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>

core/http/endpoints/openai/list_capabilities.go

@@ -36,6 +36,12 @@ func ListModelCapabilitiesEndpoint(bcl *config.ModelConfigLoader, ml *model.Mode
 		for _, m := range modelNames {
 			entry := schema.ModelCapabilities{ID: m, Object: "model"}
 			if cfg, ok := modelConfigFor(bcl, m); ok {
+				// Mirror the request path: SetDefaults applies the application
+				// default only when the model leaves context_size unset. An
+				// explicit 0 or -1 falls through to the backend fallback there.
+				if cfg.ContextSize == nil && appConfig != nil && appConfig.ContextSize > 0 {
+					cfg.ContextSize = &appConfig.ContextSize
+				}
 				entry.Capabilities = cfg.Capabilities()
 				entry.ThreeDOperations = cfg.ThreeDOperations()
 				entry.InputModalities = cfg.InputModalities()

core/http/endpoints/openai/list_capabilities_test.go

@@ -160,6 +160,33 @@ parameters:
 		Expect(entry).NotTo(BeNil())
 		Expect(entry.ContextSize).To(Equal(backend.DefaultContextSize))
 	})
+
+	It("uses application config context size when model context_size is unset", func() {
+		writeConfig("llm-app-default", `
+name: llm-app-default
+backend: llama-cpp
+parameters:
+  model: model.gguf
+`)
+		appConf.ContextSize = 8192
+		entry := entryFor(call(), "llm-app-default")
+		Expect(entry).NotTo(BeNil())
+		Expect(entry.ContextSize).To(Equal(8192))
+	})
+
+	It("keeps the backend fallback when the model sets a non-positive context_size", func() {
+		writeConfig("llm-explicit-zero", `
+name: llm-explicit-zero
+backend: llama-cpp
+context_size: 0
+parameters:
+  model: model.gguf
+`)
+		appConf.ContextSize = 8192
+		entry := entryFor(call(), "llm-explicit-zero")
+		Expect(entry).NotTo(BeNil())
+		Expect(entry.ContextSize).To(Equal(backend.DefaultContextSize))
+	})
 	It("reports an alias with its target's capabilities and context_size", func() {
 		writeConfig("real-llm", `
 name: real-llm