# Project architecture @architecture.md # Project conventions @project-conventions.md ## usage_rules usage _A config-driven dev tool for Elixir projects to manage AGENTS.md files and agent skills from dependencies_ ## Using Usage Rules Many packages have usage rules, which you should *thoroughly* consult before taking any action. These usage rules contain guidelines and rules *directly from the package authors*. They are your best source of knowledge for making decisions. ## Modules & functions in the current app and dependencies When looking for docs for modules & functions that are dependencies of the current project, or for Elixir itself, use `mix usage_rules.docs` ``` # Search a whole module mix usage_rules.docs Enum # Search a specific function mix usage_rules.docs Enum.zip # Search a specific function & arity mix usage_rules.docs Enum.zip/1 ``` ## Searching Documentation You should also consult the documentation of any tools you are using, early and often. The best way to accomplish this is to use the `usage_rules.search_docs` mix task. Once you have found what you are looking for, use the links in the search results to get more detail. For example: ``` # Search docs for all packages in the current application, including Elixir mix usage_rules.search_docs Enum.zip # Search docs for specific packages mix usage_rules.search_docs Req.get -p req # Search docs for multi-word queries mix usage_rules.search_docs "making requests" -p req # Search only in titles (useful for finding specific functions/modules) mix usage_rules.search_docs "Enum.zip" --query-by title ``` ## usage_rules:elixir usage # Elixir Core Usage Rules ## Pattern Matching - Use pattern matching over conditional logic when possible - Prefer to match on function heads instead of using `if`/`else` or `case` in function bodies - `%{}` matches ANY map, not just empty maps. Use `map_size(map) == 0` guard to check for truly empty maps ## Error Handling - Use `{:ok, result}` and `{:error, reason}` tuples for operations that can fail - Avoid raising exceptions for control flow - Use `with` for chaining operations that return `{:ok, _}` or `{:error, _}` ## Common Mistakes to Avoid - Elixir has no `return` statement, nor early returns. The last expression in a block is always returned. - Don't use `Enum` functions on large collections when `Stream` is more appropriate - Avoid nested `case` statements - refactor to a single `case`, `with` or separate functions - Don't use `String.to_atom/1` on user input (memory leak risk) - Lists and enumerables cannot be indexed with brackets. Use pattern matching or `Enum` functions - Prefer `Enum` functions like `Enum.reduce` over recursion - When recursion is necessary, prefer to use pattern matching in function heads for base case detection - Using the process dictionary is typically a sign of unidiomatic code - Only use macros if explicitly requested - There are many useful standard library functions, prefer to use them where possible ## Function Design - Use guard clauses: `when is_binary(name) and byte_size(name) > 0` - Prefer multiple function clauses over complex conditional logic - Name functions descriptively: `calculate_total_price/2` not `calc/2` - Predicate function names should not start with `is` and should end in a question mark. - Names like `is_thing` should be reserved for guards ## Data Structures - Use structs over maps when the shape is known: `defstruct [:name, :age]` - Prefer keyword lists for options: `[timeout: 5000, retries: 3]` - Use maps for dynamic key-value data - Prefer to prepend to lists `[new | list]` not `list ++ [new]` ## Mix Tasks - Use `mix help` to list available mix tasks - Use `mix help task_name` to get docs for an individual task - Read the docs and options fully before using tasks ## Testing - Run tests in a specific file with `mix test test/my_test.exs` and a specific test with the line number `mix test path/to/test.exs:123` - Limit the number of failed tests with `mix test --max-failures n` - Use `@tag` to tag specific tests, and `mix test --only tag` to run only those tests - Use `assert_raise` for testing expected exceptions: `assert_raise ArgumentError, fn -> invalid_function() end` - Use `mix help test` to for full documentation