Agent Guide for Telegram Desktop

This guide defines repository-wide instructions for coding agents working with the Telegram Desktop codebase.

Working from Codex on Windows + WSL

This checkout may be opened in Codex Desktop through the Windows UNC path \\wsl.localhost\{distro}\home\{user}\Telegram\tdesktop, while the real Linux path is /home/{user}/Telegram/tdesktop. Treat it as a WSL/Linux checkout first, not as a native Windows checkout.

Prefer running repository-aware commands through WSL:

wsl.exe -d {distro} --cd /home/{user}/Telegram/tdesktop -- <command>

PowerShell can read and write files through the UNC path, but native Windows tools may see different ownership, path, executable, or line-ending behavior than Linux tools.
Git from PowerShell over \\wsl.localhost\... can fail with detected dubious ownership. Use WSL Git instead. Do not change global Git safe.directory settings unless the user explicitly asks for that.
Keep path styles matched to the shell. Use /home/{user}/Telegram/tdesktop/... with WSL commands, and quoted \\wsl.localhost\{distro}\home\{user}\Telegram\tdesktop\... paths with native Windows commands. Avoid passing UNC paths to Linux tools or Linux paths to native Windows tools unless the tool explicitly supports them.
If a command behaves strangely from the PowerShell UNC working directory, retry the same command through wsl.exe -d {distro} --cd /home/{user}/Telegram/tdesktop -- ... before concluding the repository or command is broken.
Recursive searches and repo inspection are usually faster and more faithful through WSL, for example wsl.exe -d {distro} --cd /home/{user}/Telegram/tdesktop -- rg ....
Existing build outputs may be Linux binaries, for example out/Debug/Telegram as an ELF executable, not Telegram.exe. Verify the build tree before assuming which platform produced it.
Be careful with text file line endings. In a WSL/Linux checkout, files should remain LF-only unless the file already uses another convention. CRLF finishing applies only to native, non-WSL Windows runs/checkouts. Do not let PowerShell or Windows tools silently rewrite WSL files to CRLF. If a file becomes mixed, normalize it back to the convention appropriate for the current checkout, without adding a UTF-8 BOM.
When using the local perform-task skill from this WSL checkout, keep external AI task artifacts and edited project text files LF-only. Treat its Windows text-normalization phase as not applicable to WSL, except to record that line endings were checked and kept LF/no-BOM. Run CRLF normalization only in a native, non-WSL Windows checkout.

Build System Structure

The build system expects this directory layout:

L:\Telegram\                    # BuildPath
L:\Telegram\tdesktop\           # Repository (you work here)
L:\Telegram\Libraries\          # 32-bit dependencies (Linux/macOS)
L:\Telegram\win64\Libraries\    # 64-bit dependencies (Windows)
L:\Telegram\ThirdParty\         # Build tools (NuGet, Python, etc.)

Dependencies are located relative to the repository: ../Libraries, ../win64/Libraries, or ../ThirdParty.

Build Configuration

Build Commands

From repository root, run:

cmake --build out --config Debug --target Telegram

That's it. The out/ directory is already configured. The executable will be at out/Debug/Telegram.exe.

On Linux, build and test with:

source .env && bash ./scripts/build_debug.sh

The build requires API_ID and API_HASH. Before invoking the script, attempt to inject them with source .env; export them directly if .env is unavailable. Do not run this build script in a sandboxed environment.

Important: When running cmake from a shell that doesn't support cd, use quoted absolute paths:

cmake --build "l:\Telegram\tx64\out" --config Debug --target Telegram

Never build Release - it's extremely heavy and not needed for testing changes.

