server: add presets (config) when using multiple models (#17859)

* llama-server: recursive GGUF loading

Replace flat directory scan with recursive traversal using
std::filesystem::recursive_directory_iterator. Support for
nested vendor/model layouts (e.g. vendor/model/*.gguf).
Model name now reflects the relative path within --models-dir
instead of just the filename. Aggregate files by parent
directory via std::map before constructing local_model

* server : router config POC (INI-based per-model settings)

* server: address review feedback from @aldehir and @ngxson

PEG parser usage improvements:
- Simplify parser instantiation (remove arena indirection)
- Optimize grammar usage (ws instead of zero_or_more, remove optional wrapping)
- Fix last line without newline bug (+ operator instead of <<)
- Remove redundant end position check

Feature scope:
- Remove auto-reload feature (will be separate PR per @ngxson)
- Keep config.ini auto-creation and template generation
- Preserve per-model customization logic

Co-authored-by: aldehir <aldehir@users.noreply.github.com>
Co-authored-by: ngxson <ngxson@users.noreply.github.com>

* server: adopt aldehir's line-oriented PEG parser

Complete rewrite of INI parser grammar and visitor:
- Use p.chars(), p.negate(), p.any() instead of p.until()
- Support end-of-line comments (key=value # comment)
- Handle EOF without trailing newline correctly
- Strict identifier validation ([a-zA-Z_][a-zA-Z0-9_.-]*)
- Simplified visitor (no pending state, no trim needed)
- Grammar handles whitespace natively via eol rule

Business validation preserved:
- Reject section names starting with LLAMA_ARG_*
- Accept only keys starting with LLAMA_ARG_*
- Require explicit section before key-value pairs

Co-authored-by: aldehir <aldehir@users.noreply.github.com>

* server: fix CLI/env duplication in child processes

Children now receive minimal CLI args (executable, model, port, alias)
instead of inheriting all router args. Global settings pass through
LLAMA_ARG_* environment variables only, eliminating duplicate config
warnings.

Fixes: Router args like -ngl, -fa were passed both via CLI and env,
causing 'will be overwritten' warnings on every child spawn

* add common/preset.cpp

* fix compile

* cont

* allow custom-path models

* add falsey check

* server: fix router model discovery and child process spawning

- Sanitize model names: replace / and \ with _ for display
- Recursive directory scan with relative path storage
- Convert relative paths to absolute when spawning children
- Filter router control args from child processes
- Refresh args after port assignment for correct port value
- Fallback preset lookup for compatibility
- Fix missing argv[0]: store server binary path before base_args parsing

* Revert "server: fix router model discovery and child process spawning"

This reverts commit e3832b42eeea7fcb108995966c7584479f745857.

* clarify about "no-" prefix

* correct render_args() to include binary path

* also remove arg LLAMA_ARG_MODELS_PRESET for child

* add co-author for ini parser code

Co-authored-by: aldehir <hello@alde.dev>

* also set LLAMA_ARG_HOST

* add CHILD_ADDR

* Remove dead code

---------

Co-authored-by: aldehir <aldehir@users.noreply.github.com>
Co-authored-by: ngxson <ngxson@users.noreply.github.com>
Co-authored-by: Xuan Son Nguyen <son@huggingface.co>
Co-authored-by: aldehir <hello@alde.dev>

tools/server/README.md

@@ -1369,6 +1369,11 @@ llama-server
 
 ### Model sources
 
+There are 3 possible sources for model files:
+1. Cached models (controlled by the `LLAMA_CACHE` environment variable)
+2. Custom model directory (set via the `--models-dir` argument)
+3. Custom preset (set via the `--models-preset` argument)
+
 By default, the router looks for models in the cache. You can add Hugging Face models to the cache with:
 
 ```sh
@@ -1413,6 +1418,51 @@ llama-server -ctx 8192 -n 1024 -np 2
 
 Note: model instances inherit both command line arguments and environment variables from the router server.
 
+Alternatively, you can also add GGUF based preset (see next section)
+
+### Model presets
+
+Model presets allow advanced users to define custom configurations using an `.ini` file:
+
+```sh
+llama-server --models-preset ./my-models.ini
+```
+
+Each section in the file defines a new preset. Keys within a section correspond to command-line arguments (without leading dashes). For example, the argument `--n-gpu-layer 123` is written as `n-gpu-layer = 123`.
+
+Short argument forms (e.g., `c`, `ngl`) and environment variable names (e.g., `LLAMA_ARG_N_GPU_LAYERS`) are also supported as keys.
+
+Example:
+
+```ini
+version = 1
+
+; If the key corresponds to an existing model on the server,
+; this will be used as the default config for that model
+[ggml-org/MY-MODEL-GGUF:Q8_0]
+; string value
+chat-template = chatml
+; numeric value
+n-gpu-layer = 123
+; flag value (for certain flags, you need to use the "no-" prefix for negation)
+jinja = true
+; shorthand argument (for example, context size)
+c = 4096
+; environment variable name
+LLAMA_ARG_CACHE_RAM = 0
+; file paths are relative to server's CWD
+model-draft = ./my-models/draft.gguf
+; but it's RECOMMENDED to use absolute path
+model-draft = /Users/abc/my-models/draft.gguf
+
+; If the key does NOT correspond to an existing model,
+; you need to specify at least the model path
+[custom_model]
+model = /Users/abc/my-awesome-model-Q4_K_M.gguf
+```
+
+Note: some arguments are controlled by router (e.g., host, port, API key, HF repo, model alias). They will be removed or overwritten upload loading.
+
 ### Routing requests
 
 Requests are routed according to the requested model name.