on running tests ## Debugging - Use `dbg/1` to print values while debugging. This will display the formatted value and other relevant information in the console. ## usage_rules usage _A config-driven dev tool for Elixir projects to manage AGENTS.md files and agent skills from dependencies_ ## Using Usage Rules Many packages have usage rules, which you should *thoroughly* consult before taking any action. These usage rules contain guidelines and rules *directly from the package authors*. They are your best source of knowledge for making decisions. ## Modules & functions in the current app and dependencies When looking for docs for modules & functions that are dependencies of the current project, or for Elixir itself, use `mix usage_rules.docs` ``` # Search a whole module mix usage_rules.docs Enum # Search a specific function mix usage_rules.docs Enum.zip # Search a specific function & arity mix usage_rules.docs Enum.zip/1 ``` ## Searching Documentation You should also consult the documentation of any tools you are using, early and often. The best way to accomplish this is to use the `usage_rules.search_docs` mix task. Once you have found what you are looking for, use the links in the search results to get more detail. For example: ``` # Search docs for all packages in the current application, including Elixir mix usage_rules.search_docs Enum.zip # Search docs for specific packages mix usage_rules.search_docs Req.get -p req # Search docs for multi-word queries mix usage_rules.search_docs "making requests" -p req # Search only in titles (useful for finding specific functions/modules) mix usage_rules.search_docs "Enum.zip" --query-by title ``` ## usage_rules:otp usage # OTP Usage Rules ## GenServer Best Practices - Keep state simple and serializable - Handle all expected messages explicitly - Use `handle_continue/2` for post-init work - Implement proper cleanup in `terminate/2` when necessary ## Process Communication - Use `GenServer.call/3` for synchronous requests expecting replies - Use `GenServer.cast/2` for fire-and-forget messages. - When in doubt, use `call` over `cast`, to ensure back-pressure - Set appropriate timeouts for `call/3` operations ## Fault Tolerance - Set up processes such that they can handle crashing and being restarted by supervisors - Use `:max_restarts` and `:max_seconds` to prevent restart loops ## Task and Async - Use `Task.Supervisor` for better fault tolerance - Handle task failures with `Task.yield/2` or `Task.shutdown/2` - Set appropriate task timeouts - Use `Task.async_stream/3` for concurrent enumeration with back-pressure ## phoenix:ecto usage ## Ecto Guidelines - **Always** preload Ecto associations in queries when they'll be accessed in templates, ie a message that needs to reference the `message.user.email` - Remember `import Ecto.Query` and other supporting modules when you write `seeds.exs` - `Ecto.Schema` fields always use the `:string` type, even for `:text`, columns, ie: `field :name, :string` - `Ecto.Changeset.validate_number/2` **DOES NOT SUPPORT the `:allow_nil` option**. By default, Ecto validations only run if a change for the given field exists and the change value is not nil, so such as option is never needed - You **must** use `Ecto.Changeset.get_field(changeset, :field)` to access changeset fields - Fields which are set programatically, such as `user_id`, must not be listed in `cast` calls or similar for security purposes. Instead they must be explicitly set when creating the struct - **Always** invoke `mix ecto.gen.migration migration_name_using_underscores` when generating migration files, so the correct timestamp and conventions are applied ## phoenix:elixir usage ## Elixir guidelines - Elixir lists **do not support index based access via the access syntax** **Never do this (invalid)**: i = 0 mylist = ["blue", "green"] mylist[i] Instead, **always** use `Enum.at`, pattern matching, or `List` for index based list access, ie: i = 0 mylist = ["blue", "green"] Enum.at(mylist, i) - Elixir variables are immutable, but can be rebound, so for block expressions like `if`, `case`, `cond`, etc you *must* bind the result of the expression to a variable if you want to use it and you CANNOT rebind the result inside the expression, ie: # INVALID: we are rebinding inside the `if` and the result never gets assigned if connected?