Platform-Specific Requirements

Windows

Requires Visual Studio 2022
Must run from appropriate Native Tools Command Prompt:
- "x64 Native Tools Command Prompt" for win64
- "x86 Native Tools Command Prompt" for win
- "ARM64 Native Tools Command Prompt" for winarm
Dependencies: ../win64/Libraries (64-bit) or ../Libraries (32-bit)

macOS

Requires Xcode
Dependencies: ../Libraries/local/Qt-*
First-time configure of a new out/ tree: set the QT environment variable to the Qt version this checkout actually has, for example export QT=6.11.1 when ../Libraries/local/Qt-6.11.1 is the installed one. The value names a directory, so it is the checkout's version, not a constant.
Reconfiguring an existing out/ tree: do not export QT. Run env -u QT cmake -S . -B out instead. cmake/external/qt/package.cmake writes an exported QT into the qt_requested cache entry with FORCE, so it overwrites the version the tree was already configured with instead of being ignored. A value that disagrees with the configured tree then fails the regeneration, and the generated project keeps the source list it was last generated with: newly added sources are never compiled — which surfaces later as undefined-symbol link errors rather than as a configure error — and newly added .style modules leave the generated style_*.h includes stale.

Linux

Build dependencies in ../Libraries
Set QT environment variable if needed
Use source .env && bash ./scripts/build_debug.sh for build and test; run it outside the sandbox.

Key Files

Telegram/build/version - Version information
out/ - Build output directory

Troubleshooting

"Libraries not found"

Ensure the repository is in L:\Telegram\tdesktop. The build system requires ../win64/Libraries to exist.

Build fails with "wrong command prompt"

On Windows, use the correct Visual Studio Native Tools Command Prompt matching your target (x64/x86/ARM64).

macOS crashes while reading the cached language pack

After an incremental Xcode build that regenerated lang.strings outputs, the app can link a new generated key lookup with stale objects that still use an older kKeysCount. The characteristic failure is:

the Debug log stops immediately after Lang Info: Loaded cached, keys: ...;
stderr and tdata/working may be empty;
a fresh ~/Library/Logs/DiagnosticReports/Telegram-*.ips shows SIGABRT from std::vector<unsigned char>::operator[], then Lang::Instance::applyValue(), fillFromSerialized(), and Local::readLangPack().

If this exact startup failure repeats twice, do not change the implementation, test overlay, or portable account. Stop only this checkout's exact Telegram process. Because Xcode's CONFIGURATION_BUILD_DIR is out/Debug, make a safety copy of every existing portable folder outside out/ before cleaning:

portable_backup_root="$(mktemp -d "${TMPDIR:-/tmp}/tdesktop-portable-clean.XXXXXX")"
for portable_name in \
  TelegramForcePortable \
  test_TelegramForcePortable \
  real_TelegramForcePortable; do
  if [ -d "out/Debug/$portable_name" ]; then
    ditto "out/Debug/$portable_name" "$portable_backup_root/$portable_name"
  fi
done

Require every expected backup copy to exist before continuing. Then perform one full Xcode Debug clean and rebuild:

cmake --build out --config Debug --target clean
cmake --build out --config Debug --target Telegram

Afterward, restore a portable folder from the backup only when its original path is missing; never overwrite a folder that survived the clean. Verify all three original folder names that existed before the clean are present, keep the backup until the rebuilt app completes one successful launch, and record its path if the run stops before verification. Then rerun the same test once. If the signature persists after that clean rebuild, continue normal crash diagnosis or report the blocker. Do not loop clean rebuilds.

Build output locks

For builds owned by the autonomous continue / perform-task workflow, read and follow .agents/shared/build-lock-recovery.md. PDB, EXE, OBJ, and other build-output lock errors are recoverable: stop only the exact checkout executable or verified build-tree holders, delete only exact named artifacts inside that checkout's build tree, and retry within the bounded recovery budget. Never stop an installed Telegram client, another checkout, an IDE, or an unknown process.

Outside that autonomous workflow, an exact checkout executable may be running because the user is testing it. Do not terminate it or delete locked build outputs without explicit permission. Report the exact locked path and ask the user to close that checkout's Telegram/debugger before rebuilding.

