RFC: Automated toolchain version monitoring and upgrade workflow

## Problem

Several runtime dependencies in the agent Dockerfile and `pyproject.toml` are manually pinned with no automated notification when new versions are available:

| Dependency | Current Pin | Update Frequency | Risk of Stale |
|---|---|---|---|
| Node.js | `setup_24.x` (LTS) | ~6 months (LTS cycle) | Medium |
| Claude Code CLI | `@anthropic-ai/claude-code@2.1.142` | Weekly+ | High |
| claude-agent-sdk | `claude-agent-sdk==0.2.82` | Weekly+ (bundles CLI) | **High** |
| boto3 | `boto3==1.43.6` | Weekly (AWS SDK releases) | **High** |
| Go (gh builder) | `golang:1.26.3-bookworm` | ~6 months | Low |
| gh CLI | `GH_VERSION=2.92.0` | Monthly | Low |
| Python base | `python:3.13-slim` | ~12 months | Low |
| uv | `ghcr.io/astral-sh/uv:0.11.14` | Multiple times/week | Medium |

### Key coupling: claude-agent-sdk ↔ Claude Code CLI

The `claude-agent-sdk` Python package **bundles** the Claude Code CLI binary inside its wheel. The Dockerfile also installs the CLI separately via npm. These versions **must stay in sync**:
- `pyproject.toml`: `claude-agent-sdk==0.2.82` → bundles CLI 2.1.142
- `Dockerfile`: `@anthropic-ai/claude-code@2.1.142`

When upgrading either, check the [SDK release notes](https://github.com/anthropics/claude-agent-sdk-python/releases) to find which CLI version it bundles, then update both.

### boto3 releases frequently

AWS releases `boto3` multiple times per week. Each release adds new service APIs and bug fixes. Falling behind risks missing security patches and new features needed for AgentCore/Bedrock.

## Proposal

### Option A: Dependabot (recommended)

Dependabot is GitHub-native (no license concerns) and covers the ecosystems that matter most:

| Ecosystem | Directory | What it monitors | Value |
|---|---|---|---|
| `github-actions` | `/.github/workflows/` | SHA-pinned action versions (7 actions) | **Highest** — nothing else does this |
| `docker` | `/agent/` | `FROM` image tags (golang, python) | **High** — Trivy flags CVEs but doesn't propose base-image bumps |
| `npm` | `/` | Yarn workspace dependencies | **Moderate** — osv-scanner/Retire cover CVEs but not freshness |
| `pip` | `/agent/` | pyproject.toml + uv.lock ([supported](https://docs.github.com/en/code-security/reference/supply-chain-security/supported-ecosystems-and-repositories)) | **High** — covers boto3, claude-agent-sdk, fastapi, etc. |

### Option B: Scheduled GitHub Action (for Dockerfile pin gaps)

Dependabot cannot parse version strings inside `RUN` commands or `ARG` values. A weekly Action would cover:
1. **Claude Code CLI**: compare `@anthropic-ai/claude-code@X` vs `npm view @anthropic-ai/claude-code version`
2. **claude-agent-sdk**: compare pinned vs latest [SDK release](https://github.com/anthropics/claude-agent-sdk-python/releases) and extract bundled CLI version
3. **gh CLI**: compare `GH_VERSION` ARG vs latest `cli/cli` release
4. **uv**: compare pinned COPY tag vs latest `astral-sh/uv` release
5. Opens an issue when versions drift, noting the coupling between SDK and CLI

### What each tool covers

| Dependency | Dependabot? | Custom Action? | Notes |
|---|---|---|---|
| claude-agent-sdk | Yes (pip) | Yes (coupling check) | Dependabot bumps the pin; Action verifies CLI alignment |
| Claude Code CLI (Dockerfile) | No | Yes | Inside `RUN` command, not parseable |
| boto3 | Yes (pip) | No | Standard Dependabot pip coverage |
| Node.js (Dockerfile) | No | Possible | Inside `curl` command, not parseable |
| Go builder image | Yes (docker) | No | `FROM golang:X` tag |
| Python base image | Yes (docker) | No | `FROM python:X` tag |
| gh CLI (ARG) | No | Yes | `ARG GH_VERSION=X` not parseable |
| uv (COPY --from) | Yes (docker) | No | `COPY --from=ghcr.io/astral-sh/uv:X` is a docker ref |
| GitHub Actions | Yes (github-actions) | No | SHA pins auto-bumped |
| npm deps (CDK, CLI, docs) | Yes (npm) | No | Yarn workspace coverage |

## Implementation Plan

- [ ] Add `.github/dependabot.yml` with `github-actions`, `docker`, `npm`, and `pip` ecosystems
- [ ] Configure grouping (e.g., group minor/patch boto3 updates, group AWS SDK updates)
- [ ] Set `open-pull-requests-limit` per ecosystem to manage PR noise
- [ ] Create scheduled Action for Dockerfile pin monitoring (Claude Code CLI ↔ SDK coupling, gh, Node)
- [ ] Document the SDK ↔ CLI coupling in AGENTS.md or CONTRIBUTING.md

## Related Issues

- #105 — Upgrade Python 3.13 → 3.14
- #106 — Upgrade Debian bookworm → trixie
- PR #103 — Node.js 20→24, Claude Code 2.1.142, pin uv 0.11.14, claude-agent-sdk 0.2.82

## References

- [Node.js release schedule](https://nodejs.org/en/about/previous-releases)
- [claude-agent-sdk releases](https://github.com/anthropics/claude-agent-sdk-python/releases)
- [Dependabot Docker support](https://docs.github.com/en/code-security/dependabot/dependabot-version-updates/configuration-options-for-the-dependabot.yml-file#docker-ecosystem)
- [Dependabot GitHub Actions support](https://docs.github.com/en/code-security/dependabot/dependabot-version-updates/configuration-options-for-the-dependabot.yml-file#github-actions)
- [Dependabot pip/uv.lock support](https://docs.github.com/en/code-security/reference/supply-chain-security/supported-ecosystems-and-repositories)

Beginne mit der Untersuchung des agent Dockerfile, der pyproject.toml, der vorhandenen Workflows unter /.github/workflows/ und der Abhängigkeitsstruktur unter /agent/. Überprüfe die Abdeckung der Dependabot-Ökosysteme und die geplante zeitgesteuerte Action, insbesondere die Kopplung von claude-agent-sdk und der Claude Code CLI. Als abgeschlossen gilt die Aufgabe, wenn die Dependabot-Konfiguration, der Monitoring-Workflow und die Dokumentation zur Kopplung wie in der Checkliste beschrieben implementiert sind.

Vom Indexierungsmodell aus dem Issue-Text verfasst.