(socket) do socket = assign(socket, :val, val) end # VALID: we rebind the result of the `if` to a new variable socket = if connected?(socket) do assign(socket, :val, val) end - **Never** nest multiple modules in the same file as it can cause cyclic dependencies and compilation errors - **Never** use map access syntax (`changeset[:field]`) on structs as they do not implement the Access behaviour by default. For regular structs, you **must** access the fields directly, such as `my_struct.field` or use higher level APIs that are available on the struct if they exist, `Ecto.Changeset.get_field/2` for changesets - Elixir's standard library has everything necessary for date and time manipulation. Familiarize yourself with the common `Time`, `Date`, `DateTime`, and `Calendar` interfaces by accessing their documentation as necessary. **Never** install additional dependencies unless asked or for date/time parsing (which you can use the `date_time_parser` package) - Don't use `String.to_atom/1` on user input (memory leak risk) - Predicate function names should not start with `is_` and should end in a question mark. Names like `is_thing` should be reserved for guards - Elixir's builtin OTP primitives like `DynamicSupervisor` and `Registry`, require names in the child spec, such as `{DynamicSupervisor, name: MyApp.MyDynamicSup}`, then you can use `DynamicSupervisor.start_child(MyApp.MyDynamicSup, child_spec)` - Use `Task.async_stream(collection, callback, options)` for concurrent enumeration with back-pressure. The majority of times you will want to pass `timeout: :infinity` as option ## Mix guidelines - Read the docs and options before using tasks (by using `mix help task_name`) - To debug test failures, run tests in a specific file with `mix test test/my_test.exs` or run all previously failed tests with `mix test --failed` - `mix deps.clean --all` is **almost never needed**. **Avoid** using it unless you have good reason ## Test guidelines - **Always use `start_supervised!/1`** to start processes in tests as it guarantees cleanup between tests - **Avoid** `Process.sleep/1` and `Process.alive?/1` in tests - Instead of sleeping to wait for a process to finish, **always** use `Process.monitor/1` and assert on the DOWN message: ref = Process.monitor(pid) assert_receive {:DOWN, ^ref, :process, ^pid, :normal} - Instead of sleeping to synchronize before the next call, **always** use `_ = :sys.get_state/1` to ensure the process has handled prior messages ## phoenix:html usage ## Phoenix HTML guidelines - Phoenix templates **always** use `~H` or .html.heex files (known as HEEx), **never** use `~E` - **Always** use the imported `Phoenix.Component.form/1` and `Phoenix.Component.inputs_for/1` function to build forms. **Never** use `Phoenix.HTML.form_for` or `Phoenix.HTML.inputs_for` as they are outdated - When building forms **always** use the already imported `Phoenix.Component.to_form/2` (`assign(socket, form: to_form(...))` and `<.form for={@form} id="msg-form">`), then access those forms in the template via `@form[:field]` - **Always** add unique DOM IDs to key elements (like forms, buttons, etc) when writing templates, these IDs can later be used in tests (`<.form for={@form} id="product-form">`) - For "app wide" template imports, you can import/alias into the `my_app_web.ex`'s `html_helpers` block, so they will be available to all LiveViews, LiveComponent's, and all modules that do `use MyAppWeb, :html` (replace "my_app" by the actual app name) - Elixir supports `if/else` but **does NOT support `if/else if` or `if/elsif`**. **Never use `else if` or `elseif` in Elixir**, **always** use `cond` or `case` for multiple conditionals. **Never do this (invalid)**: <%= if condition do %> ... <% else if other_condition %> ... <% end %> Instead **always** do this: <%= cond do %> <% condition -> %> ... <% condition2 -> %> ... <% true -> %> ... <% end %> - HEEx require special tag annotation if you want to insert literal curly's like `{` or `}`. If you want to show a textual code snippet on the page in a `
` or `` block you *must* annotate the parent tag with `phx-no-curly-interpolation`:

      
        let obj = {key: "val"}
      

  Within `phx-no-curly-interpolation` annotated tags, you can use `{` and `}` without escaping them, and dynamic Elixir expressions can still be used with `<%= ... %>` syntax

- HEEx class attrs support lists, but you must **always** use list `[...]` syntax. You can use the class list syntax to conditionally add classes, **always do this for multiple class values**:

      Text

  and **always** wrap `if`'s inside `{...}` expressions with parens, like done above (`if(@other_condition, do: "...", else: "...")`)

  and **never** do this, since it's invalid (note the missing `[` and `]`):

       ...
      => Raises compile syntax error on invalid HEEx attr syntax

- **Never** use `<% Enum.each %>` or non-for comprehensions for generating template content, instead **always** use `<%= for item <- @collection do %>`
- HEEx HTML comments use `<%!-- comment --%>`. **Always** use the HEEx HTML comment syntax for template comments (`<%!-- comment --%>`)
- HEEx allows interpolation via `{...}` and `<%= ... %>`, but the `<%= %>` **only** works within tag bodies. **Always** use the `{...}` syntax for interpolation within tag attributes, and for interpolation of values within tag bodies. **Always** interpolate block constructs (if, cond, case, for) within tag bodies using `<%= ... %>`.

  **Always** do this:

      

        {@my_assign}
        <%= if @some_block_condition do %>
          {@another_assign}
        <% end %>
      


  and **Never** do this – the program will terminate with a syntax error:

      <%!-- THIS IS INVALID NEVER EVER DO THIS --%>
      

        {if @invalid_block_construct do}
        {end}
      




## phoenix:liveview usage
## Phoenix LiveView guidelines

- **Never** use the deprecated `live_redirect` and `live_patch` functions, instead **always** use the `<.link navigate={href}>` and  `<.link patch={href}>` in templates, and `push_navigate` and `push_patch` functions LiveViews
- **Avoid LiveComponent's** unless you have a strong, specific need for them
- LiveViews should be named like `AppWeb.WeatherLive`, with a `Live` suffix. When you go to add LiveView routes to the router, the default `:browser` scope is **already aliased** with the `AppWeb` module, so you can just do `live "/weather", WeatherLive`

### LiveView streams

- **Always** use LiveView streams for collections for assigning regular lists to avoid memory ballooning and runtime termination with the following operations:
  - basic append of N items - `stream(socket, :messages, [new_msg])`
  - resetting stream with new items - `stream(socket, :messages, [new_msg], reset: true)` (e.g. for filtering items)
  - prepend to stream - `stream(socket, :messages, [new_msg], at: -1)`
  - deleting items - `stream_delete(socket, :messages, msg)`

- When using the `stream/3` interfaces in the LiveView, the LiveView template must 1) always set `phx-update="stream"` on the parent element, with a DOM id on the parent element like `id="messages"` and 2) consume the `@streams.stream_name` collection and use the id as the DOM id for each child. For a call like `stream(socket, :messages, [new_msg])` in the LiveView, the template would be:

      

        

          {msg.text}
        

      


- LiveView streams are *not* enumerable, so you cannot use `Enum.filter/2` or `Enum.reject/2` on them. Instead, if you want to filter, prune, or refresh a list of items on the UI, you **must refetch the data and re-stream the entire stream collection, passing reset: true**:

      def handle_event("filter", %{"filter" => filter}, socket) do
        # re-fetch the messages based on the filter
        messages = list_messages(filter)

        {:noreply,
         socket
         |> assign(:messages_empty?, messages == [])
         # reset the stream with the new messages
         |> stream(:messages, messages, reset: true)}
      end

- LiveView streams *do not support counting or empty states*. If you need to display a count, you must track it using a separate assign. For empty states, you can use Tailwind classes:

      

        
        

          {task.name}
        

      


  The above only works if the empty state is the only HTML block alongside the stream for-comprehension.

- When updating an assign that should change content inside any streamed item(s), you MUST re-stream the items
  along with the updated assign:

      def handle_event("edit_message", %{"message_id" => message_id}, socket) do
        message = Chat.get_message!(message_id)
        edit_form = to_form(Chat.change_message(message, %{content: message.content}))

        # re-insert message so @editing_message_id toggle logic takes effect for that stream item
        {:noreply,
         socket
         |> stream_insert(:messages, message)
         |> assign(:editing_message_id, String.to_integer(message_id))
         |> assign(:edit_form, edit_form)}
      end

  And in the template:

      

        

          {message.username}
          <%= if @editing_message_id == message.id do %>
            <%!-- Edit mode --%>
            <.form for={@edit_form} id="edit-form-#{message.id}" phx-submit="save_edit">
              ...
            