Best Practices

Always use Debug builds - Release builds are extremely heavy
Don't build Release configuration - it's too heavy for testing

Debug-Only Code

Production translation units stay free of debug machinery. The permanent test harness lives in Telegram/SourceFiles/test/, and the disposable -testagent overlay owns per-task instrumentation; production code carries at most a thin single-call seam (a Test::Fire()-style waitpoint or a live-object publication at a construction seam).

Do not add #ifdef _DEBUG blocks, debug-only types, debug state, mutexes, counters, or observation structs to production headers or sources. When a behavior cannot be observed without such machinery, that is a harness gap: extend the test/ helpers or the overlay instead.
Never commit debugging machinery interleaved with working code in the same translation unit. A permanent helper belongs under test/; a temporary one belongs in the overlay and is never retained.
Exceptions exist — a few #ifdef _DEBUG hooks are deliberately kept in production files — but they are exceptions and each new one needs a solid, stated reason. "The test needed it" is not one.

Text File Format

On Windows, keep project text files with CRLF line endings.
Do not save source, header, build/config, style, or localization files as UTF-8 with BOM. Use UTF-8 without BOM.
When rewriting project text files for normalization, preserve file content otherwise and do not introduce a BOM.

Commits

Subject: one concise, plain-language line summarizing the change, ~50-60 characters, matching the style of recent git log subjects. This is usually the entire message.
Decide the [ai] prefix separately for each commit. Use it only when every retained change in that commit, and the commit's purpose, are exclusively about the AI workflow: the agent harness, skills, prompts, custom commands, agent documentation, or AI testing infrastructure. Typical qualifying paths include Telegram/SourceFiles/test/, .agents/, .claude/, .grok/, AGENTS.md, CLAUDE.md, and GROK.md, but paths alone do not decide the prefix. Product-specific test seams, app code, and build-system integration do not qualify merely because agents use them for verification. Split mixed workflow and product work into separate commits when practical; otherwise the mixed commit must not use [ai] . Do not count the disposable test overlay or external AI task artifacts. Every other commit must not contain [ai] anywhere.
The [ai] prefix marks the commit's scope, never its authorship. It does not mean "authored by an AI": an AI-authored product fix takes a plain subject, and a workflow-only commit takes the prefix no matter who wrote it.
For ordinary work not associated with an AI task, add a short plain-language body only when the subject can't carry it (what was done, not the technical how) — a line or two at most.
Never add a Co-Authored-By: line or any tool/assistant attribution trailer.
Never add Autotask:/attempt or other internal run markers. A commit owned by an ai-tdesktop task has exactly three lines: the concise subject, a blank line, and Task: <task-id>. Do not add a body. Keep rationale and implementation notes out of the commit message; put a short durable note under tasks/<task-id>.md only when useful. Do not copy commit hashes into that note or any AI task artifact; the task id is the cross-repository link.

Local Storage Serialization

Both app-level (Core::Settings) and session-level (Main::SessionSettings) use sequential binary serialization via QDataStream. Key rules:

New fields must ALWAYS be appended at the end of the stream, never inserted in the middle
Reading new fields must be guarded with !stream.atEnd() and provide a meaningful default/fallback
Inserting in the middle breaks reading of data saved by older versions (the new read code consumes bytes that belong to subsequent fields)
For simple flags and values, prefer using the generic KV prefs facility (writePref<Type> / readPref<Type>) instead of adding to the binary stream -- this avoids serialization ordering issues entirely

Development Guidelines

Coding Style

Do NOT write useless comments in code:

This is important! Do not write single-line comments that describe what the next line does - they are bloat. Comments are allowed ONLY to describe complex algorithms in detail, when the explanation requires at least 4-5 lines. Self-documenting code with clear variable and function names is preferred.

Do not remove existing comments just to satisfy this rule. Preserve comments unless your change makes them incorrect or truly obsolete; when moving or refactoring code, move the useful comment with it. Inline comments that label positional arguments for generated or schema-driven APIs (for example TL/MTP constructors) are useful because the field names are not visible in the call itself.

