diff --git a/.github/workflows/framework-resolution-check.yml b/.github/workflows/framework-resolution-check.yml
new file mode 100644
index 00000000..a74e5be8
--- /dev/null
+++ b/.github/workflows/framework-resolution-check.yml
@@ -0,0 +1,38 @@
+name: Framework resolution check
+
+# AAASM-4518 pre-publish guard: agent-assembly's runtime dependency floors must
+# stay co-installable with the supported agent frameworks (AutoGen / CrewAI /
+# Semantic Kernel). A floor raised above what a framework permits is a metadata-only
+# break that only surfaces AFTER the immutable wheel is published to PyPI — this job
+# turns that into a PR-time failure. See scripts/ci/check_framework_resolution.py.
+on:
+  pull_request:
+    paths:
+      - "pyproject.toml"
+      - "uv.lock"
+      - "scripts/ci/check_framework_resolution.py"
+      - ".github/workflows/framework-resolution-check.yml"
+  push:
+    branches: [master]
+    paths:
+      - "pyproject.toml"
+      - "uv.lock"
+      - "scripts/ci/check_framework_resolution.py"
+      - ".github/workflows/framework-resolution-check.yml"
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+permissions:
+  contents: read
+
+jobs:
+  framework-floors-resolve:
+    name: Dependency floors co-resolve with supported frameworks
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0  # v7
+      - uses: astral-sh/setup-uv@11f9893b081a58869d3b5fccaea48c9e9e46f990  # v7
+      - name: Resolve agent-assembly floors against the framework matrix
+        run: python scripts/ci/check_framework_resolution.py --python-version 3.12
diff --git a/pyproject.toml b/pyproject.toml
index 1a9b7012..cc7b0de0 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -24,28 +24,40 @@ classifiers = [
     "Programming Language :: Python :: 3.14",
 ]
 dependencies = [
-    "pydantic>=2.13.4,<3.0.0",
+    # AAASM-4518: floor held at the true minimum 2.0 — the SDK only uses
+    # BaseModel/Field/model_dump, all stable since pydantic 2.0. AAASM-4434 raised
+    # this to >=2.13.4 by pinning the floor to the then-resolved version, which made
+    # agent-assembly un-co-installable with CrewAI (caps pydantic<2.13) and Semantic
+    # Kernel (caps <2.12) — a framework-compat regression vs rc.3. Keep the floor at
+    # what the code needs, not what the lockfile happened to resolve to.
+    "pydantic>=2.0.0,<3.0.0",
     "httpx>=0.27.0,<1.0.0",
     "typing-extensions>=4.16.0",
     # AAASM-1654 (PR-E): OpControlSubscriber consumes PolicyService.OpControlStream
-    # via gRPC. Held to grpcio's modern stable line.
-    "grpcio>=1.82.1,<2",
-    # AAASM-4434 (dependency completeness re-audit): resolves to 6.33.6, not raw
-    # PyPI latest (7.35.1), even though >=5,<8 permitted 7.x. Confirmed this is a
-    # REAL transitive ceiling, not a stale "permissive floor" resolution: the
-    # `dev`/test group's pydantic-ai>=2.9.0 pulls in
-    # `pydantic-ai-slim[...,logfire,...]`, and logfire (<=4.37.0) pins
-    # `opentelemetry-exporter-otlp-proto-http<1.43.0`; every otlp-proto-http
-    # release in that range depends on an `opentelemetry-proto` that caps
-    # `protobuf<7.0`. Verified by temporarily setting `protobuf>=7.35.1,<8` and
-    # re-running `uv lock`, which fails with a resolver conflict rooted at
-    # pydantic-ai's logfire extra; a bare `uv lock --upgrade` (no floor change)
-    # also leaves protobuf pinned at 6.33.6. Re-audit once logfire raises its
-    # opentelemetry-exporter-otlp-proto-http ceiling above 1.43.0.
-    # AAASM-4434 (manifest transparency follow-up): floor tightened from the
-    # wide-open "5" to the exact resolved 6.33.6 so the manifest states what is
-    # actually locked, not just the outer bound of what's permitted.
-    "protobuf>=6.33.6,<8",
+    # via gRPC. AAASM-4518: floor restored to rc.3's >=1.66. AAASM-4434 raised it to
+    # >=1.82.1 to mirror the then-resolved version — an over-tighten, not a real
+    # minimum required by the SDK.