          <% end %>
        

      


- **Never** use the deprecated `phx-update="append"` or `phx-update="prepend"` for collections

### LiveView JavaScript interop

- Remember anytime you use `phx-hook="MyHook"` and that JS hook manages its own DOM, you **must** also set the `phx-update="ignore"` attribute
- **Always** provide an unique DOM id alongside `phx-hook` otherwise a compiler error will be raised

LiveView hooks come in two flavors, 1) colocated js hooks for "inline" scripts defined inside HEEx,
and 2) external `phx-hook` annotations where JavaScript object literals are defined and passed to the `LiveSocket` constructor.

#### Inline colocated js hooks

**Never** write raw embedded `

- colocated hooks are automatically integrated into the app.js bundle
- colocated hooks names **MUST ALWAYS** start with a `.` prefix, i.e. `.PhoneNumber`

#### External phx-hook

External JS hooks (`
`) must be placed in `assets/js/` and passed to the
LiveSocket constructor:

    const MyHook = {
      mounted() { ... }
    }
    let liveSocket = new LiveSocket("/live", Socket, {
      hooks: { MyHook }
    });

#### Pushing events between client and server

Use LiveView's `push_event/3` when you need to push events/data to the client for a phx-hook to handle.
**Always** return or rebind the socket on `push_event/3` when pushing events:

    # re-bind socket so we maintain event state to be pushed
    socket = push_event(socket, "my_event", %{...})

    # or return the modified socket directly:
    def handle_event("some_event", _, socket) do
      {:noreply, push_event(socket, "my_event", %{...})}
    end

Pushed events can then be picked up in a JS hook with `this.handleEvent`:

    mounted() {
      this.handleEvent("my_event", data => console.log("from server:", data));
    }

Clients can also push an event to the server and receive a reply with `this.pushEvent`:

    mounted() {
      this.el.addEventListener("click", e => {
        this.pushEvent("my_event", { one: 1 }, reply => console.log("got reply from server:", reply));
      })
    }

Where the server handled it via:

    def handle_event("my_event", %{"one" => 1}, socket) do
      {:reply, %{two: 2}, socket}
    end

### LiveView tests

- `Phoenix.LiveViewTest` module and `LazyHTML` (included) for making your assertions
- Form tests are driven by `Phoenix.LiveViewTest`'s `render_submit/2` and `render_change/2` functions
- Come up with a step-by-step test plan that splits major test cases into small, isolated files. You may start with simpler tests that verify content exists, gradually add interaction tests
- **Always reference the key element IDs you added in the LiveView templates in your tests** for `Phoenix.LiveViewTest` functions like `element/2`, `has_element/2`, selectors, etc
- **Never** tests again raw HTML, **always** use `element/2`, `has_element/2`, and similar: `assert has_element?(view, "#my-form")`
- Instead of relying on testing text content, which can change, favor testing for the presence of key elements
- Focus on testing outcomes rather than implementation details
- Be aware that `Phoenix.Component` functions like `<.form>` might produce different HTML than expected. Test against the output HTML structure, not your mental model of what you expect it to be
- When facing test failures with element selectors, add debug statements to print the actual HTML, but use `LazyHTML` selectors to limit the output, ie:

      html = render(view)
      document = LazyHTML.from_fragment(html)
      matches = LazyHTML.filter(document, "your-complex-selector")
      IO.inspect(matches, label: "Matches")

### Form handling

#### Creating a form from params

If you want to create a form based on `handle_event` params:

    def handle_event("submitted", params, socket) do
      {:noreply, assign(socket, form: to_form(params))}
    end

When you pass a map to `to_form/1`, it assumes said map contains the form params, which are expected to have string keys.