// BAD - don't do this:
// Get the user's name
auto name = user->name();
// Check if premium
if (user->isPremium()) {

// GOOD - no comments needed, code is self-explanatory:
auto name = user->name();
if (user->isPremium()) {

// ACCEPTABLE - complex algorithm explanation (4+ lines):
// The algorithm works by first collecting all visible messages
// in the viewport, then calculating their intersection with
// the clip rectangle. Messages are grouped by date headers,
// and we need to account for sticky headers that may overlap
// with the first message in each group.

Style and formatting rules are in REVIEW.md — see that file for empty-line-before-closing-brace, operator placement in multi-line expressions, if-with-initializer, and other mechanical style rules.

Never discard a result with a cast: static_cast<void>(...) and (void)expr are banned; instead of silencing [[nodiscard]], fix the design.

Use auto for type deduction:

Prefer auto (or const auto, const auto &) instead of explicit types:

// Prefer this:
auto currentTitle = tr::lng_settings_title(tr::now);
auto nameProducer = GetNameProducer();

// Instead of this:
QString currentTitle = tr::lng_settings_title(tr::now);
rpl::producer<QString> nameProducer = GetNameProducer();

Use trailing return types only when the normal form is too long:

Prefer the normal return type form when the opening line fits comfortably, roughly around 77 characters or less:

// GOOD:
[[nodiscard]] TextWithEntities FlattenSummaryBlocks(
	const std::vector<Block> &blocks);

Do not use one-line trailing return types, or put the trailing return type after ) on the same line. If it fits on one line with trailing syntax, the normal form would be shorter and easier to read:

// BAD:
auto ComputeTitle() -> QString;

// BAD:
[[nodiscard]] auto FlattenSummaryBlocks(
	const std::vector<Block> &blocks) -> TextWithEntities;

Use auto with a trailing return type only when the normal opening line {attributes} {return-type} {class-name::}{function-name(} would be too long, or would force the return type onto its own line. Put the arrow and return type on the next line so the return type remains easy to find:

// BAD:
not_null<HistoryView::Controls::ComposeAiButton*>
HistoryView::Controls::SetupCaptionAiButton(SetupCaptionAiButtonArgs &&args);

// GOOD:
auto HistoryView::Controls::SetupCaptionAiButton(
		SetupCaptionAiButtonArgs &&args)
-> not_null<HistoryView::Controls::ComposeAiButton*>;

This applies to both declarations and definitions.

Use _q for QString literals:

Prefer the project literal u"..."_q instead of the verbose QStringLiteral("...") macro when creating QString values:

// Prefer this:
auto text = u"Settings"_q;

// Instead of this:
auto text = QStringLiteral("Settings");

Never use Q_OS_LINUX for platform checks in new code:

Telegram Desktop distinguishes at most three platforms: Windows / macOS / all-other. The "all-other" branch covers Linux, the BSD variants and more — and this is almost always the branch you want. Q_OS_LINUX narrows it to Linux alone, silently excluding the non-Linux Unix platforms, which is almost never intended. For the all-other branch use !defined Q_OS_WIN && !defined Q_OS_MAC at compile time, or its runtime equivalent Platform::IsLinux() — which, despite the name, means exactly !defined Q_OS_WIN && !defined Q_OS_MAC ("everything except Windows and macOS"), not Linux specifically:

// BAD - excludes FreeBSD and other non-Linux Unix:
#ifdef Q_OS_LINUX
UnixSpecificCode();
#endif // Q_OS_LINUX

// GOOD - the all-other branch, compile time:
#if !defined Q_OS_WIN && !defined Q_OS_MAC
UnixSpecificCode();
#endif // !Q_OS_WIN && !Q_OS_MAC

// GOOD - the all-other branch, runtime (same meaning, NOT Linux-only):
if (Platform::IsLinux()) {
	UnixSpecificCode();
}

Q_OS_LINUX is only for the rare case where you genuinely want exactly Linux and not the other Unix-like systems — usually you don't. The few existing uses (Telegram/SourceFiles/core/sandbox.cpp, Telegram/SourceFiles/platform/linux/specific_linux.cpp) are such genuinely Linux-only code paths and stay as-is.

