`, so
    // a failed rebuild leaves a world that is still safe to `deinit`.
    agent: ?*panto.Agent = null,
    rt: ?*lua_runtime.LuaRuntime = null,
    sp_arena: ?std.heap.ArenaAllocator = null,
    /// Resolved compaction prompt (owned by `sp_arena`).
    compaction_prompt: []const u8 = "",

    /// Build the world around `session`, adopting `conv` when resuming
    /// (boot's `--resume` and the `/resume` command both load the
    /// conversation from the store first and hand it here; `Agent.init`
    /// marks adopted history as already persisted, so nothing is re-written
    /// to disk). On error nothing is left allocated.
    fn build(self: *SessionWorld, session: panto.Session, conv: ?panto.Conversation) !void {
        std.debug.assert(self.agent == null and self.rt == null and self.sp_arena == null);
        const is_resume = conv != null;

        const agent = try panto.Agent.init(self.alloc, self.io, self.active_config, session, conv);
        errdefer agent.deinit();

        // One fresh interpreter per session: extensions may keep module-
        // global state, and its lifetime contract is exactly the session's
        // (see `extension_loader.zig`).
        var rt: ?*lua_runtime.LuaRuntime = null;
        errdefer if (rt) |r| r.deinit();
        if (self.luarocks_rt) |lr| {
            const r = try lua_runtime.LuaRuntime.create(self.alloc);
            rt = r;
            // Per-state luarocks wiring (embedded searcher, hardcoded
            // config, package.path/cpath) so `require` resolves the staged
            // `panto.so` and installed rocks. Disk staging happened once at
            // process bootstrap.
            try lr.attachState(r.L);
        }

        // Source the system prompt (SYSTEM.md / APPEND_SYSTEM.md across the
        // base/user/project layers): seed a fresh session, or reconcile a
        // resumed log without rewriting history.
        var arena = std.heap.ArenaAllocator.init(self.alloc);
        errdefer arena.deinit();
        if (is_resume) {
            try system_prompt.reconcileResume(arena.allocator(), self.io, self.environ, self.agent_dir, agent);
        } else {
            try system_prompt.seedFresh(arena.allocator(), self.io, self.environ, self.agent_dir, agent);
        }

        errdefer self.registry.clearLua();
        if (rt) |r| {
            // Wire `require('panto')` to the native module + `ext` subtable,
            // hand extensions the live session agent, then install the luv
            // scheduler — in that order (see each fn's doc).
            try r.installPantoModule();
            try r.setExtAgent(agent);
            try r.installScheduler();

            // Discover + activate Lua extensions across the base/user/
            // project layers; register their tools as one source.
            const n_ext_tools = extension_loader.discoverAndLoad(
                self.alloc,
                self.io,
                self.environ,
                self.agent_dir,
                r,
                &self.app_config.extensions,
                self.app_config.ext_paths,
                self.app_config.ext_rocks,
            ) catch |err| {
                std.log.err("extension discovery failed: {t}", .{err});
                return err;
            };
            std.log.debug("extensions: {d} tool(s) registered", .{n_ext_tools});
            if (n_ext_tools > 0) try agent.registerToolSource(r.toolSource());

            // Slash commands declared via `panto.ext.register_command`. A
            // name collision with a builtin (or between two extensions)
            // aborts, matching the tool-name collision policy.
            for (r.commandList()) |lua_cmd| {
                self.registry.registerLua(
                    lua_cmd.name,
                    lua_cmd.description,
                    lua_cmd.handler_ref,
                ) catch |err| {
                    std.log.err(
                        "lua: failed to register command '/{s}': {t}",
                        .{ lua_cmd.name, err },
                    );
                    return err;
                };
            }
        }

        // Resolve the compaction system prompt (COMPACTION.md across layers,
        // last wins; built-in default otherwise) and stamp it into the
        // config the agent re-reads each turn.
        const compaction_prompt = try system_prompt.resolveCompaction(
            arena.allocator(),
            self.io,
            self.environ,
            self.agent_dir,
        );
        self.active_config.compaction.compaction_prompt = compaction_prompt;

        self.agent = agent;
        self.rt = rt;
        self.sp_arena = arena;
        self.compaction_prompt = compaction_prompt;
    }