+    "grpcio>=1.66,<2",
+    # AAASM-4518: floor restored to rc.3's >=5 so agent-assembly can co-install with
+    # AutoGen (autogen-core>=0.7.5 caps protobuf<5.30). AAASM-4434 raised this to
+    # >=6.33.6 by pinning the floor to the then-resolved version, which made rc.4
+    # unresolvable with AutoGen — a framework-compat regression vs rc.3.
+    #
+    # CAVEAT (pre-existing, NOT introduced by this change): the checked-in gRPC stubs
+    # under agent_assembly/proto/ are protobuf gencode 6.31.1 and require a protobuf
+    # 6.x RUNTIME (>=6.31.1) to import — protobuf 5.x raises a VersionError. Those
+    # stubs are imported only by the optional OpControl gRPC transport
+    # (agent_assembly/op_control.py), never at package-import time, so mainstream
+    # framework quick-starts (which don't use that transport) run fine under protobuf
+    # 5.x — exactly as they did on rc.3, which also shipped 6.31.1 gencode under a
+    # >=5 floor since 2026-05-21. A user who needs the OpControl gRPC path must have
+    # protobuf>=6.31.1. Regenerating the stubs at 5.x gencode to make protobuf 5.x
+    # fully runtime-safe is a separate concern, not this compat fix.
+    #
+    # dev/test note: a bare `uv lock` still resolves protobuf to 6.33.6 because the
+    # dev-only pydantic-ai logfire extra caps protobuf<7.0 (via opentelemetry-proto);
+    # that transitive dev-time ceiling is independent of this runtime floor.
+    "protobuf>=5,<8",
 ]
 
 [project.optional-dependencies]
diff --git a/scripts/ci/check_framework_resolution.py b/scripts/ci/check_framework_resolution.py
new file mode 100644
index 00000000..272794af
--- /dev/null
+++ b/scripts/ci/check_framework_resolution.py
@@ -0,0 +1,137 @@
+#!/usr/bin/env python3
+"""Pre-publish guard: agent-assembly's dependency floors must co-resolve with the
+supported agent frameworks.
+
+WHY this exists (AAASM-4518): a well-meaning "pin the floor to the resolved
+version" bump (AAASM-4434) raised ``pydantic``/``protobuf`` floors above what
+CrewAI, Semantic Kernel, and AutoGen permit. Because the floors are metadata, the
+break only surfaced *after* the wheel was published to PyPI (rc.4 is immutable) —
+downstream users could no longer ``pip install agent-assembly`` alongside their
+framework. This guard turns that post-publish surprise into a PR-time failure.
+
+It resolves the SDK's *declared runtime floors* (read live from
+``[project.dependencies]``) together with each framework at its current release
+floor, using ``uv pip compile`` as an offline-metadata SAT solve. It never builds
+or imports agent-assembly, so it is fast and runs on any platform. A floor that
+excludes a framework's supported range makes the union unsatisfiable and fails the
+guard, naming the conflicting constraint.
+
+Usage::
+
+    python scripts/ci/check_framework_resolution.py            # check current tree
+    python scripts/ci/check_framework_resolution.py --python-version 3.12
+    python scripts/ci/check_framework_resolution.py --pyproject path/to/pyproject.toml
+
+Exit code 0 = every framework co-resolves; 1 = at least one conflict (details
+printed); 2 = harness error (uv missing, pyproject unreadable).
+"""
+
+from __future__ import annotations
+
+import argparse
+import subprocess
+import sys
+import tempfile
+import tomllib
+from pathlib import Path
+
+# The frameworks agent-assembly ships quick-start examples for, each pinned at the
+# CURRENT release floor. The floor matters: an unconstrained `framework` lets the
+# resolver pick an ancient version that trivially resolves, hiding the very conflict
+# we guard against. Bump these floors when a framework's supported release moves.
+# (Mirrors the frameworks called out in AAASM-4518 / examples#268.)