Treat CMake LINUX as the all-other platform:

In this project, cmake/validate_special_target.cmake sets LINUX in the final else() after checking WIN32 and APPLE. It therefore means NOT WIN32 AND NOT APPLE, including non-Linux Unix platforms; it does not mean exactly Linux. For the usual three-way platform split, write:

if (WIN32)
    set(platform_source platform/win.cpp)
elseif (APPLE)
    set(platform_source platform/mac.mm)
else()
    set(platform_source platform/linux.cpp)
endif()
target_sources(my_target PRIVATE ${platform_source})

Do not add a separate fallback branch after if (LINUX) as though LINUX were one platform among several remaining platforms. There are no remaining platforms in this project's CMake platform model.

Prefer cppgir wrappers over the GLib C API:

When implementing all-other-platform code with GLib, GObject, or GIO, use the generated cppgir C++ bindings under gi::repository as much as possible. Prefer their GLib, GObject, and Gio types, ownership handling, results, and callbacks over raw g_*, g_object_*, and g_io_* APIs. Use the C API only when cppgir does not expose the required functionality or at a narrow interop boundary that genuinely requires raw GLib types, and keep that raw API surface as small as possible.

Generate typed D-Bus bindings from introspection XML:

For a D-Bus interface known at build time, prefer the CMake generate_dbus function from cmake/external/glib/generate_dbus.cmake over handwritten GDBusProxy calls, stringly typed method and signal names, or manually maintained C wrappers. Its signature is:

generate_dbus(
    target_name
    interface_prefix
    namespace
    interface_file)

target_name is the existing target that will use the bindings, interface_prefix is the common D-Bus interface prefix passed to gdbus-codegen, namespace names the generated API, and interface_file is the D-Bus introspection XML file. Include the helper and call it inside the all-other-platform branch:

include(${cmake_helpers_loc}/external/glib/generate_dbus.cmake)
generate_dbus(
    my_target
    org.example.
    Example
    ${src_loc}/platform/linux/org.example.Service.xml)

The helper runs gdbus-codegen, generates proxy, skeleton, and object-manager types, produces GIR metadata, wraps that metadata with cppgir, and links the result into target_name. Consume the resulting typed API from gi::repository::Example (using the namespace argument from the example); do not edit or separately list files under the build gen directory. Use generic GLib D-Bus calls only when the interface is genuinely dynamic or cannot be represented by suitable introspection XML.

API Usage

API Schema Files

API definitions use TL Language:

Telegram/SourceFiles/mtproto/scheme/mtproto.tl - MTProto protocol (encryption, auth, etc.)
Telegram/SourceFiles/mtproto/scheme/api.tl - Telegram API (messages, users, chats, etc.)

Making API Requests

Standard pattern using api(), generated MTP... types, and callbacks:

api().request(MTPnamespace_MethodName(
    MTP_flags(flags_value),
    MTP_inputPeer(peer),
    MTP_string(messageText),
    MTP_long(randomId),
    MTP_vector<MTPMessageEntity>()
)).done([=](const MTPResponseType &result) {
    // Handle successful response

    // Multiple constructors - use .match() or check type:
    result.match([&](const MTPDuser &data) {
        // use data.vfirst_name().v
    }, [&](const MTPDuserEmpty &data) {
        // handle empty user
    });

    // Single constructor - use .data() shortcut:
    const auto &data = result.data();
    // use data.vmessages().v

}).fail([=](const MTP::Error &error) {
    // Handle API error
    if (error.type() == u"FLOOD_WAIT_X"_q) {
        // Handle flood wait
    }
}).handleFloodErrors().send();

Key points:

Always refer to api.tl for method signatures and return types
Use generated MTP... types for parameters (MTP_int, MTP_string, etc.)

