fix(models): fallback to application config default context size in /v1/models/capabilities (#12202) (#12216)

* fix(models): fallback to application config default context size (#12202)

Honor appConfig.ContextSize in /v1/models/capabilities when model context_size is unset.

* docs(models): explain context size fallback

Describe the application default used by capability discovery and
preserve the distinction between total context and per-request limits.

Assisted-by: Codex:GPT-6

* fix(models): apply the default context size only when context_size is unset

The request path applies the application default context size only
when a model leaves context_size unset. An explicit 0 or -1 falls
through to the backend fallback. The capabilities endpoint now does
the same, so it reports the value the backend uses.

Assisted-by: Claude:claude-opus-5-5 [Claude Code]
Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

---------

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>
Co-authored-by: localai-org-maint-bot <306269227+localai-org-maint-bot@users.noreply.github.com>
Co-authored-by: Ettore Di Giacinto <mudler@localai.io>

docs/content/features/api-discovery.md

@@ -141,6 +141,11 @@ curl http://localhost:8080/api/instructions/config-management?format=json
 
 An additive, LocalAI-specific superset of `/v1/models`. It returns the same set of models but enriches each entry with the **capabilities** the model supports and the **input/output modalities** it accepts and produces. Use it to decide, before sending a request, whether a given model can take an image, audio, or video attachment directly - or whether the input needs converting/transcribing first.
 
+The reported `context_size` uses a positive model-level value first.
+If the model does not set `context_size`, it uses **Settings → Performance → Default Context Size** when positive.
+Otherwise, it uses the backend fallback of 4096 tokens.
+For llama.cpp with separate KV caches, the reported value accounts for the number of parallel slots.
+
 Because it is purely additive, clients that only understand `/v1/models` keep working unchanged; they simply never call this route.
 
 ```bash