diff --git a/backend/routers/v1/social_proxy.py b/backend/routers/v1/social_proxy.py
new file mode 100644
index 00000000..d0578a45
--- /dev/null
+++ b/backend/routers/v1/social_proxy.py
@@ -0,0 +1,182 @@
+from __future__ import annotations
+
+import json
+from datetime import datetime, timezone
+from typing import Optional
+from urllib.parse import urlencode
+
+from fastapi import APIRouter, Depends, HTTPException, Query
+from fastapi.responses import RedirectResponse
+from loguru import logger
+from sqlalchemy import text
+from sqlalchemy.orm import Session
+
+from services.database import get_db
+
+router = APIRouter(prefix="/v1/social-proxy", tags=["social-proxy"])
+
+
+def _utc_now_iso() -> str:
+    return datetime.now(timezone.utc).isoformat()
+
+
+def _ensure_tables(db: Session) -> None:
+    # Keep this router backward-compatible on tenant DBs without migrations.
+    db.execute(text("""
+        CREATE TABLE IF NOT EXISTS oauth_nonce_sessions (
+            id INTEGER PRIMARY KEY AUTOINCREMENT,
+            state TEXT NOT NULL UNIQUE,
+            nonce TEXT NOT NULL,
+            user_id TEXT NOT NULL,
+            platform TEXT NOT NULL,
+            channel_id INTEGER,
+            consumed_at TEXT,
+            expires_at TEXT,
+            created_at TEXT NOT NULL
+        )
+    """))
+    db.execute(text("""
+        CREATE TABLE IF NOT EXISTS social_channels (
+            id INTEGER PRIMARY KEY AUTOINCREMENT,
+            user_id TEXT NOT NULL,
+            platform TEXT NOT NULL,
+            platform_account_id TEXT NOT NULL,
+            token_bundle TEXT NOT NULL,
+            token_version INTEGER NOT NULL DEFAULT 1,
+            publication_linkage TEXT,
+            is_connected INTEGER NOT NULL DEFAULT 1,
+            created_at TEXT NOT NULL,
+            updated_at TEXT NOT NULL,
+            UNIQUE(platform, platform_account_id)
+        )
+    """))
+
+
+def _build_redirect(base_url: str, code: str, message: str, channel_id: Optional[int] = None) -> RedirectResponse:
+    params = {"code": code, "message": message}
+    if channel_id is not None:
+        params["channel_id"] = str(channel_id)
+    return RedirectResponse(url=f"{base_url}?{urlencode(params)}", status_code=303)
+
+
+@router.get("/oauth/callback")
+def oauth_callback(
+    state: str = Query(...),
+    platform: str = Query(...),
+    account_id: str = Query(...),
+    token_bundle: str = Query(..., description="Serialized token payload"),
+    ui_redirect: str = Query("/dashboard/connections"),
+    db: Session = Depends(get_db),
+):
+    """Consume OAuth callback, bind to user/platform, and upsert social channel connection."""
+    _ensure_tables(db)
+
+    record = db.execute(
+        text("""
+            SELECT id, nonce, user_id, platform, channel_id, consumed_at, expires_at
+            FROM oauth_nonce_sessions WHERE state = :state
+        """),
+        {"state": state},
+    ).mappings().first()
+
+    if not record:
+        return _build_redirect(ui_redirect, "invalid_state", "Missing OAuth session")
+
+    if record["consumed_at"] is not None:
+        return _build_redirect(ui_redirect, "state_reused", "OAuth state already consumed")
+
+    if record["platform"] != platform:
+        return _build_redirect(ui_redirect, "platform_mismatch", "Platform mismatch")
+
+    if record["expires_at"] and record["expires_at"] < _utc_now_iso():
+        return _build_redirect(ui_redirect, "state_expired", "OAuth session expired")
+
+    user_id = record["user_id"]
+
+    # Validate token payload is JSON.
+    try:
+        parsed_bundle = json.loads(token_bundle)
+    except json.JSONDecodeError as exc:
+        raise HTTPException(status_code=400, detail="Invalid token_bundle JSON") from exc
+
+    now = _utc_now_iso()
+
+    existing = db.execute(
+        text("""
+            SELECT id, publication_linkage, token_version
+            FROM social_channels
+            WHERE platform = :platform AND platform_account_id = :account_id
+        """),
+        {"platform": platform, "account_id": account_id},
+    ).mappings().first()
+
+    if existing:
+        # Reconnect path: preserve publication linkage and bump token version.
+        db.execute(
+            text("""
+                UPDATE social_channels
+                SET user_id = :user_id,
+                    token_bundle = :token_bundle,
+                    token_version = :token_version,
+                    is_connected = 1,
+                    updated_at = :updated_at
+                WHERE id = :id
+            """),
+            {
+                "id": existing["id"],
+                "user_id": user_id,
+                "token_bundle": json.dumps(parsed_bundle),
+                "token_version": int(existing["token_version"] or 0) + 1,
+                "updated_at": now,
+            },
+        )
+        channel_id = existing["id"]
+        result_code = "reconnected"
+        result_message = "Channel reconnected"
+    else:
+        db.execute(
+            text("""
+                INSERT INTO social_channels (
+                    user_id, platform, platform_account_id, token_bundle,
+                    token_version, publication_linkage, is_connected, created_at, updated_at
+                ) VALUES (
+                    :user_id, :platform, :account_id, :token_bundle,
+                    1, :publication_linkage, 1, :created_at, :updated_at
+                )
+            """),
+            {
+                "user_id": user_id,
+                "platform": platform,
+                "account_id": account_id,
+                "token_bundle": json.dumps(parsed_bundle),
+                "publication_linkage": None,
+                "created_at": now,
+                "updated_at": now,
+            },
+        )
+        channel_id = db.execute(text("SELECT last_insert_rowid()")).scalar_one()
+        result_code = "connected"
+        result_message = "Channel connected"
+
+    # Bind callback session to concrete channel/user/platform and mark consumed.
+    db.execute(
+        text("""
+            UPDATE oauth_nonce_sessions
+            SET consumed_at = :consumed_at,
+                channel_id = :channel_id,
+                user_id = :user_id,
+                platform = :platform
+            WHERE id = :id
+        """),
+        {
+            "id": record["id"],
+            "consumed_at": now,
+            "channel_id": channel_id,
+            "user_id": user_id,
+            "platform": platform,
+        },
+    )
+
+    db.commit()
+    logger.info(f"OAuth callback complete user={user_id} platform={platform} channel_id={channel_id}")
+    return _build_redirect(ui_redirect, result_code, result_message, channel_id)