For multiple constructors, use .match() or check .type() against mtpc_ constants then call .c_constructorName():

// Using match:
result.match([&](const MTPDuser &data) { ... }, [&](const MTPDuserEmpty &data) { ... });
// Or explicit type check:
if (result.type() == mtpc_user) {
    const auto &data = result.c_user(); // asserts on type mismatch
}

For single constructors, use .data() shortcut
Include .handleFloodErrors() before .send() in rare cases where you want special case flood error handling
Silently ignore HTTP 406 errors in UI: the server uses 406 to mean "show nothing to the user". Guard toasts with MTP::IgnoreError(error) or use MTP::ShowErrorFallback(show, error) (both in mtproto/mtproto_response.h) which shows error.type() as a toast unless the error should be ignored.

API Request Callback Lifetime

api().request(...) callbacks are owned by the session, not by whatever created them. A .done() / .fail() handler stays alive for the whole session lifetime, so a handler that captured a widget, a box, a controller, or any shorter-lived state still runs after that state is gone. A plain [=] capture warns about nothing, which makes this one of the easiest ways to write a use-after-free here.

Capturing only plain values or session-owned objects is fine. When anything captured can die before the session does, pick one of three:

1. Guard the callback with crl::guard. The request is always sent; the handler is skipped when the context is gone. Use when the call itself must reach the server and only the local reaction is optional.

api().request(MTPmethod(
	...
)).done(crl::guard(this, [=](const MTPResult &result) {
	// runs only while `this` is still alive
})).send();

Accepted guards, in rough order of how often they are used: a raw pointer or not_null to any QObject-derived type — widgets, boxes, controllers — where the QPointer is created on the spot, so passing this is the normal case; a raw pointer or not_null to a base::has_weak_ptr type; QPointer, QWeakPointer, QSharedPointer; base::weak_ptr, base::weak_qptr; std::weak_ptr, std::shared_ptr; and base::binary_guard.

2. Remember the mtpRequestId and cancel it. Cancel when the result stops being relevant, and in the destructor. The request may never reach the server — if it is still queued when cancelled, or connectivity dies first, it is simply dropped — so never use this when the call itself has to happen.

_requestId = api().request(MTPmethod(
	...
)).done([=](const MTPResult &result) {
	_requestId = 0;
	...
}).send();

// when the result is no longer relevant, and in the destructor:
api().request(base::take(_requestId)).cancel();

3. Own an MTP::Sender. Its destructor cancels everything it sent that is still in flight, so request lifetime follows the owner with no bookkeeping. Same delivery caveat as (2). Prefer this for a widget, box, or controller that issues more than a request or two.

// header
	MTP::Sender _api;

// constructor initializer list
, _api(&session->mtp())

// requests sent through it die with the owner
_api.request(MTPmethod(
	...
)).done([=](const MTPResult &result) {
	...
}).send();

Choosing between them: if the server must see the request, use (1). If it only matters while its owner is alive, use (3) — or (2) when a single request does not justify a Sender member.

UI Styling

Style Files

UI styles are defined in .style files using custom syntax:

using "ui/basic.style";
using "ui/widgets/widgets.style";

MyButtonStyle {
    textPadding: margins;
    icon: icon;
    height: pixels;
}

defaultButton: MyButtonStyle {
    textPadding: margins(10px, 15px, 10px, 15px);
    icon: icon{{ "gui/icons/search", iconColor }};
    height: 30px;
}

primaryButton: MyButtonStyle(defaultButton) {
    icon: icon{{ "gui/icons/check", iconColor }};
}

