feat: add upload_attachment MCP tool

Add support for uploading file attachments to Grist documents:

- GristClient.upload_attachment() method using multipart/form-data
- upload_attachment tool function with base64 decoding and MIME detection
- Tool registration in server.py
- Comprehensive unit tests (7 new tests)

Returns attachment ID for linking to records via update_records.

Bumps version to 1.3.0.

.github/workflows/build.yaml

@@ -18,7 +18,7 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v4
+        uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6
 
       - name: Log in to Container Registry
         uses: docker/login-action@v3

CHANGELOG.md

@@ -5,6 +5,43 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [1.3.0] - 2026-01-03
+
+### Added
+
+#### Attachment Upload
+- **`upload_attachment` MCP tool**: Upload files to Grist documents
+- Base64-encoded content input (required for JSON-based MCP protocol)
+- Automatic MIME type detection from filename
+- Returns attachment ID for linking to records via `update_records`
+
+#### Usage
+```python
+# 1. Upload attachment
+result = upload_attachment(
+    document="accounting",
+    filename="invoice.pdf",
+    content_base64="JVBERi0xLjQK..."
+)
+# Returns: {"attachment_id": 42, "filename": "invoice.pdf", "size_bytes": 31395}
+
+# 2. Link to record
+update_records(document="accounting", table="Bills", records=[
+    {"id": 1, "fields": {"Attachment": [42]}}
+])
+```
+
+## [1.2.0] - 2026-01-02
+
+### Added
+
+#### Session Token Proxy
+- **Session token proxy**: Agents can request short-lived tokens for bulk operations
+- `get_proxy_documentation` MCP tool: returns complete proxy API spec
+- `request_session_token` MCP tool: creates scoped session tokens with TTL (max 1 hour)
+- `POST /api/v1/proxy` HTTP endpoint: accepts session tokens for direct API access
+- Supports all 11 Grist operations (read, write, schema) via HTTP
+
 ## [1.1.0] - 2026-01-02
 
 ### Added

README.md

@@ -150,6 +150,7 @@ Add to your MCP client configuration (e.g., Claude Desktop):
 | `GRIST_MCP_TOKEN` | Agent authentication token (required) | - |
 | `CONFIG_PATH` | Path to config file inside container | `/app/config.yaml` |
 | `LOG_LEVEL` | Logging verbosity (`DEBUG`, `INFO`, `WARNING`, `ERROR`) | `INFO` |
+| `GRIST_MCP_URL` | Public URL of this server (for session proxy tokens) | - |
 
 ### config.yaml Structure
 

docs/plans/2026-01-03-attachment-upload-design.md

@@ -0,0 +1,187 @@
+# Attachment Upload Feature Design
+
+**Date:** 2026-01-03
+**Status:** Approved
+
+## Summary
+
+Add an `upload_attachment` MCP tool to upload files to Grist documents and receive an attachment ID for linking to records.
+
+## Design Decisions
+
+| Decision | Choice | Rationale |
+|----------|--------|-----------|
+| Content encoding | Base64 string | MCP tools use JSON; binary must be encoded |
+| Batch support | Single file only | YAGNI; caller can loop if needed |
+| Linking behavior | Upload only, return ID | Single responsibility; use existing `update_records` to link |
+| Download support | Not included | YAGNI; can add later if needed |
+| Permission level | Write | Attachments are data, not schema |
+| Proxy support | MCP tool only | Reduces scope; scripts can use Grist API directly |
+
+## Tool Interface
+
+### Input Schema
+
+```json
+{
+  "type": "object",
+  "properties": {
+    "document": {
+      "type": "string",
+      "description": "Document name"
+    },
+    "filename": {
+      "type": "string",
+      "description": "Filename with extension (e.g., 'invoice.pdf')"
+    },
+    "content_base64": {
+      "type": "string",
+      "description": "File content as base64-encoded string"
+    },
+    "content_type": {
+      "type": "string",
+      "description": "MIME type (optional, auto-detected from filename if omitted)"
+    }
+  },
+  "required": ["document", "filename", "content_base64"]
+}
+```
+
+### Response
+
+```json
+{
+  "attachment_id": 42,
+  "filename": "invoice.pdf",
+  "size_bytes": 30720
+}
+```
+
+### Usage Example
+
+```python
+# 1. Upload attachment
+result = upload_attachment(
+    document="accounting",
+    filename="Invoice-001.pdf",
+    content_base64="JVBERi0xLjQK..."
+)
+
+# 2. Link to record via existing update_records tool
+update_records("Bills", [{
+    "id": 1,
+    "fields": {"Attachment": [result["attachment_id"]]}
+}])
+```
+
+## Implementation
+
+### Files to Modify
+
+1. **`src/grist_mcp/grist_client.py`** - Add `upload_attachment()` method
+2. **`src/grist_mcp/tools/write.py`** - Add tool function
+3. **`src/grist_mcp/server.py`** - Register tool
+
+### GristClient Method
+
+```python
+async def upload_attachment(
+    self,
+    filename: str,
+    content: bytes,
+    content_type: str | None = None
+) -> dict:
+    """Upload a file attachment. Returns attachment metadata."""
+    if content_type is None:
+        content_type = "application/octet-stream"
+
+    files = {"upload": (filename, content, content_type)}
+
+    async with httpx.AsyncClient(timeout=self._timeout) as client:
+        response = await client.post(
+            f"{self._base_url}/attachments",
+            headers=self._headers,
+            files=files,
+        )
+        response.raise_for_status()
+        # Grist returns list of attachment IDs
+        attachment_ids = response.json()
+        return {
+            "attachment_id": attachment_ids[0],
+            "filename": filename,
+            "size_bytes": len(content),
+        }
+```
+
+### Tool Function
+
+```python
+import base64
+import mimetypes
+
+async def upload_attachment(
+    agent: Agent,
+    auth: Authenticator,
+    document: str,
+    filename: str,
+    content_base64: str,
+    content_type: str | None = None,
+    client: GristClient | None = None,
+) -> dict:
+    """Upload a file attachment to a document."""
+    auth.authorize(agent, document, Permission.WRITE)
+
+    # Decode base64
+    try:
+        content = base64.b64decode(content_base64)
+    except Exception:
+        raise ValueError("Invalid base64 encoding")
+
+    # Auto-detect MIME type if not provided
+    if content_type is None:
+        content_type, _ = mimetypes.guess_type(filename)
+        if content_type is None:
+            content_type = "application/octet-stream"
+
+    if client is None:
+        doc = auth.get_document(document)
+        client = GristClient(doc)
+
+    return await client.upload_attachment(filename, content, content_type)
+```
+
+## Error Handling
+
+| Error | Cause | Response |
+|-------|-------|----------|
+| Invalid base64 | Malformed content_base64 | `ValueError: Invalid base64 encoding` |
+| Authorization | Agent lacks write permission | `AuthError` (existing pattern) |
+| Grist API error | Upload fails | `httpx.HTTPStatusError` (existing pattern) |
+
+## Testing
+
+### Unit Tests
+
+**`tests/unit/test_tools_write.py`:**
+- `test_upload_attachment_success` - Valid base64, returns attachment_id
+- `test_upload_attachment_invalid_base64` - Raises ValueError
+- `test_upload_attachment_auth_required` - Verifies write permission check
+- `test_upload_attachment_mime_detection` - Auto-detects type from filename
+
+**`tests/unit/test_grist_client.py`:**
+- `test_upload_attachment_api_call` - Correct multipart request format
+- `test_upload_attachment_with_explicit_content_type` - Passes through MIME type
+
+### Mock Approach
+
+Mock `httpx.AsyncClient` responses; no Grist server needed for unit tests.
+
+## Future Considerations
+
+Not included in this implementation (YAGNI):
+- Batch upload (multiple files)
+- Download attachment
+- Proxy API support
+- Size limit validation (rely on Grist's limits)
+
+These can be added if real use cases emerge.