    /// Tear the session down: Lua commands out of the registry, then the
    /// Lua interpreter (extension state, tool source, event bridge), the
    /// prompt arena, and finally the agent — the same relative order the
    /// process teardown always used (runtime dies before agent). Safe on a
    /// never-built or build-failed world.
    fn deinit(self: *SessionWorld) void {
        self.registry.clearLua();
        if (self.rt) |r| r.deinit();
        self.rt = null;
        if (self.sp_arena) |*a| a.deinit();
        self.sp_arena = null;
        self.active_config.compaction.compaction_prompt = null;
        self.compaction_prompt = "";
        if (self.agent) |a| a.deinit();
        self.agent = null;
    }
};

/// The App's session-rebuild hook (/new, /resume): quit-and-relaunch minus
/// the process. Drops all session-scoped UI state, tears down the old world,
/// builds a fresh one through the boot path, and repoints every holder of
/// the old agent/runtime pointers. Commands dispatch only between turns
/// (`tui_app.handleSubmittedLine` is only reached from the idle input pump),
/// so no stream is live across this.
///
/// A mid-rebuild failure leaves no half-dead session: whether it fails
/// before the old world's teardown (`resetSessionUi`) or after,
/// `tui_app.App.rebuildSession` notes the failure in the transcript and
/// surfaces `error.SessionRebuildFailed`, which exits the TUI loop cleanly
/// (process restart is the recovery — no partial rollback).
const RebuildHost = struct {
    world: *SessionWorld,
    app: *tui_app.App,
    cmd_ctx: *command.Context,

    fn rebuild(ctx: *anyopaque, session: panto.Session, conv: ?panto.Conversation) anyerror!void {
        const self: *RebuildHost = @ptrCast(@alignCast(ctx));
        // Transcript entries and bus handlers may reference Lua-bridge
        // memory owned by the outgoing runtime; drop them BEFORE that
        // runtime dies (the mid-run mirror of the boot-time teardown
        // ordering contract, which keeps the bridge alive through the
        // App's teardown).
        try self.app.resetSessionUi();
        self.world.deinit();
        try self.world.build(session, conv);
        try self.wire();
    }

    /// Repoint every borrower of the world's agent/runtime at the CURRENT
    /// world: command Context, Lua event bridge (bus handlers +
    /// override-release hook), selector controller, footer. Called once at
    /// boot (after all borrowers exist) and again after every in-place
    /// rebuild — any new borrower gets wired here, in one place.
    fn wire(self: *RebuildHost) !void {
        const agent = self.world.agent.?;
        self.cmd_ctx.agent = agent;
        self.cmd_ctx.lua_rt = self.world.rt;
        self.cmd_ctx.compaction_prompt = self.world.compaction_prompt;
        if (self.world.rt) |r| {
            try r.eventBridge().attachBus(self.app.eventBus());
            self.app.setOverrideRelease(
                @ptrCast(r.eventBridge()),
                lua_event_bridge.EventBridge.releaseOverrideThunk,
            );
        }
        if (self.app.selectors) |ctrl| {
            ctrl.agent = agent;
            ctrl.resetSessionUsage();
        }
        self.app.footer.setSessionId(agent.sessionId()) catch {};
        self.app.footer.setContextTokens(null);
    }
};

// -----------------------------------------------------------------------------
// Session bootstrap
// -----------------------------------------------------------------------------

/// Mint or resolve the `Session` to drive, against the catalog `store`.
/// Fresh sessions are created on demand; resume resolves by id or picks the
/// most recent. The returned `Session` owns its `info` (freed via the
/// agent's `deinit`, which adopts it).
/// Diagnostics go to stderr: in `-p` print mode stdout is the assistant
/// text a script captures, and stderr is right interactively too.
fn openSession(
    store: panto.SessionStore,
    flags: AgentFlags,
    session_dir: []const u8,
) !panto.Session {
    switch (flags.resume_kind) {
        .none => return store.create(),
        .most_recent => {
            if (try store.latest()) |sess| return sess;
            std.debug.print("no sessions to resume; starting fresh.\n", .{});
            return store.create();
        },
        .by_id => {
            const id = flags.resume_id.?;
            const resolved = store.resolve(id) catch |err| switch (err) {
                error.AmbiguousSessionId => {
                    var buf: [256]u8 = undefined;
                    const stderr = std.debug.lockStderr(&buf);
                    defer std.debug.unlockStderr();
                    const w = &stderr.file_writer.interface;
                    w.writeAll("error: ") catch {};
                    builtin_commands.printAmbiguousSessions(store, id, w) catch {};
                    return error.AmbiguousSessionId;
                },
                else => return err,
            };
            if (resolved) |sess| return sess;
            std.debug.print("error: no session matching '{s}' in {s}\n", .{ id, session_dir });
            return error.SessionNotFound;
        },
    }
}

