Feat: context-guru context-engineering plugin + demo

Add context-guru as an in-process AuthBridge outbound plugin that compacts an
agent's LLM request context (tool outputs) before it is forwarded upstream, plus
a runnable end-to-end demo on Kagenti.

- authlib/plugins/contextguru: OnRequest compaction via apply.BodyWithModel +
  SetBody; slog logging; WritesBody + RequiresAny:[inference-parser]; tests.
- cmd/authbridge-{proxy,envoy}: build-tag-gated plugin registration.
- demos/context-guru: multi-transaction audit demo (off/observe/enforce),
  README with diagrams + config reference, run.sh.
- demos/finance-sparc/finance-mcp: two large-output tools for realistic context.

Depends on the published github.com/kagenti/context-guru module. Toolchain
bumped to go 1.26.4 (required by context-guru via bifrost/core); Dockerfile
builders moved to golang:1.26-alpine (digest-pinned).

Relates to #659, #641.

Assisted-By: Claude (Anthropic AI) <noreply@anthropic.com>
Signed-off-by: Osher-Elhadad <Osher.Elhadad@ibm.com>

Author: Osher-Elhadad

authbridge/authlib/go.mod

@@ -1,12 +1,14 @@
 module github.com/kagenti/kagenti-extensions/authbridge/authlib
 