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "grist-mcp"
-version = "1.1.0"
+version = "1.3.0"
 description = "MCP server for AI agents to interact with Grist documents"
 requires-python = ">=3.14"
 dependencies = [
@@ -28,3 +28,6 @@ build-backend = "hatchling.build"
 [tool.pytest.ini_options]
 asyncio_mode = "auto"
 testpaths = ["tests/unit", "tests/integration"]
+markers = [
+    "integration: marks tests as integration tests (require Docker containers)",
+]

src/grist_mcp/grist_client.py

@@ -116,6 +116,39 @@ class GristClient:
         """Delete records by ID."""
         await self._request("POST", f"/tables/{table}/data/delete", json=record_ids)
 
+    async def upload_attachment(
+        self,
+        filename: str,
+        content: bytes,
+        content_type: str = "application/octet-stream",
+    ) -> dict:
+        """Upload a file attachment. Returns attachment metadata.
+
+        Args:
+            filename: Name for the uploaded file.
+            content: File content as bytes.
+            content_type: MIME type of the file.
+
+        Returns:
+            Dict with attachment_id, filename, and size_bytes.
+        """
+        files = {"upload": (filename, content, content_type)}
+
+        async with httpx.AsyncClient(timeout=self._timeout) as client:
+            response = await client.post(
+                f"{self._base_url}/attachments",
+                headers=self._headers,
+                files=files,
+            )
+            response.raise_for_status()
+            # Grist returns list of attachment IDs
+            attachment_ids = response.json()
+            return {
+                "attachment_id": attachment_ids[0],
+                "filename": filename,
+                "size_bytes": len(content),
+            }
+
     # Schema operations
 
     async def create_table(self, table_id: str, columns: list[dict]) -> str:

src/grist_mcp/main.py

@@ -12,6 +12,8 @@ from mcp.server.sse import SseServerTransport
 from grist_mcp.server import create_server
 from grist_mcp.config import Config, load_config
 from grist_mcp.auth import Authenticator, AuthError
+from grist_mcp.session import SessionTokenManager
+from grist_mcp.proxy import parse_proxy_request, dispatch_proxy_request, ProxyError
 from grist_mcp.logging import setup_logging
 
 
@@ -43,6 +45,20 @@ async def send_error(send: Send, status: int, message: str) -> None:
     })
 
 
+async def send_json_response(send: Send, status: int, data: dict) -> None:
+    """Send a JSON response."""
+    body = json.dumps(data).encode()
+    await send({
+        "type": "http.response.start",
+        "status": status,
+        "headers": [[b"content-type", b"application/json"]],
+    })
+    await send({
+        "type": "http.response.body",
+        "body": body,
+    })
+
+
 CONFIG_TEMPLATE = """\
 # grist-mcp configuration
 #
@@ -110,6 +126,8 @@ def _ensure_config(config_path: str) -> bool:
 def create_app(config: Config):
     """Create the ASGI application."""
     auth = Authenticator(config)
+    token_manager = SessionTokenManager()
+    proxy_base_url = os.environ.get("GRIST_MCP_URL")
 
     sse = SseServerTransport("/messages")
 
@@ -127,7 +145,7 @@ def create_app(config: Config):
             return
 
         # Create a server instance for this authenticated connection
-        server = create_server(auth, agent)
+        server = create_server(auth, agent, token_manager, proxy_base_url)
 
         async with sse.connect_sse(scope, receive, send) as streams:
             await server.run(
@@ -159,6 +177,58 @@ def create_app(config: Config):
             "body": b'{"error":"Not found"}',
         })
 
+    async def handle_proxy(scope: Scope, receive: Receive, send: Send) -> None:
+        # Extract token
+        token = _get_bearer_token(scope)
+        if not token:
+            await send_json_response(send, 401, {
+                "success": False,
+                "error": "Missing Authorization header",
+                "code": "INVALID_TOKEN",
+            })
+            return
+
+        # Validate session token
+        session = token_manager.validate_token(token)
+        if session is None:
+            await send_json_response(send, 401, {
+                "success": False,
+                "error": "Invalid or expired token",
+                "code": "TOKEN_EXPIRED",
+            })
+            return
+
+        # Read request body
+        body = b""
+        while True:
+            message = await receive()
+            body += message.get("body", b"")
+            if not message.get("more_body", False):
+                break
+
+        try:
+            request_data = json.loads(body)
+        except json.JSONDecodeError:
+            await send_json_response(send, 400, {
+                "success": False,
+                "error": "Invalid JSON",
+                "code": "INVALID_REQUEST",
+            })
+            return
+
+        # Parse and dispatch
+        try:
+            request = parse_proxy_request(request_data)
+            result = await dispatch_proxy_request(request, session, auth)
+            await send_json_response(send, 200, result)
+        except ProxyError as e:
+            status = 403 if e.code == "UNAUTHORIZED" else 400
+            await send_json_response(send, status, {
+                "success": False,
+                "error": e.message,
+                "code": e.code,
+            })
+
     async def app(scope: Scope, receive: Receive, send: Send) -> None:
         if scope["type"] != "http":
             return
@@ -172,6 +242,8 @@ def create_app(config: Config):
             await handle_sse(scope, receive, send)
         elif path == "/messages" and method == "POST":
             await handle_messages(scope, receive, send)
+        elif path == "/api/v1/proxy" and method == "POST":
+            await handle_proxy(scope, receive, send)
         else:
             await handle_not_found(scope, receive, send)
 
