From b4703e5041365c21222a4d36114218ab153776e7 Mon Sep 17 00:00:00 2001
From: Richard McDaniel <1130888+rmcdaniel@users.noreply.github.com>
Date: Sat, 14 Nov 2026 11:37:13 +0000
Subject: [PATCH 1/3] Allow modern hosts to omit the default compiler
 compatibility pin

---
 Cargo.toml | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index cd9b06a..d5eede5 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -107,7 +107,11 @@ name = "durable_workflow"
 path = "src/lib.rs"
 
 [features]
-default = []
+default = ["msrv-1-86"]
+# Keep the legacy compiler dependency pin for default SDK builds. A host
+# already using a newer Rust toolchain may disable default features to
+# compose with libraries that require a newer builder macro.
+msrv-1-86 = ["dep:bon"]
 telemetry = ["dep:opentelemetry", "dep:opentelemetry_sdk"]
 metrics-prometheus = ["dep:prometheus"]
 
@@ -120,7 +124,7 @@ tracing = { version = "0.1", default-features = false, features = ["std"] }
 apache-avro = { version = "0.21", default-features = false }
 base64 = "0.22"
 # Keep apache-avro's dependency resolution compatible with the Rust 1.86 MSRV.
-bon = { version = "=3.8.1", default-features = false }
+bon = { version = "=3.8.1", default-features = false, optional = true }
 chrono = { version = "0.4", default-features = false, features = ["alloc"] }
 futures-util = "0.3"
 # Keep reqwest's IDNA dependency resolution compatible with the Rust 1.86 MSRV.

From ff75c2a59029cc5c6ab510ca5af2e3acc06ae7b4 Mon Sep 17 00:00:00 2001
From: Richard McDaniel <1130888+rmcdaniel@users.noreply.github.com>
Date: Sat, 14 Nov 2026 11:51:05 +0000
Subject: [PATCH 2/3] Document compiler opt-out and test native dependency
 composition

---
 .github/workflows/ci.yml               |  6 ++++++
 CHANGELOG.md                           |  6 ++++++
 README.md                              | 10 ++++++++++
 scripts/ci/README.md                   |  3 ++-
 scripts/ci/check-native-composition.sh | 26 ++++++++++++++++++++++++++
 tests/native-composition/.gitignore    |  2 ++
 tests/native-composition/Cargo.toml    | 15 +++++++++++++++
 tests/native-composition/src/main.rs   |  4 ++++
 8 files changed, 71 insertions(+), 1 deletion(-)
 create mode 100755 scripts/ci/check-native-composition.sh
 create mode 100644 tests/native-composition/.gitignore
 create mode 100644 tests/native-composition/Cargo.toml
 create mode 100644 tests/native-composition/src/main.rs

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 9c6f271..191c5f0 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -231,6 +231,12 @@ jobs:
           key: ${{ runner.os }}-${{ runner.arch }}-sdk-tests-v2-lines-${{ steps.toolchain.outputs.cachekey }}-${{ steps.dependencies.outputs.key }}
       - run: cargo fmt --all --check
       - run: cargo test --locked --all-targets --all-features
+      - name: Check explicit Rust 1.86 compatibility without default features
+        if: ${{ matrix.rust == '1.86.0' }}
+        run: cargo check --locked --no-default-features --features msrv-1-86
+      - name: Check modern native host dependency composition
+        if: ${{ matrix.rust == 'stable' }}
+        run: scripts/ci/check-native-composition.sh
       - name: Qualify ready-age metrics against the published native Server
         if: ${{ matrix.rust == '1.86.0' }}
         run: python3 scripts/ci/qualify-worker-metrics.py
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 13be16f..d4de3c7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,12 @@
 
 ## Unreleased
 
+- The default `msrv-1-86` feature retains the existing compiler-compatibility
+  dependency pin. Modern hosts can disable it to compose the SDK with native
+  Server's newer official Avro dependency. Rust 1.86 consumers that disable
+  default features must explicitly enable `msrv-1-86`; an unpinned fresh graph
+  can require a newer compiler.
+
 - Service activity contexts expose negotiated, immutable acknowledged-heartbeat
   checkpoint details and a typed acknowledgement time. Unsupported claims stay
   unavailable, separately from a supported claim with no checkpoint. Heartbeat
diff --git a/README.md b/README.md
index 0c73867..0d07faa 100644
--- a/README.md
+++ b/README.md
@@ -1214,6 +1214,16 @@ negotiation remain required for individual features.
 