-go 1.25.0
+go 1.26.4
 
 require (
 	github.com/envoyproxy/go-control-plane/envoy v1.37.0
 	github.com/fsnotify/fsnotify v1.10.1
 	github.com/gobwas/glob v0.2.3
+	github.com/kagenti/context-guru v0.0.0-20260713113308-b624f2c3d8c2
 	github.com/lestrrat-go/jwx/v2 v2.1.6
+	github.com/maximhq/bifrost/core v1.7.0
 	github.com/open-policy-agent/opa v1.4.2
 	github.com/spiffe/go-spiffe/v2 v2.6.0
 	golang.org/x/net v0.56.0
@@ -20,15 +22,38 @@ require (
 	github.com/AdaLogics/go-fuzz-headers v0.0.0-20230811130428-ced1acdcaa24 // indirect
 	github.com/Microsoft/go-winio v0.6.2 // indirect
 	github.com/agnivade/levenshtein v1.2.1 // indirect
+	github.com/alexaandru/go-sitter-forest/c v1.9.4 // indirect
+	github.com/alexaandru/go-sitter-forest/c_sharp v1.9.6 // indirect
+	github.com/alexaandru/go-sitter-forest/cpp v1.9.5 // indirect
+	github.com/alexaandru/go-sitter-forest/go v1.9.4 // indirect
+	github.com/alexaandru/go-sitter-forest/java v1.9.5 // indirect
+	github.com/alexaandru/go-sitter-forest/javascript v1.9.2 // indirect
+	github.com/alexaandru/go-sitter-forest/kotlin v1.9.4 // indirect
+	github.com/alexaandru/go-sitter-forest/php v1.9.5 // indirect
+	github.com/alexaandru/go-sitter-forest/python v1.9.10 // indirect
+	github.com/alexaandru/go-sitter-forest/ruby v1.9.3 // indirect
+	github.com/alexaandru/go-sitter-forest/rust v1.9.13 // indirect
+	github.com/alexaandru/go-sitter-forest/scala v1.9.8 // indirect
+	github.com/alexaandru/go-sitter-forest/swift v1.9.5 // indirect
+	github.com/alexaandru/go-sitter-forest/tsx v1.9.2 // indirect
+	github.com/alexaandru/go-sitter-forest/typescript v1.9.4 // indirect
+	github.com/andybalholm/brotli v1.2.2 // indirect
+	github.com/bahlo/generic-list-go v0.2.0 // indirect
 	github.com/beorn7/perks v1.0.1 // indirect
+	github.com/buger/jsonparser v1.1.2 // indirect
 	github.com/bytecodealliance/wasmtime-go/v3 v3.0.2 // indirect
+	github.com/bytedance/gopkg v0.1.3 // indirect
+	github.com/bytedance/sonic v1.15.1 // indirect
+	github.com/bytedance/sonic/loader v0.5.1 // indirect
 	github.com/cespare/xxhash/v2 v2.3.0 // indirect
+	github.com/cloudwego/base64x v0.1.6 // indirect
 	github.com/cncf/xds/go v0.0.0-20260202195803-dba9d589def2 // indirect
 	github.com/containerd/containerd v1.7.32 // indirect
 	github.com/containerd/errdefs v1.0.0 // indirect
 	github.com/containerd/log v0.1.0 // indirect
 	github.com/containerd/platforms v0.2.1 // indirect
 	github.com/decred/dcrd/dcrec/secp256k1/v4 v4.4.0 // indirect
+	github.com/dlclark/regexp2 v1.11.5 // indirect
 	github.com/envoyproxy/protoc-gen-validate v1.3.3 // indirect
 	github.com/felixge/httpsnoop v1.0.4 // indirect
 	github.com/go-ini/ini v1.67.0 // indirect
@@ -39,12 +64,17 @@ require (
 	github.com/google/uuid v1.6.0 // indirect
 	github.com/gorilla/mux v1.8.1 // indirect
 	github.com/grpc-ecosystem/grpc-gateway/v2 v2.27.2 // indirect
-	github.com/klauspost/compress v1.18.0 // indirect
+	github.com/invopop/jsonschema v0.13.0 // indirect
+	github.com/klauspost/compress v1.18.6 // indirect
+	github.com/klauspost/cpuid/v2 v2.3.0 // indirect
 	github.com/lestrrat-go/blackmagic v1.0.3 // indirect
 	github.com/lestrrat-go/httpcc v1.0.1 // indirect
 	github.com/lestrrat-go/httprc v1.0.6 // indirect
 	github.com/lestrrat-go/iter v1.0.2 // indirect
 	github.com/lestrrat-go/option v1.0.1 // indirect
+	github.com/mailru/easyjson v0.9.1 // indirect
+	github.com/mark3labs/mcp-go v0.43.2 // indirect
+	github.com/mattn/go-pointer v0.0.1 // indirect
 	github.com/moby/locker v1.0.1 // indirect
 	github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 // indirect
 	github.com/opencontainers/go-digest v1.0.0 // indirect
@@ -57,21 +87,35 @@ require (
 	github.com/rcrowley/go-metrics v0.0.0-20200313005456-10cdbea86bc0 // indirect
 	github.com/segmentio/asm v1.2.0 // indirect
 	github.com/sirupsen/logrus v1.9.3 // indirect
+	github.com/spf13/cast v1.10.0 // indirect
 	github.com/tchap/go-patricia/v2 v2.3.2 // indirect
+	github.com/tidwall/gjson v1.18.0 // indirect
+	github.com/tidwall/match v1.1.1 // indirect
+	github.com/tidwall/pretty v1.2.1 // indirect
+	github.com/tidwall/sjson v1.2.5 // indirect
+	github.com/tiktoken-go/tokenizer v0.7.0 // indirect
+	github.com/tree-sitter/go-tree-sitter v0.25.0 // indirect
+	github.com/twitchyliquid64/golang-asm v0.15.1 // indirect
+	github.com/valyala/bytebufferpool v1.0.0 // indirect
+	github.com/valyala/fasthttp v1.71.0 // indirect
+	github.com/wk8/go-ordered-map/v2 v2.1.8 // indirect
 	github.com/xeipuuv/gojsonpointer v0.0.0-20190905194746-02993c407bfb // indirect
 	github.com/xeipuuv/gojsonreference v0.0.0-20180127040603-bd5ef7bd5415 // indirect
 	github.com/yashtewari/glob-intersection v0.2.0 // indirect
+	github.com/yosida95/uritemplate/v3 v3.0.2 // indirect
 	go.opentelemetry.io/auto/sdk v1.2.1 // indirect
-	go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.60.0 // indirect
+	go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.61.0 // indirect
 	go.opentelemetry.io/otel v1.43.0 // indirect
 	go.opentelemetry.io/otel/metric v1.43.0 // indirect
 	go.opentelemetry.io/otel/sdk v1.43.0 // indirect
 	go.opentelemetry.io/otel/trace v1.43.0 // indirect
+	go.starlark.net v0.0.0-20260708150628-5395d018f003 // indirect
+	golang.org/x/arch v0.23.0 // indirect
 	golang.org/x/crypto v0.53.0 // indirect
 	golang.org/x/sync v0.21.0 // indirect
 	golang.org/x/text v0.38.0 // indirect
 	golang.org/x/time v0.12.0 // indirect
-	google.golang.org/protobuf v1.36.11 // indirect
+	google.golang.org/protobuf v1.36.12-0.20260120151049-f2248ac996af // indirect
 	oras.land/oras-go/v2 v2.5.0 // indirect
 	sigs.k8s.io/yaml v1.4.0 // indirect
 )