setup usage_rules

CLAUDE.md

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+<!-- usage-rules-start -->
+<!-- usage_rules-start -->
+## 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-end -->
+<!-- usage_rules:elixir-start -->
+## 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:elixir-end -->
+<!-- usage_rules:otp-start -->
+## 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:otp-end -->
+<!-- usage-rules-end -->