// -----------------------------------------------------------------------------
// Print mode (-p/--print): one-shot plain-text turn driver
// -----------------------------------------------------------------------------

/// Routes stream events to a writer, printing only assistant Text-block
/// deltas (thinking and tool traffic are dropped) and ensuring the output
/// ends each text block on a newline.
const TextPrinter = struct {
    out: *std.Io.Writer,
    /// Whether the currently open block is a Text block.
    in_text: bool = false,
    last_byte: u8 = '\n',

    fn onEvent(self: *TextPrinter, ev: panto.Event) !void {
        switch (ev) {
            .block_start => |bs| self.in_text = bs.block_type == .Text,
            .content_delta => |cd| {
                if (self.in_text) {
                    try self.out.writeAll(cd.delta);
                    if (cd.delta.len > 0) self.last_byte = cd.delta[cd.delta.len - 1];
                }
            },
            .block_complete => {
                if (self.in_text and self.last_byte != '\n') {
                    try self.out.writeAll("\n");
                    self.last_byte = '\n';
                }
                self.in_text = false;
            },
            else => {},
        }
    }
};

/// Drive one agent turn without the TUI: assistant text to `stdout`, errors
/// to the caller. Mirrors `tui_app.driveTurnBlocks`' two one-shot fallbacks
/// (adaptive-thinking rewrite, forced auth refresh). Persistence rides on the
/// agent exactly as in TUI mode.
fn runPrintTurn(
    alloc: std.mem.Allocator,
    agent: *panto.Agent,
    active_config: *panto.Config,
    provider_name: []const u8,
    auth_mgr: *auth_manager.AuthManager,
    stdout_file: *std.Io.File.Writer,
    prompt: []const u8,
) !void {
    const stdout = &stdout_file.interface;
    // No presenter: an unauthenticated oauth provider fails with
    // LoginRequired rather than starting an interactive device login.
    try auth_mgr.resolveInto(active_config, provider_name, false, null);
    agent.setConfig(active_config);

    var blocks = [_]panto.ContentBlock{
        .{ .Text = try panto.textualBlockFromSlice(alloc, prompt) },
    };
    var stream = try agent.run(.{ .blocks = &blocks });
    defer stream.deinit();

    var printer: TextPrinter = .{ .out = stdout };
    var fallback_used = false;
    var auth_retry_used = false;
    while (true) {
        const ev = stream.next() catch |err| {
            if (!fallback_used and err == error.ProviderBadRequest and
                tui_selectors.adaptiveFallback(&active_config.provider))
            {
                fallback_used = true;
                agent.setConfig(active_config);
                try stream.reopen();
                continue;
            }
            if (!auth_retry_used and err == error.ProviderAuthFailed) {
                auth_retry_used = true;
                auth_mgr.resolveInto(active_config, provider_name, true, null) catch return err;
                agent.setConfig(active_config);
                try stream.reopen();
                continue;
            }
            return err;
        };
        const e = ev orelse break;
        try printer.onEvent(e);
        try stdout_file.flush(); // stream text as it arrives
    }
    try stdout_file.flush();
}

test "TextPrinter prints only Text deltas, newline-terminated" {
    var out = std.Io.Writer.Allocating.init(std.testing.allocator);
    defer out.deinit();
    var p: TextPrinter = .{ .out = &out.writer };

    try p.onEvent(.{ .message_start = .assistant });
    try p.onEvent(.{ .block_start = .{ .block_type = .Thinking, .index = 0 } });
    try p.onEvent(.{ .content_delta = .{ .index = 0, .delta = "pondering" } });
    try p.onEvent(.{ .block_start = .{ .block_type = .Text, .index = 1 } });
    try p.onEvent(.{ .content_delta = .{ .index = 1, .delta = "hello" } });
    try p.onEvent(.{ .content_delta = .{ .index = 1, .delta = " world" } });
    try p.onEvent(.{ .block_complete = .{ .index = 1, .block = undefined } });
    try p.onEvent(.turn_complete);
    try std.testing.expectEqualStrings("hello world\n", out.written());
}