 ## Development
 
+Default builds enable `msrv-1-86`, which keeps the builder-macro dependency pin
+needed by fresh Rust 1.86 consumers. If you disable default features and still
+require Rust 1.86, explicitly enable `msrv-1-86`.
+
+A host on a newer compiler can omit that feature to compose the SDK with the
+native Server library and its newer official Avro dependency. Without the pin,
+fresh dependency resolution can require a newer compiler. The native composition
+check uses Rust 1.88 or later; this opt-out does not change SDK runtime APIs or
+protocol negotiation.
+
 ```sh
 cargo fmt --all --check
 cargo test --locked --all-targets --all-features
diff --git a/scripts/ci/README.md b/scripts/ci/README.md
index bf2ecf1..dbce270 100644
--- a/scripts/ci/README.md
+++ b/scripts/ci/README.md
@@ -1,10 +1,11 @@
 # CI support
 
-These scripts support four public repository checks:
+These scripts support public repository checks:
 
 - replay and codec regression-corpus validation;
 - Apache Avro interoperability and performance checks;
 - publishable crate and fresh-consumer verification;
+- compiler compatibility and native host dependency composition;
 - API documentation, analytics, navigation, and base-URL checks.
 
 The release workflow uses the crates.io publishing scripts after an immutable
diff --git a/scripts/ci/check-native-composition.sh b/scripts/ci/check-native-composition.sh
new file mode 100755
index 0000000..060d85e
--- /dev/null
+++ b/scripts/ci/check-native-composition.sh
@@ -0,0 +1,26 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+composition_root="$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")/../.." && pwd)"
+composition_manifest="$composition_root/tests/native-composition/Cargo.toml"
+composition_log="$(mktemp)"
+trap 'rm -f -- "$composition_log"' EXIT
+
+# The modern host opts out; Cargo must compile both official Avro versions.
+cargo check --manifest-path "$composition_manifest"
+
+# Re-enabling the legacy compiler pin must retain the real resolver refusal.
+if cargo metadata --format-version 1 --manifest-path "$composition_manifest" \
+    --features sdk-msrv-pin >"$composition_log" 2>&1; then
+    printf 'native composition unexpectedly accepted the incompatible MSRV pin\n' >&2
+    exit 1
+fi
+python3 -I -S -B - "$composition_log" <<'PY'
+import pathlib
+import sys
+
+error = pathlib.Path(sys.argv[1]).read_text()
+if not all(value in error for value in ("bon", "3.8.1", "3.9.1")):
+    raise SystemExit("native composition failed without the expected bon constraint conflict")
+print("modern composition builds; the explicit MSRV pin retains its resolver refusal")
+PY
diff --git a/tests/native-composition/.gitignore b/tests/native-composition/.gitignore
new file mode 100644
index 0000000..042776a
--- /dev/null
+++ b/tests/native-composition/.gitignore
@@ -0,0 +1,2 @@
+/Cargo.lock
+/target/
diff --git a/tests/native-composition/Cargo.toml b/tests/native-composition/Cargo.toml
new file mode 100644
index 0000000..6a7e5fb
--- /dev/null
+++ b/tests/native-composition/Cargo.toml
@@ -0,0 +1,15 @@
+[package]
+name = "durable-workflow-native-composition-check"
+version = "0.0.0"
+edition = "2021"
+rust-version = "1.88"
+publish = false
+
+[workspace]
+
+[features]
+sdk-msrv-pin = ["durable-workflow/msrv-1-86"]
+
+[dependencies]
+durable-workflow = { path = "../..", default-features = false }
+apache-avro = { version = "=0.22.0", default-features = false }
diff --git a/tests/native-composition/src/main.rs b/tests/native-composition/src/main.rs
new file mode 100644
index 0000000..37bff0a
--- /dev/null
+++ b/tests/native-composition/src/main.rs
@@ -0,0 +1,4 @@
+fn main() {
+    let _client = durable_workflow::Client::builder("http://127.0.0.1:8080");
+    let _schema = apache_avro::Schema::parse_str("\"null\"").unwrap();
+}

From 60d99e64e894aafb9b39db98d9acd6181b82f747 Mon Sep 17 00:00:00 2001
From: Richard McDaniel <1130888+rmcdaniel@users.noreply.github.com>
Date: Sat, 14 Nov 2026 11:54:19 +0000
Subject: [PATCH 3/3] Keep the positive composition lock free of the negative
 feature

---
 scripts/ci/check-native-composition.sh | 2 +-
 tests/native-composition/Cargo.toml    | 3 ---
 2 files changed, 1 insertion(+), 4 deletions(-)

diff --git a/scripts/ci/check-native-composition.sh b/scripts/ci/check-native-composition.sh
index 060d85e..6fe5103 100755
--- a/scripts/ci/check-native-composition.sh
+++ b/scripts/ci/check-native-composition.sh
@@ -11,7 +11,7 @@ cargo check --manifest-path "$composition_manifest"
 
 # Re-enabling the legacy compiler pin must retain the real resolver refusal.
 if cargo metadata --format-version 1 --manifest-path "$composition_manifest" \
-    --features sdk-msrv-pin >"$composition_log" 2>&1; then
+    --features durable-workflow/msrv-1-86 >"$composition_log" 2>&1; then
     printf 'native composition unexpectedly accepted the incompatible MSRV pin\n' >&2
     exit 1
 fi
diff --git a/tests/native-composition/Cargo.toml b/tests/native-composition/Cargo.toml
index 6a7e5fb..7218bc0 100644
--- a/tests/native-composition/Cargo.toml
+++ b/tests/native-composition/Cargo.toml
@@ -7,9 +7,6 @@ publish = false
 
 [workspace]
 
-[features]
-sdk-msrv-pin = ["durable-workflow/msrv-1-86"]
-
 [dependencies]
 durable-workflow = { path = "../..", default-features = false }
 apache-avro = { version = "=0.22.0", default-features = false }