@@ -180,11 +252,18 @@ def create_app(config: Config):
 
 def _print_mcp_config(external_port: int, tokens: list) -> None:
     """Print Claude Code MCP configuration."""
+    # Use GRIST_MCP_URL if set, otherwise fall back to localhost
+    base_url = os.environ.get("GRIST_MCP_URL")
+    if base_url:
+        sse_url = f"{base_url.rstrip('/')}/sse"
+    else:
+        sse_url = f"http://localhost:{external_port}/sse"
+
     print()
     print("Claude Code MCP configuration (copy-paste to add):")
     for t in tokens:
         config = (
-            f'{{"type": "sse", "url": "http://localhost:{external_port}/sse", '
+            f'{{"type": "sse", "url": "{sse_url}", '
             f'"headers": {{"Authorization": "Bearer {t.token}"}}}}'
         )
         print(f"  claude mcp add-json grist-{t.name} '{config}'")

src/grist_mcp/proxy.py

@@ -0,0 +1,192 @@
+"""HTTP proxy handler for session token access."""
+
+from dataclasses import dataclass
+from typing import Any
+
+from grist_mcp.auth import Authenticator
+from grist_mcp.grist_client import GristClient
+from grist_mcp.session import SessionToken
+
+
+class ProxyError(Exception):
+    """Error during proxy request processing."""
+
+    def __init__(self, message: str, code: str):
+        self.message = message
+        self.code = code
+        super().__init__(message)
+
+
+@dataclass
+class ProxyRequest:
+    """Parsed proxy request."""
+    method: str
+    table: str | None = None
+    records: list[dict] | None = None
+    record_ids: list[int] | None = None
+    filter: dict | None = None
+    sort: str | None = None
+    limit: int | None = None
+    query: str | None = None
+    table_id: str | None = None
+    columns: list[dict] | None = None
+    column_id: str | None = None
+    column_type: str | None = None
+    formula: str | None = None
+    type: str | None = None
+
+
+METHODS_REQUIRING_TABLE = {
+    "get_records", "describe_table", "add_records", "update_records",
+    "delete_records", "add_column", "modify_column", "delete_column",
+}
+
+
+def parse_proxy_request(body: dict[str, Any]) -> ProxyRequest:
+    """Parse and validate a proxy request body."""
+    if "method" not in body:
+        raise ProxyError("Missing required field: method", "INVALID_REQUEST")
+
+    method = body["method"]
+
+    if method in METHODS_REQUIRING_TABLE and "table" not in body:
+        raise ProxyError(f"Missing required field 'table' for method '{method}'", "INVALID_REQUEST")
+
+    return ProxyRequest(
+        method=method,
+        table=body.get("table"),
+        records=body.get("records"),
+        record_ids=body.get("record_ids"),
+        filter=body.get("filter"),
+        sort=body.get("sort"),
+        limit=body.get("limit"),
+        query=body.get("query"),
+        table_id=body.get("table_id"),
+        columns=body.get("columns"),
+        column_id=body.get("column_id"),
+        column_type=body.get("column_type"),
+        formula=body.get("formula"),
+        type=body.get("type"),
+    )
+
+
+# Map methods to required permissions
+METHOD_PERMISSIONS = {
+    "list_tables": "read",
+    "describe_table": "read",
+    "get_records": "read",
+    "sql_query": "read",
+    "add_records": "write",
+    "update_records": "write",
+    "delete_records": "write",
+    "create_table": "schema",
+    "add_column": "schema",
+    "modify_column": "schema",
+    "delete_column": "schema",
+}
+
+
+async def dispatch_proxy_request(
+    request: ProxyRequest,
+    session: SessionToken,
+    auth: Authenticator,
+    client: GristClient | None = None,
+) -> dict[str, Any]:
+    """Dispatch a proxy request to the appropriate handler."""
+    # Check permission
+    required_perm = METHOD_PERMISSIONS.get(request.method)
+    if required_perm is None:
+        raise ProxyError(f"Unknown method: {request.method}", "INVALID_REQUEST")
+
+    if required_perm not in session.permissions:
+        raise ProxyError(
+            f"Permission '{required_perm}' required for {request.method}",
+            "UNAUTHORIZED",
+        )
+
+    # Create client if not provided
+    if client is None:
+        doc = auth.get_document(session.document)
+        client = GristClient(doc)
+
+    # Dispatch to appropriate method
+    try:
+        if request.method == "list_tables":
+            data = await client.list_tables()
+            return {"success": True, "data": {"tables": data}}
+
+        elif request.method == "describe_table":
+            data = await client.describe_table(request.table)
+            return {"success": True, "data": {"table": request.table, "columns": data}}
+
+        elif request.method == "get_records":
+            data = await client.get_records(
+                request.table,
+                filter=request.filter,
+                sort=request.sort,
+                limit=request.limit,
+            )
+            return {"success": True, "data": {"records": data}}
+
+        elif request.method == "sql_query":
+            if request.query is None:
+                raise ProxyError("Missing required field: query", "INVALID_REQUEST")
+            data = await client.sql_query(request.query)
+            return {"success": True, "data": {"records": data}}
+
+        elif request.method == "add_records":
+            if request.records is None:
+                raise ProxyError("Missing required field: records", "INVALID_REQUEST")
+            data = await client.add_records(request.table, request.records)
+            return {"success": True, "data": {"record_ids": data}}
+
+        elif request.method == "update_records":
+            if request.records is None:
+                raise ProxyError("Missing required field: records", "INVALID_REQUEST")
+            await client.update_records(request.table, request.records)
+            return {"success": True, "data": {"updated": len(request.records)}}
+
+        elif request.method == "delete_records":
+            if request.record_ids is None:
+                raise ProxyError("Missing required field: record_ids", "INVALID_REQUEST")
+            await client.delete_records(request.table, request.record_ids)
+            return {"success": True, "data": {"deleted": len(request.record_ids)}}
+
+        elif request.method == "create_table":
+            if request.table_id is None or request.columns is None:
+                raise ProxyError("Missing required fields: table_id, columns", "INVALID_REQUEST")
+            data = await client.create_table(request.table_id, request.columns)
+            return {"success": True, "data": {"table_id": data}}
+
+        elif request.method == "add_column":
+            if request.column_id is None or request.column_type is None:
+                raise ProxyError("Missing required fields: column_id, column_type", "INVALID_REQUEST")
+            await client.add_column(
+                request.table, request.column_id, request.column_type,
+                formula=request.formula,
+            )
+            return {"success": True, "data": {"column_id": request.column_id}}
+
+        elif request.method == "modify_column":
+            if request.column_id is None:
+                raise ProxyError("Missing required field: column_id", "INVALID_REQUEST")
+            await client.modify_column(
+                request.table, request.column_id,
+                type=request.type,
+                formula=request.formula,
+            )
+            return {"success": True, "data": {"column_id": request.column_id}}
+
+        elif request.method == "delete_column":
+            if request.column_id is None:
+                raise ProxyError("Missing required field: column_id", "INVALID_REQUEST")
+            await client.delete_column(request.table, request.column_id)
+            return {"success": True, "data": {"deleted": request.column_id}}
+
+        else:
+            raise ProxyError(f"Unknown method: {request.method}", "INVALID_REQUEST")
+
+    except ProxyError:
+        raise
+    except Exception as e:
+        raise ProxyError(str(e), "GRIST_ERROR")

src/grist_mcp/server.py

@@ -7,6 +7,9 @@ from mcp.server import Server
 from mcp.types import Tool, TextContent
 
 from grist_mcp.auth import Authenticator, Agent, AuthError
+from grist_mcp.session import SessionTokenManager
+from grist_mcp.tools.session import get_proxy_documentation as _get_proxy_documentation
+from grist_mcp.tools.session import request_session_token as _request_session_token
 from grist_mcp.logging import get_logger, extract_stats, format_tool_log
 
 logger = get_logger("server")
@@ -19,24 +22,33 @@ from grist_mcp.tools.read import sql_query as _sql_query
 from grist_mcp.tools.write import add_records as _add_records
 from grist_mcp.tools.write import update_records as _update_records
 from grist_mcp.tools.write import delete_records as _delete_records
+from grist_mcp.tools.write import upload_attachment as _upload_attachment
 from grist_mcp.tools.schema import create_table as _create_table
 from grist_mcp.tools.schema import add_column as _add_column
 from grist_mcp.tools.schema import modify_column as _modify_column
 from grist_mcp.tools.schema import delete_column as _delete_column
 
 
-def create_server(auth: Authenticator, agent: Agent) -> Server:
+def create_server(
+    auth: Authenticator,
+    agent: Agent,
+    token_manager: SessionTokenManager | None = None,
+    proxy_base_url: str | None = None,
+) -> Server:
     """Create and configure the MCP server for an authenticated agent.
 