You can also specify a name to nest the params:

    def handle_event("submitted", %{"user" => user_params}, socket) do
      {:noreply, assign(socket, form: to_form(user_params, as: :user))}
    end

#### Creating a form from changesets

When using changesets, the underlying data, form params, and errors are retrieved from it. The `:as` option is automatically computed too. E.g. if you have a user schema:

    defmodule MyApp.Users.User do
      use Ecto.Schema
      ...
    end

And then you create a changeset that you pass to `to_form`:

    %MyApp.Users.User{}
    |> Ecto.Changeset.change()
    |> to_form()

Once the form is submitted, the params will be available under `%{"user" => user_params}`.

In the template, the form form assign can be passed to the `<.form>` function component:

    <.form for={@form} id="todo-form" phx-change="validate" phx-submit="save">
      <.input field={@form[:field]} type="text" />
    

Always give the form an explicit, unique DOM ID, like `id="todo-form"`.

#### Avoiding form errors

**Always** use a form assigned via `to_form/2` in the LiveView, and the `<.input>` component in the template. In the template **always access forms this**:

    <%!-- ALWAYS do this (valid) --%>
    <.form for={@form} id="my-form">
      <.input field={@form[:field]} type="text" />
    

And **never** do this:

    <%!-- NEVER do this (invalid) --%>
    <.form for={@changeset} id="my-form">
      <.input field={@changeset[:field]} type="text" />
    

- You are FORBIDDEN from accessing the changeset in the template as it will cause errors
- **Never** use `<.form let={f} ...>` in the template, instead **always use `<.form for={@form} ...>`**, then drive all form references from the form assign as in `@form[:field]`. The UI should **always** be driven by a `to_form/2` assigned in the LiveView module that is derived from a changeset



## phoenix:phoenix usage
## Phoenix guidelines

- Remember Phoenix router `scope` blocks include an optional alias which is prefixed for all routes within the scope. **Always** be mindful of this when creating routes within a scope to avoid duplicate module prefixes.

- You **never** need to create your own `alias` for route definitions! The `scope` provides the alias, ie:

      scope "/admin", AppWeb.Admin do
        pipe_through :browser

        live "/users", UserLive, :index
      end

  the UserLive route would point to the `AppWeb.Admin.UserLive` module

- `Phoenix.View` no longer is needed or included with Phoenix, don't use it



## usage_rules usage
_A config-driven dev tool for Elixir projects to manage AGENTS.md files and agent skills from dependencies_

## Using Usage Rules

Many packages have usage rules, which you should *thoroughly* consult before taking any
action. These usage rules contain guidelines and rules *directly from the package authors*.
They are your best source of knowledge for making decisions.

## Modules & functions in the current app and dependencies

When looking for docs for modules & functions that are dependencies of the current project,
or for Elixir itself, use `mix usage_rules.docs`

```
# Search a whole module
mix usage_rules.docs Enum

# Search a specific function
mix usage_rules.docs Enum.zip

# Search a specific function & arity
mix usage_rules.docs Enum.zip/1
```


## Searching Documentation

You should also consult the documentation of any tools you are using, early and often. The best 
way to accomplish this is to use the `usage_rules.search_docs` mix task. Once you have
found what you are looking for, use the links in the search results to get more detail. For example:

```
# Search docs for all packages in the current application, including Elixir
mix usage_rules.search_docs Enum.zip

# Search docs for specific packages
mix usage_rules.search_docs Req.get -p req

# Search docs for multi-word queries
mix usage_rules.search_docs "making requests" -p req

# Search only in titles (useful for finding specific functions/modules)
mix usage_rules.search_docs "Enum.zip" --query-by title
```




## usage_rules:elixir usage
# Elixir Core Usage Rules

## Pattern Matching
- Use pattern matching over conditional logic when possible
- Prefer to match on function heads instead of using `if`/`else` or `case` in function bodies
- `%{}` matches ANY map, not just empty maps. Use `map_size(map) == 0` guard to check for truly empty maps

## Error Handling
- Use `{:ok, result}` and `{:error, reason}` tuples for operations that can fail
- Avoid raising exceptions for control flow
- Use `with` for chaining operations that return `{:ok, _}` or `{:error, _}`