Built-in types:

int - Integer numbers (e.g., maxLines: 3;)
bool - Boolean values (e.g., useShadow: true;)
pixels - Pixel values with px suffix (e.g., 10px)
color - Named colors from ui/colors.palette
icon - Inline icon definition: icon{{ "path/stem", color }}
margins - Four values: margins(left, top, right, bottom)
size - Two values: size(width, height)
point - Two values: point(x, y)
align - Alignment: align(center), align(left)
font - Font: font(14px semibold)
double - Floating point

Multi-part icons (layers drawn bottom-up):

myComplexIcon: icon{
  { "gui/icons/background", iconBgColor },
  { "gui/icons/foreground", iconFgColor }
};

Borders are typically separate fields, not a single property:

chatInput {
  border: 1px;                       // width
  borderFg: defaultInputFieldBorder; // color
}

Never hardcode sizes in code:

The app supports different interface scale options. Style px values are automatically scaled at runtime, but raw integer constants in code are not. Never use hardcoded numbers for margins, paddings, spacing, sizes, coordinates, or any other dimensional values. Always define them in .style files and reference via st::.

// BAD - breaks at non-100% interface scale:
p.drawText(10, 20, text);
widget->setFixedHeight(48);
auto margin = 8;
auto iconSize = QSize(24, 24);

// GOOD - define in .style file and reference:
p.drawText(st::myWidgetTextLeft, st::myWidgetTextTop, text);
widget->setFixedHeight(st::myWidgetHeight);
auto margin = st::myWidgetMargin;
auto iconSize = st::myWidgetIconSize;

Duration constants: Animation durations should NOT go in .style files, this is a legacy approach. Prefer constexpr auto kName = crl::time(N) in an anonymous namespace in the relevant .cpp file.

Usage in Code

#include "styles/style_widgets.h"

// Access style members
int height = st::primaryButton.height;
const style::icon &icon = st::primaryButton.icon;
style::margins padding = st::primaryButton.textPadding;

// Use in painting
void MyWidget::paintEvent(QPaintEvent *e) {
    Painter p(this);
    p.fillRect(rect(), st::chatInput.backgroundColor);
}

Localization

String Definitions

Strings are defined in Telegram/Resources/langs/lang.strings:

"lng_settings_title" = "Settings";
"lng_confirm_delete_item" = "Are you sure you want to delete {item_name}?";
"lng_files_selected#one" = "{count} file selected";
"lng_files_selected#other" = "{count} files selected";

Usage in Code

Immediate (current value):

auto currentTitle = tr::lng_settings_title(tr::now);

auto currentConfirmation = tr::lng_confirm_delete_item(
    tr::now,
    lt_item_name, currentItemName);

auto filesText = tr::lng_files_selected(tr::now, lt_count, count);

Reactive (rpl::producer):

auto titleProducer = tr::lng_settings_title();

auto confirmationProducer = tr::lng_confirm_delete_item(
    lt_item_name,
    std::move(itemNameProducer));

auto filesTextProducer = tr::lng_files_selected(
    lt_count,
    countProducer | tr::to_count());

Key points:

Pass tr::now as first argument for immediate QString
Omit tr::now for reactive rpl::producer<QString>
Placeholders use lt_tag_name, value pattern
For {count}: immediate uses int, reactive uses rpl::producer<float64> with | tr::to_count()
Move producers with std::move when passing to placeholders
Rich text projectors — these tr:: helpers serve double duty: as the last argument (projector) they set the return type to TextWithEntities, and as placeholder values they wrap individual substitutions in formatting. Always prefer them over Ui::Text::Bold(), Ui::Text::RichLangValue, etc. — see REVIEW.md for the full mapping.
- tr::marked — basic projection, converts QString to TextWithEntities
- tr::rich — interprets **bold**/__italic__ markup in the string
- tr::bold, tr::italic, tr::underline — wrap text in that formatting
- tr::link — wrap as a clickable link
- tr::url(u"https://..."_q) — returns a projection that converts text to a link pointing to the given URL; can be passed to rpl::map or directly to a tr::lng_... call
```
// As last argument (projector):
auto title = tr::lng_export_progress_title(tr::now, tr::bold);
auto text = tr::lng_proxy_incorrect_secret(tr::now, tr::rich);
// As placeholder value wrapper + projector:
auto desc = tr::lng_some_key(
    tr::now,
    lt_name,
    tr::bold(userName),
    lt_group,
    tr::bold(groupName),
    tr::rich);
// Nested tr::lng as placeholder:
auto linked = tr::lng_settings_birthday_contacts(
    lt_link,
    tr::lng_settings_birthday_contacts_link(tr::url(link)),
    tr::marked);
```