     Args:
         auth: Authenticator instance for permission checks.
         agent: The authenticated agent for this server instance.
+        token_manager: Optional session token manager for HTTP proxy access.
+        proxy_base_url: Base URL for the proxy endpoint (e.g., "https://example.com").
 
     Returns:
         Configured MCP Server instance.
     """
     server = Server("grist-mcp")
     _current_agent = agent
+    _proxy_base_url = proxy_base_url
 
     @server.list_tools()
     async def list_tools() -> list[Tool]:
@@ -207,6 +219,60 @@ def create_server(auth: Authenticator, agent: Agent) -> Server:
                     "required": ["document", "table", "column_id"],
                 },
             ),
+            Tool(
+                name="upload_attachment",
+                description="Upload a file attachment to a Grist document. Returns attachment ID for linking to records via update_records.",
+                inputSchema={
+                    "type": "object",
+                    "properties": {
+                        "document": {
+                            "type": "string",
+                            "description": "Document name",
+                        },
+                        "filename": {
+                            "type": "string",
+                            "description": "Filename with extension (e.g., 'invoice.pdf')",
+                        },
+                        "content_base64": {
+                            "type": "string",
+                            "description": "File content as base64-encoded string",
+                        },
+                        "content_type": {
+                            "type": "string",
+                            "description": "MIME type (optional, auto-detected from filename)",
+                        },
+                    },
+                    "required": ["document", "filename", "content_base64"],
+                },
+            ),
+            Tool(
+                name="get_proxy_documentation",
+                description="Get complete documentation for the HTTP proxy API",
+                inputSchema={"type": "object", "properties": {}, "required": []},
+            ),
+            Tool(
+                name="request_session_token",
+                description="Request a short-lived token for direct HTTP API access. Use this to delegate bulk data operations to scripts.",
+                inputSchema={
+                    "type": "object",
+                    "properties": {
+                        "document": {
+                            "type": "string",
+                            "description": "Document name to grant access to",
+                        },
+                        "permissions": {
+                            "type": "array",
+                            "items": {"type": "string", "enum": ["read", "write", "schema"]},
+                            "description": "Permission levels to grant",
+                        },
+                        "ttl_seconds": {
+                            "type": "integer",
+                            "description": "Token lifetime in seconds (max 3600, default 300)",
+                        },
+                    },
+                    "required": ["document", "permissions"],
+                },
+            ),
         ]
 
     @server.call_tool()
@@ -285,6 +351,24 @@ def create_server(auth: Authenticator, agent: Agent) -> Server:
                     _current_agent, auth, arguments["document"], arguments["table"],
                     arguments["column_id"],
                 )
+            elif name == "upload_attachment":
+                result = await _upload_attachment(
+                    _current_agent, auth, arguments["document"],
+                    arguments["filename"], arguments["content_base64"],
+                    content_type=arguments.get("content_type"),
+                )
+            elif name == "get_proxy_documentation":
+                result = await _get_proxy_documentation()
+            elif name == "request_session_token":
+                if token_manager is None:
+                    return [TextContent(type="text", text="Session tokens not enabled")]
+                result = await _request_session_token(
+                    _current_agent, auth, token_manager,
+                    arguments["document"],
+                    arguments["permissions"],
+                    ttl_seconds=arguments.get("ttl_seconds", 300),
+                    proxy_base_url=_proxy_base_url,
+                )
             else:
                 return [TextContent(type="text", text=f"Unknown tool: {name}")]
 

src/grist_mcp/session.py

@@ -0,0 +1,73 @@
+"""Session token management for HTTP proxy access."""
+
+import secrets
+from dataclasses import dataclass
+from datetime import datetime, timedelta, timezone
+
+MAX_TTL_SECONDS = 3600  # 1 hour
+DEFAULT_TTL_SECONDS = 300  # 5 minutes
+
+
+@dataclass
+class SessionToken:
+    """A short-lived session token for proxy access."""
+    token: str
+    document: str
+    permissions: list[str]
+    agent_name: str
+    created_at: datetime
+    expires_at: datetime
+
+
+class SessionTokenManager:
+    """Manages creation and validation of session tokens."""
+
+    def __init__(self):
+        self._tokens: dict[str, SessionToken] = {}
+
+    def create_token(
+        self,
+        agent_name: str,
+        document: str,
+        permissions: list[str],
+        ttl_seconds: int = DEFAULT_TTL_SECONDS,
+    ) -> SessionToken:
+        """Create a new session token.
+
+        TTL is capped at MAX_TTL_SECONDS (1 hour).
+        """
+        now = datetime.now(timezone.utc)
+        token_str = f"sess_{secrets.token_urlsafe(32)}"
+
+        # Cap TTL at maximum
+        effective_ttl = min(ttl_seconds, MAX_TTL_SECONDS)
+
+        session = SessionToken(
+            token=token_str,
+            document=document,
+            permissions=permissions,
+            agent_name=agent_name,
+            created_at=now,
+            expires_at=now + timedelta(seconds=effective_ttl),
+        )
+
+        self._tokens[token_str] = session
+        return session
+
+    def validate_token(self, token: str) -> SessionToken | None:
+        """Validate a session token.
+
+        Returns the SessionToken if valid and not expired, None otherwise.
+        Also removes expired tokens lazily.
+        """
+        session = self._tokens.get(token)
+        if session is None:
+            return None
+
+        now = datetime.now(timezone.utc)
+        if session.expires_at < now:
+            # Token expired, remove it
+            del self._tokens[token]
+            return None
+
+        return session