+FRAMEWORK_MATRIX: list[str] = [
+    "autogen-core>=0.7.5",  # caps protobuf<5.30
+    "crewai>=1.15.2",  # caps pydantic<2.13
+    "semantic-kernel>=1.30",  # caps pydantic<2.12
+]
+
+DEFAULT_PYTHON_VERSION = "3.12"  # the SDK's minimum supported interpreter
+
+
+def read_runtime_floors(pyproject: Path) -> list[str]:
+    """Return the ``[project.dependencies]`` specifiers verbatim from pyproject.toml."""
+    with pyproject.open("rb") as fh:
+        data = tomllib.load(fh)
+    deps = data.get("project", {}).get("dependencies")
+    if not deps:
+        raise SystemExit(f"error: no [project.dependencies] found in {pyproject}")
+    # Drop self-referential extras (e.g. `agent-assembly[runtime]`) — they are not
+    # third-party floors and would force a build of the local project.
+    return [d for d in deps if not d.replace(" ", "").startswith("agent-assembly")]
+
+
+def resolve(reqs: list[str], python_version: str) -> tuple[bool, str]:
+    """Try to resolve ``reqs`` together. Returns (ok, combined resolver output)."""
+    with tempfile.TemporaryDirectory() as tmp:
+        req_in = Path(tmp) / "req.in"
+        req_out = Path(tmp) / "req.txt"
+        req_in.write_text("\n".join(reqs) + "\n")
+        proc = subprocess.run(
+            [
+                "uv",
+                "pip",
+                "compile",
+                str(req_in),
+                "--python-version",
+                python_version,
+                "--output-file",
+                str(req_out),
+                "--quiet",
+                "--no-header",
+            ],
+            capture_output=True,
+            text=True,
+        )
+    return proc.returncode == 0, (proc.stderr + proc.stdout).strip()
+
+
+def main() -> int:
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument(
+        "--pyproject",
+        default=str(Path(__file__).resolve().parents[2] / "pyproject.toml"),
+        help="path to pyproject.toml (default: repo root)",
+    )
+    parser.add_argument(
+        "--python-version",
+        default=DEFAULT_PYTHON_VERSION,
+        help=f"target interpreter for resolution (default: {DEFAULT_PYTHON_VERSION})",
+    )
+    args = parser.parse_args()
+
+    try:
+        floors = read_runtime_floors(Path(args.pyproject))
+    except (OSError, tomllib.TOMLDecodeError) as exc:
+        print(f"error: cannot read {args.pyproject}: {exc}", file=sys.stderr)
+        return 2
+
+    print("agent-assembly runtime floors under test:")
+    for spec in floors:
+        print(f"  {spec}")
+    print(f"target python: {args.python_version}\n")
+
+    failures: list[tuple[str, str]] = []
+    for framework in FRAMEWORK_MATRIX:
+        ok, output = resolve(floors + [framework], args.python_version)
+        status = "OK  " if ok else "FAIL"
+        print(f"[{status}] agent-assembly floors + {framework}")
+        if not ok:
+            failures.append((framework, output))
+
+    if failures:
+        print("\nFramework resolution conflicts (a floor excludes a supported framework):")
+        for framework, output in failures:
+            print(f"\n--- {framework} ---\n{output}")
+        print(
+            "\nRelax the offending floor to the widest range the SDK actually "
+            "supports before publishing. See AAASM-4518."
+        )
+        return 1
+
+    print("\nAll frameworks co-resolve with the current dependency floors.")
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())
diff --git a/uv.lock b/uv.lock
index c29432db..5626737d 100644
--- a/uv.lock
+++ b/uv.lock
@@ -92,10 +92,10 @@ test = [
 [package.metadata]
 requires-dist = [
     { name = "agent-assembly", extras = ["runtime"], marker = "extra == 'all'" },
-    { name = "grpcio", specifier = ">=1.82.1,<2" },
+    { name = "grpcio", specifier = ">=1.66,<2" },
     { name = "httpx", specifier = ">=0.27.0,<1.0.0" },
-    { name = "protobuf", specifier = ">=6.33.6,<8" },
-    { name = "pydantic", specifier = ">=2.13.4,<3.0.0" },
+    { name = "protobuf", specifier = ">=5,<8" },
+    { name = "pydantic", specifier = ">=2.0.0,<3.0.0" },
     { name = "typing-extensions", specifier = ">=4.16.0" },
 ]
 provides-extras = ["runtime", "all"]