RPL (Reactive Programming Library)

Core Concepts

Producers represent streams of values over time:

auto intProducer = rpl::single(123);  // Emits single value
auto lifetime = rpl::lifetime();       // Manages subscription lifetime

Starting Pipelines

std::move(counter) | rpl::on_next([=](int value) {
    qDebug() << "Received: " << value;
}, lifetime);

// Without lifetime parameter - MUST store returned lifetime:
auto subscriptionLifetime = std::move(counter) | rpl::on_next([=](int value) {
    // process value
});

Transforming Producers

auto strings = std::move(ints) | rpl::map([](int value) {
    return QString::number(value * 2);
});

auto evenInts = std::move(ints) | rpl::filter([](int value) {
    return (value % 2 == 0);
});

Combining Producers

rpl::combine - combines latest values (lambdas receive unpacked arguments):

auto combined = rpl::combine(countProducer, textProducer);

std::move(combined) | rpl::on_next([=](int count, const QString &text) {
    qDebug() << "Count=" << count << ", Text=" << text;
}, lifetime);

rpl::merge - merges producers of same type:

auto merged = rpl::merge(sourceA, sourceB);

std::move(merged) | rpl::on_next([=](QString &&value) {
    qDebug() << "Merged value: " << value;
}, lifetime);

Other pipeline starters — besides rpl::on_next, there are:

rpl::on_error([=](Error &&e) { ... }, lifetime) — handle errors
rpl::on_done([=] { ... }, lifetime) — handle stream completion
rpl::on_next_error_done(nextCb, errorCb, doneCb, lifetime) — handle all three

The Error template parameter defaults to rpl::no_error: rpl::producer<Type, Error = no_error>.

Key points:

Explicitly std::move producers when starting pipelines
Pass rpl::lifetime to on_... methods or store returned lifetime
Use rpl::duplicate(producer) to reuse a producer multiple times
Combined producers automatically unpack tuples in lambdas (works with rpl::map, rpl::filter, and rpl::on_next)

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Agent Guide for Telegram Desktop

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Build System Structure

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Build Commands

Platform-Specific Requirements

Windows

macOS

Linux

Key Files

Troubleshooting

"Libraries not found"

Build fails with "wrong command prompt"

macOS crashes while reading the cached language pack

Build output locks

Best Practices

Debug-Only Code

Text File Format

Commits

Local Storage Serialization

Development Guidelines

Coding Style

API Usage

API Schema Files

Making API Requests

API Request Callback Lifetime

UI Styling

Style Files

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RPL (Reactive Programming Library)

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AGENTS.md

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AGENTS.md

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Agent Guide for Telegram Desktop

Working from Codex on Windows + WSL

Build System Structure

Build Configuration

Build Commands

Platform-Specific Requirements

Windows

macOS

Linux

Key Files

Troubleshooting

"Libraries not found"

Build fails with "wrong command prompt"

macOS crashes while reading the cached language pack

Build output locks

Best Practices

Debug-Only Code

Text File Format

Commits

Local Storage Serialization

Development Guidelines

Coding Style

API Usage

API Schema Files

Making API Requests

API Request Callback Lifetime

UI Styling

Style Files

Usage in Code

Localization

String Definitions

Usage in Code

RPL (Reactive Programming Library)

Core Concepts

Starting Pipelines

Transforming Producers

Combining Producers