src/grist_mcp/tools/session.py

@@ -0,0 +1,158 @@
+"""Session token tools for HTTP proxy access."""
+
+from grist_mcp.auth import Agent, Authenticator, AuthError, Permission
+from grist_mcp.session import SessionTokenManager
+
+
+PROXY_DOCUMENTATION = {
+    "description": "HTTP proxy API for bulk data operations. Use request_session_token to get a short-lived token, then call the proxy endpoint directly from scripts.",
+    "endpoint": "POST /api/v1/proxy",
+    "endpoint_note": "The full URL is returned in the 'proxy_url' field of request_session_token response",
+    "authentication": "Bearer token in Authorization header",
+    "request_format": {
+        "method": "Operation name (required)",
+        "table": "Table name (required for most operations)",
+    },
+    "methods": {
+        "get_records": {
+            "description": "Fetch records from a table",
+            "fields": {
+                "table": "string",
+                "filter": "object (optional)",
+                "sort": "string (optional)",
+                "limit": "integer (optional)",
+            },
+        },
+        "sql_query": {
+            "description": "Run a read-only SQL query",
+            "fields": {"query": "string"},
+        },
+        "list_tables": {
+            "description": "List all tables in the document",
+            "fields": {},
+        },
+        "describe_table": {
+            "description": "Get column information for a table",
+            "fields": {"table": "string"},
+        },
+        "add_records": {
+            "description": "Add records to a table",
+            "fields": {"table": "string", "records": "array of objects"},
+        },
+        "update_records": {
+            "description": "Update existing records",
+            "fields": {"table": "string", "records": "array of {id, fields}"},
+        },
+        "delete_records": {
+            "description": "Delete records by ID",
+            "fields": {"table": "string", "record_ids": "array of integers"},
+        },
+        "create_table": {
+            "description": "Create a new table",
+            "fields": {"table_id": "string", "columns": "array of {id, type}"},
+        },
+        "add_column": {
+            "description": "Add a column to a table",
+            "fields": {
+                "table": "string",
+                "column_id": "string",
+                "column_type": "string",
+                "formula": "string (optional)",
+            },
+        },
+        "modify_column": {
+            "description": "Modify a column's type or formula",
+            "fields": {
+                "table": "string",
+                "column_id": "string",
+                "type": "string (optional)",
+                "formula": "string (optional)",
+            },
+        },
+        "delete_column": {
+            "description": "Delete a column",
+            "fields": {"table": "string", "column_id": "string"},
+        },
+    },
+    "response_format": {
+        "success": {"success": True, "data": "..."},
+        "error": {"success": False, "error": "message", "code": "ERROR_CODE"},
+    },
+    "error_codes": [
+        "UNAUTHORIZED",
+        "INVALID_TOKEN",
+        "TOKEN_EXPIRED",
+        "INVALID_REQUEST",
+        "GRIST_ERROR",
+    ],
+    "example_script": """#!/usr/bin/env python3
+import requests
+import sys
+
+# Use token and proxy_url from request_session_token response
+token = sys.argv[1]
+proxy_url = sys.argv[2]
+
+response = requests.post(
+    proxy_url,
+    headers={'Authorization': f'Bearer {token}'},
+    json={
+        'method': 'add_records',
+        'table': 'Orders',
+        'records': [{'item': 'Widget', 'qty': 100}]
+    }
+)
+print(response.json())
+""",
+}
+
+
+async def get_proxy_documentation() -> dict:
+    """Return complete documentation for the HTTP proxy API."""
+    return PROXY_DOCUMENTATION
+
+
+async def request_session_token(
+    agent: Agent,
+    auth: Authenticator,
+    token_manager: SessionTokenManager,
+    document: str,
+    permissions: list[str],
+    ttl_seconds: int = 300,
+    proxy_base_url: str | None = None,
+) -> dict:
+    """Request a short-lived session token for HTTP proxy access.
+
+    The token can only grant permissions the agent already has.
+    """
+    # Verify agent has access to the document
+    # Check each requested permission
+    for perm_str in permissions:
+        try:
+            perm = Permission(perm_str)
+        except ValueError:
+            raise AuthError(f"Invalid permission: {perm_str}")
+        auth.authorize(agent, document, perm)
+
+    # Create the session token
+    session = token_manager.create_token(
+        agent_name=agent.name,
+        document=document,
+        permissions=permissions,
+        ttl_seconds=ttl_seconds,
+    )
+
+    # Build proxy URL - use base URL if provided, otherwise just path
+    proxy_path = "/api/v1/proxy"
+    if proxy_base_url:
+        proxy_url = f"{proxy_base_url.rstrip('/')}{proxy_path}"
+    else:
+        proxy_url = proxy_path
+
+    return {
+        "token": session.token,
+        "document": session.document,
+        "permissions": session.permissions,
+        "expires_at": session.expires_at.isoformat(),
+        "proxy_url": proxy_url,
+    }

src/grist_mcp/tools/write.py

@@ -1,4 +1,7 @@
-"""Write tools - create, update, delete records."""
+"""Write tools - create, update, delete records, upload attachments."""
+
+import base64
+import mimetypes
 
 from grist_mcp.auth import Agent, Authenticator, Permission
 from grist_mcp.grist_client import GristClient
@@ -59,3 +62,50 @@ async def delete_records(
 
     await client.delete_records(table, record_ids)
     return {"deleted": True}
+
+
+async def upload_attachment(
+    agent: Agent,
+    auth: Authenticator,
+    document: str,
+    filename: str,
+    content_base64: str,
+    content_type: str | None = None,
+    client: GristClient | None = None,
+) -> dict:
+    """Upload a file attachment to a document.
+
+    Args:
+        agent: The authenticated agent.
+        auth: Authenticator for permission checks.
+        document: Document name.
+        filename: Filename with extension.
+        content_base64: File content as base64-encoded string.
+        content_type: MIME type (auto-detected from filename if omitted).
+        client: Optional GristClient instance.
+
+    Returns:
+        Dict with attachment_id, filename, and size_bytes.
+
+    Raises:
+        ValueError: If content_base64 is not valid base64.
+    """
+    auth.authorize(agent, document, Permission.WRITE)
+
+    # Decode base64 content
+    try:
+        content = base64.b64decode(content_base64)
+    except Exception:
+        raise ValueError("Invalid base64 encoding")
+
+    # Auto-detect MIME type if not provided
+    if content_type is None:
+        content_type, _ = mimetypes.guess_type(filename)
+        if content_type is None:
+            content_type = "application/octet-stream"
+
+    if client is None:
+        doc = auth.get_document(document)
+        client = GristClient(doc)
+
+    return await client.upload_attachment(filename, content, content_type)

tests/integration/mock_grist/server.py

@@ -178,6 +178,15 @@ async def modify_column(request):
     return JSONResponse({})
 
 
+async def modify_columns(request):
+    """PATCH /api/docs/{doc_id}/tables/{table_id}/columns - batch modify columns"""
+    doc_id = request.path_params["doc_id"]
+    table_id = request.path_params["table_id"]
+    body = await request.json()
+    log_request("PATCH", f"/api/docs/{doc_id}/tables/{table_id}/columns", body)
+    return JSONResponse({})
+
+
 async def delete_column(request):
     """DELETE /api/docs/{doc_id}/tables/{table_id}/columns/{col_id}"""
     doc_id = request.path_params["doc_id"]
@@ -199,6 +208,7 @@ app = Starlette(
         Route("/api/docs/{doc_id}/tables", endpoint=create_tables, methods=["POST"]),
         Route("/api/docs/{doc_id}/tables/{table_id}/columns", endpoint=get_table_columns),
         Route("/api/docs/{doc_id}/tables/{table_id}/columns", endpoint=add_column, methods=["POST"]),
+        Route("/api/docs/{doc_id}/tables/{table_id}/columns", endpoint=modify_columns, methods=["PATCH"]),
         Route("/api/docs/{doc_id}/tables/{table_id}/columns/{col_id}", endpoint=modify_column, methods=["PATCH"]),
         Route("/api/docs/{doc_id}/tables/{table_id}/columns/{col_id}", endpoint=delete_column, methods=["DELETE"]),
         Route("/api/docs/{doc_id}/tables/{table_id}/records", endpoint=get_records),

tests/integration/test_mcp_protocol.py

@@ -9,12 +9,14 @@ from mcp.client.sse import sse_client
 
 
 GRIST_MCP_URL = os.environ.get("GRIST_MCP_URL", "http://localhost:3000")
+GRIST_MCP_TOKEN = os.environ.get("GRIST_MCP_TOKEN", "test-token")
 