## Common Mistakes to Avoid
- Elixir has no `return` statement, nor early returns. The last expression in a block is always returned.
- Don't use `Enum` functions on large collections when `Stream` is more appropriate
- Avoid nested `case` statements - refactor to a single `case`, `with` or separate functions
- Don't use `String.to_atom/1` on user input (memory leak risk)
- Lists and enumerables cannot be indexed with brackets. Use pattern matching or `Enum` functions
- Prefer `Enum` functions like `Enum.reduce` over recursion
- When recursion is necessary, prefer to use pattern matching in function heads for base case detection
- Using the process dictionary is typically a sign of unidiomatic code
- Only use macros if explicitly requested
- There are many useful standard library functions, prefer to use them where possible

## Function Design
- Use guard clauses: `when is_binary(name) and byte_size(name) > 0`
- Prefer multiple function clauses over complex conditional logic
- Name functions descriptively: `calculate_total_price/2` not `calc/2`
- Predicate function names should not start with `is` and should end in a question mark.
- Names like `is_thing` should be reserved for guards

## Data Structures
- Use structs over maps when the shape is known: `defstruct [:name, :age]`
- Prefer keyword lists for options: `[timeout: 5000, retries: 3]`
- Use maps for dynamic key-value data
- Prefer to prepend to lists `[new | list]` not `list ++ [new]`

## Mix Tasks

- Use `mix help` to list available mix tasks
- Use `mix help task_name` to get docs for an individual task
- Read the docs and options fully before using tasks

## Testing
- Run tests in a specific file with `mix test test/my_test.exs` and a specific test with the line number `mix test path/to/test.exs:123`
- Limit the number of failed tests with `mix test --max-failures n`
- Use `@tag` to tag specific tests, and `mix test --only tag` to run only those tests
- Use `assert_raise` for testing expected exceptions: `assert_raise ArgumentError, fn -> invalid_function() end`
- Use `mix help test` to for full documentation on running tests

## Debugging

- Use `dbg/1` to print values while debugging. This will display the formatted value and other relevant information in the console.



## usage_rules:otp usage
# OTP Usage Rules

## GenServer Best Practices
- Keep state simple and serializable
- Handle all expected messages explicitly
- Use `handle_continue/2` for post-init work
- Implement proper cleanup in `terminate/2` when necessary

## Process Communication
- Use `GenServer.call/3` for synchronous requests expecting replies
- Use `GenServer.cast/2` for fire-and-forget messages.
- When in doubt, use `call` over `cast`, to ensure back-pressure
- Set appropriate timeouts for `call/3` operations

## Fault Tolerance
- Set up processes such that they can handle crashing and being restarted by supervisors
- Use `:max_restarts` and `:max_seconds` to prevent restart loops

## Task and Async
- Use `Task.Supervisor` for better fault tolerance
- Handle task failures with `Task.yield/2` or `Task.shutdown/2`
- Set appropriate task timeouts
- Use `Task.async_stream/3` for concurrent enumeration with back-pressure



## usage_rules usage
_A config-driven dev tool for Elixir projects to manage AGENTS.md files and agent skills from dependencies_

## Using Usage Rules

Many packages have usage rules, which you should *thoroughly* consult before taking any
action. These usage rules contain guidelines and rules *directly from the package authors*.
They are your best source of knowledge for making decisions.

## Modules & functions in the current app and dependencies

When looking for docs for modules & functions that are dependencies of the current project,
or for Elixir itself, use `mix usage_rules.docs`

```
# Search a whole module
mix usage_rules.docs Enum

# Search a specific function
mix usage_rules.docs Enum.zip

# Search a specific function & arity
mix usage_rules.docs Enum.zip/1
```