 
 @asynccontextmanager
 async def create_mcp_session():
     """Create and yield an MCP session."""
-    async with sse_client(f"{GRIST_MCP_URL}/sse") as (read_stream, write_stream):
+    headers = {"Authorization": f"Bearer {GRIST_MCP_TOKEN}"}
+    async with sse_client(f"{GRIST_MCP_URL}/sse", headers=headers) as (read_stream, write_stream):
         async with ClientSession(read_stream, write_stream) as session:
             await session.initialize()
             yield session
@@ -44,12 +46,14 @@ async def test_mcp_protocol_compliance(services_ready):
             "add_column",
             "modify_column",
             "delete_column",
+            "get_proxy_documentation",
+            "request_session_token",
         ]
 
         for expected in expected_tools:
             assert expected in tool_names, f"Missing tool: {expected}"
 
-        assert len(result.tools) == 12, f"Expected 12 tools, got {len(result.tools)}"
+        assert len(result.tools) == 14, f"Expected 14 tools, got {len(result.tools)}"
 
         # Test 3: All tools have descriptions
         for tool in result.tools:

tests/integration/test_session_proxy.py

@@ -0,0 +1,52 @@
+"""Integration tests for session token proxy."""
+
+import os
+import pytest
+import httpx
+
+
+GRIST_MCP_URL = os.environ.get("GRIST_MCP_URL", "http://localhost:3000")
+GRIST_MCP_TOKEN = os.environ.get("GRIST_MCP_TOKEN")
+
+
+@pytest.fixture
+def mcp_client():
+    """Client for MCP SSE endpoint."""
+    return httpx.Client(
+        base_url=GRIST_MCP_URL,
+        headers={"Authorization": f"Bearer {GRIST_MCP_TOKEN}"},
+    )
+
+
+@pytest.fixture
+def proxy_client():
+    """Client for proxy endpoint (session token set per-test)."""
+    return httpx.Client(base_url=GRIST_MCP_URL)
+
+
+@pytest.mark.integration
+def test_full_session_proxy_flow(mcp_client, proxy_client):
+    """Test: request token via MCP, use token to call proxy."""
+    # This test requires a running grist-mcp server with proper config
+    # Skip if not configured
+    if not GRIST_MCP_TOKEN:
+        pytest.skip("GRIST_MCP_TOKEN not set")
+
+    # Step 1: Request session token (would be via MCP in real usage)
+    # For integration test, we test the proxy endpoint directly
+    # This is a placeholder - full MCP integration would use SSE
+
+    # Step 2: Use proxy endpoint
+    # Note: Need a valid session token to test this fully
+    # For now, verify endpoint exists and rejects bad tokens
+
+    response = proxy_client.post(
+        "/api/v1/proxy",
+        headers={"Authorization": "Bearer invalid_token"},
+        json={"method": "list_tables"},
+    )
+
+    assert response.status_code == 401
+    data = response.json()
+    assert data["success"] is False
+    assert data["code"] in ["INVALID_TOKEN", "TOKEN_EXPIRED"]

tests/integration/test_tools_integration.py

@@ -12,12 +12,14 @@ from mcp.client.sse import sse_client
 
 GRIST_MCP_URL = os.environ.get("GRIST_MCP_URL", "http://localhost:3000")
 MOCK_GRIST_URL = os.environ.get("MOCK_GRIST_URL", "http://localhost:8484")
+GRIST_MCP_TOKEN = os.environ.get("GRIST_MCP_TOKEN", "test-token")
 
 
 @asynccontextmanager
 async def create_mcp_session():
     """Create and yield an MCP session."""
-    async with sse_client(f"{GRIST_MCP_URL}/sse") as (read_stream, write_stream):
+    headers = {"Authorization": f"Bearer {GRIST_MCP_TOKEN}"}
+    async with sse_client(f"{GRIST_MCP_URL}/sse", headers=headers) as (read_stream, write_stream):
         async with ClientSession(read_stream, write_stream) as session:
             await session.initialize()
             yield session
@@ -194,7 +196,7 @@ async def test_all_tools(services_ready):
         data = json.loads(result.content[0].text)
         assert "modified" in data
         log = get_mock_request_log()
-        patch_cols = [e for e in log if e["method"] == "PATCH" and "/columns/" in e["path"]]
+        patch_cols = [e for e in log if e["method"] == "PATCH" and "/columns" in e["path"]]
         assert len(patch_cols) >= 1
 
         # Test delete_column

tests/unit/test_grist_client.py

@@ -196,3 +196,43 @@ def test_sql_validation_rejects_multiple_statements(client):
 def test_sql_validation_allows_trailing_semicolon(client):
     # Should not raise
     client._validate_sql_query("SELECT * FROM users;")
+
+
+# Attachment tests
+
+@pytest.mark.asyncio
+async def test_upload_attachment(client, httpx_mock: HTTPXMock):
+    httpx_mock.add_response(
+        url="https://grist.example.com/api/docs/abc123/attachments",
+        method="POST",
+        json=[42],
+    )
+
+    result = await client.upload_attachment(
+        filename="invoice.pdf",
+        content=b"PDF content here",
+        content_type="application/pdf",
+    )
+
+    assert result == {
+        "attachment_id": 42,
+        "filename": "invoice.pdf",
+        "size_bytes": 16,
+    }
+
+
+@pytest.mark.asyncio
+async def test_upload_attachment_default_content_type(client, httpx_mock: HTTPXMock):
+    httpx_mock.add_response(
+        url="https://grist.example.com/api/docs/abc123/attachments",
+        method="POST",
+        json=[99],
+    )
+
+    result = await client.upload_attachment(
+        filename="data.bin",
+        content=b"\x00\x01\x02",
+    )
+
+    assert result["attachment_id"] == 99
+    assert result["size_bytes"] == 3

tests/unit/test_proxy.py

@@ -0,0 +1,98 @@
+from datetime import datetime, timezone
+from unittest.mock import AsyncMock, MagicMock
+
+import pytest
+
+from grist_mcp.proxy import parse_proxy_request, ProxyRequest, ProxyError, dispatch_proxy_request
+from grist_mcp.session import SessionToken
+
+
+@pytest.fixture
+def mock_session():
+    return SessionToken(
+        token="sess_test",
+        document="sales",
+        permissions=["read", "write"],
+        agent_name="test-agent",
+        created_at=datetime.now(timezone.utc),
+        expires_at=datetime.now(timezone.utc),
+    )
+
+
+@pytest.fixture
+def mock_auth():
+    auth = MagicMock()
+    doc = MagicMock()
+    doc.url = "https://grist.example.com"
+    doc.doc_id = "abc123"
+    doc.api_key = "key"
+    auth.get_document.return_value = doc
+    return auth
+
+
+def test_parse_proxy_request_valid_add_records():
+    body = {
+        "method": "add_records",
+        "table": "Orders",
+        "records": [{"item": "Widget", "qty": 10}],
+    }
+
+    request = parse_proxy_request(body)
+
+    assert request.method == "add_records"
+    assert request.table == "Orders"
+    assert request.records == [{"item": "Widget", "qty": 10}]
+
+
+def test_parse_proxy_request_missing_method():
+    body = {"table": "Orders"}
+
+    with pytest.raises(ProxyError) as exc_info:
+        parse_proxy_request(body)
+
+    assert exc_info.value.code == "INVALID_REQUEST"
+    assert "method" in str(exc_info.value)
+
+
+@pytest.mark.asyncio
+async def test_dispatch_add_records(mock_session, mock_auth):
+    request = ProxyRequest(
+        method="add_records",
+        table="Orders",
+        records=[{"item": "Widget"}],
+    )
+
+    mock_client = AsyncMock()
+    mock_client.add_records.return_value = [1, 2, 3]
+
+    result = await dispatch_proxy_request(
+        request, mock_session, mock_auth, client=mock_client
+    )
+
+    assert result["success"] is True
+    assert result["data"]["record_ids"] == [1, 2, 3]
+    mock_client.add_records.assert_called_once_with("Orders", [{"item": "Widget"}])
+
+
+@pytest.mark.asyncio
+async def test_dispatch_denies_without_permission(mock_auth):
+    # Session only has read permission
+    session = SessionToken(
+        token="sess_test",
+        document="sales",
+        permissions=["read"],  # No write
+        agent_name="test-agent",
+        created_at=datetime.now(timezone.utc),
+        expires_at=datetime.now(timezone.utc),
+    )
+
+    request = ProxyRequest(
+        method="add_records",  # Requires write
+        table="Orders",
+        records=[{"item": "Widget"}],
+    )
+
+    with pytest.raises(ProxyError) as exc_info:
+        await dispatch_proxy_request(request, session, mock_auth)
+
+    assert exc_info.value.code == "UNAUTHORIZED"

tests/unit/test_server.py

@@ -52,6 +52,50 @@ tokens:
     assert "add_column" in tool_names
     assert "modify_column" in tool_names
     assert "delete_column" in tool_names
+    assert "upload_attachment" in tool_names
 
-    # Should have all 12 tools
+    # Session tools (always registered)
-    assert len(result.root.tools) == 12
+    assert "get_proxy_documentation" in tool_names
+    assert "request_session_token" in tool_names
+
+    # Should have all 15 tools
+    assert len(result.root.tools) == 15
+
+
+@pytest.mark.asyncio
+async def test_create_server_registers_session_tools(tmp_path):
+    from grist_mcp.session import SessionTokenManager
+
+    config_file = tmp_path / "config.yaml"
+    config_file.write_text("""
+documents:
+  test-doc:
+    url: https://grist.example.com
+    doc_id: abc123
+    api_key: test-key
+
+tokens:
+  - token: valid-token
+    name: test-agent
+    scope:
+      - document: test-doc
+        permissions: [read, write, schema]
+""")
+
+    config = load_config(str(config_file))
+    auth = Authenticator(config)
+    agent = auth.authenticate("valid-token")
+    token_manager = SessionTokenManager()
+    server = create_server(auth, agent, token_manager)
+
+    # Get the list_tools handler and call it
+    handler = server.request_handlers.get(ListToolsRequest)
+    assert handler is not None
+
+    req = ListToolsRequest(method="tools/list")
+    result = await handler(req)
+
+    tool_names = [t.name for t in result.root.tools]
+
+    assert "get_proxy_documentation" in tool_names
+    assert "request_session_token" in tool_names

tests/unit/test_session.py

@@ -0,0 +1,81 @@
+import pytest
+from datetime import datetime, timedelta, timezone
+
+from grist_mcp.session import SessionTokenManager, SessionToken
+
+
+def test_create_token_returns_valid_session_token():
+    manager = SessionTokenManager()
+
+    token = manager.create_token(
+        agent_name="test-agent",
+        document="sales",
+        permissions=["read", "write"],
+        ttl_seconds=300,
+    )
+
+    assert token.token.startswith("sess_")
+    assert len(token.token) > 20
+    assert token.document == "sales"
+    assert token.permissions == ["read", "write"]
+    assert token.agent_name == "test-agent"
+    assert token.expires_at > datetime.now(timezone.utc)
+    assert token.expires_at < datetime.now(timezone.utc) + timedelta(seconds=310)
+
+
+def test_create_token_caps_ttl_at_maximum():
+    manager = SessionTokenManager()
+
+    # Request 2 hours, should be capped at 1 hour
+    token = manager.create_token(
+        agent_name="test-agent",
+        document="sales",
+        permissions=["read"],
+        ttl_seconds=7200,
+    )
+
+    # Should be capped at 3600 seconds (1 hour)
+    max_expires = datetime.now(timezone.utc) + timedelta(seconds=3610)
+    assert token.expires_at < max_expires
+
+
+def test_validate_token_returns_session_for_valid_token():
+    manager = SessionTokenManager()
+    created = manager.create_token(
+        agent_name="test-agent",
+        document="sales",
+        permissions=["read"],
+        ttl_seconds=300,
+    )
+
+    session = manager.validate_token(created.token)
+
+    assert session is not None
+    assert session.document == "sales"
+    assert session.agent_name == "test-agent"
+
+
+def test_validate_token_returns_none_for_unknown_token():
+    manager = SessionTokenManager()
+
+    session = manager.validate_token("sess_unknown_token")
+
+    assert session is None
+
+
+def test_validate_token_returns_none_for_expired_token():
+    manager = SessionTokenManager()
+    created = manager.create_token(
+        agent_name="test-agent",
+        document="sales",
+        permissions=["read"],
+        ttl_seconds=1,
+    )
+
+    # Wait for expiry
+    import time
+    time.sleep(1.5)
+
+    session = manager.validate_token(created.token)
+
+    assert session is None