## Searching Documentation

You should also consult the documentation of any tools you are using, early and often. The best 
way to accomplish this is to use the `usage_rules.search_docs` mix task. Once you have
found what you are looking for, use the links in the search results to get more detail. For example:

```
# Search docs for all packages in the current application, including Elixir
mix usage_rules.search_docs Enum.zip

# Search docs for specific packages
mix usage_rules.search_docs Req.get -p req

# Search docs for multi-word queries
mix usage_rules.search_docs "making requests" -p req

# Search only in titles (useful for finding specific functions/modules)
mix usage_rules.search_docs "Enum.zip" --query-by title
```




## usage_rules:elixir usage
# Elixir Core Usage Rules

## Pattern Matching
- Use pattern matching over conditional logic when possible
- Prefer to match on function heads instead of using `if`/`else` or `case` in function bodies
- `%{}` matches ANY map, not just empty maps. Use `map_size(map) == 0` guard to check for truly empty maps

## Error Handling
- Use `{:ok, result}` and `{:error, reason}` tuples for operations that can fail
- Avoid raising exceptions for control flow
- Use `with` for chaining operations that return `{:ok, _}` or `{:error, _}`

## Common Mistakes to Avoid
- Elixir has no `return` statement, nor early returns. The last expression in a block is always returned.
- Don't use `Enum` functions on large collections when `Stream` is more appropriate
- Avoid nested `case` statements - refactor to a single `case`, `with` or separate functions
- Don't use `String.to_atom/1` on user input (memory leak risk)
- Lists and enumerables cannot be indexed with brackets. Use pattern matching or `Enum` functions
- Prefer `Enum` functions like `Enum.reduce` over recursion
- When recursion is necessary, prefer to use pattern matching in function heads for base case detection
- Using the process dictionary is typically a sign of unidiomatic code
- Only use macros if explicitly requested
- There are many useful standard library functions, prefer to use them where possible

## Function Design
- Use guard clauses: `when is_binary(name) and byte_size(name) > 0`
- Prefer multiple function clauses over complex conditional logic
- Name functions descriptively: `calculate_total_price/2` not `calc/2`
- Predicate function names should not start with `is` and should end in a question mark.
- Names like `is_thing` should be reserved for guards

## Data Structures
- Use structs over maps when the shape is known: `defstruct [:name, :age]`
- Prefer keyword lists for options: `[timeout: 5000, retries: 3]`
- Use maps for dynamic key-value data
- Prefer to prepend to lists `[new | list]` not `list ++ [new]`

## Mix Tasks

- Use `mix help` to list available mix tasks
- Use `mix help task_name` to get docs for an individual task
- Read the docs and options fully before using tasks

## Testing
- Run tests in a specific file with `mix test test/my_test.exs` and a specific test with the line number `mix test path/to/test.exs:123`
- Limit the number of failed tests with `mix test --max-failures n`
- Use `@tag` to tag specific tests, and `mix test --only tag` to run only those tests
- Use `assert_raise` for testing expected exceptions: `assert_raise ArgumentError, fn -> invalid_function() end`
- Use `mix help test` to for full documentation on running tests

## Debugging

- Use `dbg/1` to print values while debugging. This will display the formatted value and other relevant information in the console.



## usage_rules:otp usage
# OTP Usage Rules

## GenServer Best Practices
- Keep state simple and serializable
- Handle all expected messages explicitly
- Use `handle_continue/2` for post-init work
- Implement proper cleanup in `terminate/2` when necessary

## Process Communication
- Use `GenServer.call/3` for synchronous requests expecting replies
- Use `GenServer.cast/2` for fire-and-forget messages.
- When in doubt, use `call` over `cast`, to ensure back-pressure
- Set appropriate timeouts for `call/3` operations

## Fault Tolerance
- Set up processes such that they can handle crashing and being restarted by supervisors
- Use `:max_restarts` and `:max_seconds` to prevent restart loops

## Task and Async
- Use `Task.Supervisor` for better fault tolerance
- Handle task failures with `Task.yield/2` or `Task.shutdown/2`
- Set appropriate task timeouts
- Use `Task.async_stream/3` for concurrent enumeration with back-pressure



## fluxon usage
_Fluxon UI Components_

@deps/fluxon/usage-rules.md