tests/unit/test_tools_session.py

@@ -0,0 +1,122 @@
+import pytest
+from grist_mcp.tools.session import get_proxy_documentation, request_session_token
+from grist_mcp.auth import Authenticator, Agent, AuthError
+from grist_mcp.config import Config, Document, Token, TokenScope
+from grist_mcp.session import SessionTokenManager
+
+
+@pytest.fixture
+def sample_config():
+    return Config(
+        documents={
+            "sales": Document(
+                url="https://grist.example.com",
+                doc_id="abc123",
+                api_key="key",
+            ),
+        },
+        tokens=[
+            Token(
+                token="agent-token",
+                name="test-agent",
+                scope=[
+                    TokenScope(document="sales", permissions=["read", "write"]),
+                ],
+            ),
+        ],
+    )
+
+
+@pytest.fixture
+def auth_and_agent(sample_config):
+    auth = Authenticator(sample_config)
+    agent = auth.authenticate("agent-token")
+    return auth, agent
+
+
+@pytest.mark.asyncio
+async def test_get_proxy_documentation_returns_complete_spec():
+    result = await get_proxy_documentation()
+
+    assert "description" in result
+    assert "endpoint" in result
+    assert result["endpoint"] == "POST /api/v1/proxy"
+    assert "authentication" in result
+    assert "methods" in result
+    assert "add_records" in result["methods"]
+    assert "get_records" in result["methods"]
+    assert "example_script" in result
+
+
+@pytest.mark.asyncio
+async def test_request_session_token_creates_valid_token(auth_and_agent):
+    auth, agent = auth_and_agent
+    manager = SessionTokenManager()
+
+    result = await request_session_token(
+        agent=agent,
+        auth=auth,
+        token_manager=manager,
+        document="sales",
+        permissions=["read", "write"],
+        ttl_seconds=300,
+    )
+
+    assert "token" in result
+    assert result["token"].startswith("sess_")
+    assert result["document"] == "sales"
+    assert result["permissions"] == ["read", "write"]
+    assert "expires_at" in result
+    assert result["proxy_url"] == "/api/v1/proxy"
+
+
+@pytest.mark.asyncio
+async def test_request_session_token_rejects_unauthorized_document(sample_config):
+    auth = Authenticator(sample_config)
+    agent = auth.authenticate("agent-token")
+    manager = SessionTokenManager()
+
+    with pytest.raises(AuthError, match="Document not in scope"):
+        await request_session_token(
+            agent=agent,
+            auth=auth,
+            token_manager=manager,
+            document="unauthorized_doc",
+            permissions=["read"],
+            ttl_seconds=300,
+        )
+
+
+@pytest.mark.asyncio
+async def test_request_session_token_rejects_unauthorized_permission(sample_config):
+    auth = Authenticator(sample_config)
+    agent = auth.authenticate("agent-token")
+    manager = SessionTokenManager()
+
+    # Agent has read/write on sales, but not schema
+    with pytest.raises(AuthError, match="Permission denied"):
+        await request_session_token(
+            agent=agent,
+            auth=auth,
+            token_manager=manager,
+            document="sales",
+            permissions=["read", "schema"],  # schema not granted
+            ttl_seconds=300,
+        )
+
+
+@pytest.mark.asyncio
+async def test_request_session_token_rejects_invalid_permission(sample_config):
+    auth = Authenticator(sample_config)
+    agent = auth.authenticate("agent-token")
+    manager = SessionTokenManager()
+
+    with pytest.raises(AuthError, match="Invalid permission"):
+        await request_session_token(
+            agent=agent,
+            auth=auth,
+            token_manager=manager,
+            document="sales",
+            permissions=["read", "invalid_perm"],
+            ttl_seconds=300,
+        )

tests/unit/test_tools_write.py

@@ -1,7 +1,9 @@
+import base64
+
 import pytest
 from unittest.mock import AsyncMock
 
-from grist_mcp.tools.write import add_records, update_records, delete_records
+from grist_mcp.tools.write import add_records, update_records, delete_records, upload_attachment
 from grist_mcp.auth import Authenticator, AuthError
 from grist_mcp.config import Config, Document, Token, TokenScope
 
@@ -94,3 +96,105 @@ async def test_delete_records(auth, mock_client):
     )
 
     assert result == {"deleted": True}
+
+
+# Upload attachment tests
+
+@pytest.fixture
+def mock_client_with_attachment():
+    client = AsyncMock()
+    client.upload_attachment.return_value = {
+        "attachment_id": 42,
+        "filename": "invoice.pdf",
+        "size_bytes": 1024,
+    }
+    return client
+
+
+@pytest.mark.asyncio
+async def test_upload_attachment_success(auth, mock_client_with_attachment):
+    agent = auth.authenticate("write-token")
+    content = b"PDF content"
+    content_base64 = base64.b64encode(content).decode()
+
+    result = await upload_attachment(
+        agent, auth, "budget",
+        filename="invoice.pdf",
+        content_base64=content_base64,
+        client=mock_client_with_attachment,
+    )
+
+    assert result == {
+        "attachment_id": 42,
+        "filename": "invoice.pdf",
+        "size_bytes": 1024,
+    }
+    mock_client_with_attachment.upload_attachment.assert_called_once_with(
+        "invoice.pdf", content, "application/pdf"
+    )
+
+
+@pytest.mark.asyncio
+async def test_upload_attachment_invalid_base64(auth, mock_client_with_attachment):
+    agent = auth.authenticate("write-token")
+
+    with pytest.raises(ValueError, match="Invalid base64 encoding"):
+        await upload_attachment(
+            agent, auth, "budget",
+            filename="test.txt",
+            content_base64="not-valid-base64!!!",
+            client=mock_client_with_attachment,
+        )
+
+
+@pytest.mark.asyncio
+async def test_upload_attachment_auth_required(auth, mock_client_with_attachment):
+    agent = auth.authenticate("read-token")
+    content_base64 = base64.b64encode(b"test").decode()
+
+    with pytest.raises(AuthError, match="Permission denied"):
+        await upload_attachment(
+            agent, auth, "budget",
+            filename="test.txt",
+            content_base64=content_base64,
+            client=mock_client_with_attachment,
+        )
+
+
+@pytest.mark.asyncio
+async def test_upload_attachment_mime_detection(auth, mock_client_with_attachment):
+    agent = auth.authenticate("write-token")
+    content = b"PNG content"
+    content_base64 = base64.b64encode(content).decode()
+
+    await upload_attachment(
+        agent, auth, "budget",
+        filename="image.png",
+        content_base64=content_base64,
+        client=mock_client_with_attachment,
+    )
+
+    # Should auto-detect image/png from filename
+    mock_client_with_attachment.upload_attachment.assert_called_once_with(
+        "image.png", content, "image/png"
+    )
+
+
+@pytest.mark.asyncio
+async def test_upload_attachment_explicit_content_type(auth, mock_client_with_attachment):
+    agent = auth.authenticate("write-token")
+    content = b"custom content"
+    content_base64 = base64.b64encode(content).decode()
+
+    await upload_attachment(
+        agent, auth, "budget",
+        filename="file.dat",
+        content_base64=content_base64,
+        content_type="application/custom",
+        client=mock_client_with_attachment,
+    )
+
+    # Should use explicit content type
+    mock_client_with_attachment.upload_attachment.assert_called_once_with(
+        "file.dat", content, "application/custom"
+    )

uv.lock

@@ -153,7 +153,7 @@ wheels = [
 
 [[package]]
 name = "grist-mcp"
-version = "1.1.0"
+version = "1.2.0"
 source = { editable = "." }
 dependencies = [
     { name = "httpx" },