# Bwrap runtime and private state `ext.bwrap` can mount a standalone Python runtime selected by the owner's extension configuration. A create/exec caller cannot select host paths or replace the sanitized child environment. ```yaml config: runtime: path: /srv/sandboxer/runtimes/rein-aharness-example sha256: ``` The path must be a canonical absolute directory with `pyvenv.cfg` and `bin/python3`. Its complete tree digest includes file contents, modes, directory entries, and internal symlinks. Absolute/escaping symlinks and special files are refused. Missing files, added files, changed permissions, or changed content invalidate the pin. The runtime must not overlap the source checkout or writable sandbox workspace. The owner mounts the artifact read-only at `/opt/sandboxer/runtime` and prepends its `bin` directory to the child PATH. Console entrypoints must use that fixed mount prefix. Artifacts remain an owner trust boundary: publish them in a protected location and do not mutate them while sandboxes use them. Digest validation occurs at creation; it is not a mechanism for making a mutable host directory immutable to its owner. ## Building and testing the Python rein bundle From this repository, with committed rein/llm-connect source checkouts: ```bash uv run python scripts/build-rein-runtime.py \ --output /tmp/rein-runtime-candidate \ --rein-source ../rein-aharness \ --llm-source ../llm-connect ``` The builder creates a standalone system-Python venv, installs both packages non-editably with their dependencies, rewrites Python console entrypoint shebangs to the fixed mount path, and records source revisions plus resolved package versions in `build-info.json`. It prints the resulting path/digest. Dependency versions are resolved during this candidate build; the digest pins the produced artifact, not a promise that another build will be bit-identical. No interactive home, credentials, or provider login is copied into the bundle. Prove the artifact using the returned values: ```bash uv run python scripts/smoke-bwrap-runtime.py \ --runtime-path /tmp/rein-runtime-candidate \ --runtime-sha256 ``` The smoke uses an isolated owner extension configuration and the real broker. It imports the rein's Claude adapter and llm-connect, runs `rein-aharness --help`, proves the runtime rejects writes, writes private state outside the worktree, verifies source absence and a clean Git tree, checks loopback-only networking, and tears down. This is real CLI startup, not a model task. The default Python-only build does not package Claude. The optional explicit Claude pin and isolated startup proof are documented in the later candidate section below; production authentication remains a separate gate. No committed profile selects a temporary `/tmp` build as its production runtime. ## Private writable state The broker creates mode-0700 directories in the namespace's temporary root: | Environment variable | Location | |---|---| | `HOME` | `/run/sandboxer/state/home` | | `XDG_CONFIG_HOME` | `/run/sandboxer/state/config` | | `XDG_CACHE_HOME` | `/run/sandboxer/state/cache` | | `XDG_STATE_HOME` | `/run/sandboxer/state/data` | | `TMPDIR` | `/run/sandboxer/state/tmp` | These directories persist between exec requests in the same sandbox, remain outside the Git worktree, and disappear with namespace teardown. Python user site packages and bytecode writes are disabled. The owner's child environment continues to carry exact consumer identity and value-free route references. ## Network and credentials remain separate gates Bwrap refuses `network.default: allow` and setup secret references. Network egress is opt-in through the owner allowlist described in bwrap-egress.md; empty-egress profiles retain loopback-only networking. Credential exec delivery is now opt-in through the owner route contract in bwrap-credentials.md; no production route is active. Returning a declared egress list as evidence would not make that list enforced or usable. Exec credential route references contain no values. Nonempty references now require an owner-configured, consumer-bound provider; references alone grant nothing. On 2026-09-05, `warden route find anthropic --json` and `warden route find claude-code --json` returned no matching workload routes. The generic OpenBao entry is explicitly a routing template, not an executable credential lane. The OpenRouter AppRole route belongs to the other rein and is not a substitute for Claude authentication. `SAND-WP-0015-T04` / `SAND-WP-0014-T05` and `GLAS-WP-0012-T02` retain the production requirements: a concrete owner-approved Claude credential route, delivery and revocation semantics, a pinned Claude runtime, and explicitly enforced provider egress with negative tests. Glas local profiles remain blocked until those requirements and the real-model acceptance pass. ## 2026-09-05 candidate evidence Runtime SHA-256: `4c316737ec2715936a12c4f49621a5e4be3d1f4fe4739130393f28cdda66fbd9`. Candidate path: `/tmp/sandboxer-rein-aharness-runtime-20260905-v2`. Source revisions: rein-aharness `1429db5ad4c83331b6375349ffde1eb13af9575b`, llm-connect `00560945f81ba6ff1f5cacd9fe99c7fe756cc4b1`; Python 3.12.3. Sandbox `f333fb66` passed the real CLI/import/read-only/private-state smoke. `sys.prefix` was `/opt/sandboxer/runtime`, HOME was outside the worktree with mode 0700, Git stayed clean, source was absent, only `lo` existed, credential references were empty, and the workspace was removed. No model request or credential acquisition occurred. Final validation: `make check` passed lint and 132 tests. Authenticated owner API smoke `223db65b` returned HTTP 200 with exact identity/stdin and complete teardown. Follow-up runtime smoke `d4de9531` repeated the real CLI/startup checks and proved private state survives a second exec in the same namespace. The default unconfigured `profile.bwrap-local` still has no selected rein bundle; candidate startup does not constitute production deployment. ## 2026-09-06 combined-runtime return to Glas (GLAS-WP-0015 handoff) Returned for `GLAS-WP-0012` review of revision 1.1.0. Nothing here is activated. | Field | Value | |---|---| | Profile | `profile.claude-agent-dev-proof`, version `1.1.0`, `ext.bwrap` | | Host scope | `localhost` only (`placement.prefer: [localhost]`, no fallback) | | Consumer tuple | `actor: agt`, `project: glas-local-proof`, nonempty `run_id` | | Credential route | `glas-claude-agent-dev-anthropic`, exec-env, `ANTHROPIC_API_KEY` | | Declared egress | `api.anthropic.com:443`, under `network.default: deny` | | Python runtime digest | `4c316737ec2715936a12c4f49621a5e4be3d1f4fe4739130393f28cdda66fbd9` | | Runtime mount | read-only `/opt/sandboxer/runtime`, `bin` prepended to child PATH | | Runtime sources | rein-aharness `1429db5`, llm-connect `0056094`, Python 3.12.3 | | Claude executable | **not pinned** — no path, no digest, no startup proof | The project example is reconciled to the acceptance runner's `glas-local-proof`; the route is not broadened to other Glas projects. See bwrap-credentials.md. Denial and cleanup evidence already recorded, all value-free: wrong-project credential denial and next-exec key absence in sandbox `0e5fb35a`; undeclared `example.com` and direct `1.1.1.1:443` denial with proxy/workspace teardown in sandbox `e290e788`; read-only runtime, private 0700 HOME, clean worktree, absent source and loopback-only networking in sandboxes `f333fb66` / `d4de9531`. The committed profile declares egress but grants none: `ext.bwrap` refuses it unless the owner extension config independently allowlists the destination, and a regression test asserts that fail-closed default. Still operator-blocked, so this profile stays unready: the concrete Claude credential lane and its delivery/revocation contract (SECRETS-WP-0009 upstream of CCR-2026-0016), owner machine authentication, the pinned Claude executable with its own HTTPS_PROXY startup proof, and the real-model acceptance run. Provider workspace scope and spend limit remain operator inputs; a model `budget_tokens` setting is not a provider spend limit. ## Pinned Claude candidate and isolated startup — 2026-09-06 The builder now accepts `--claude-binary`, `--claude-sha256` and `--claude-version` together. It requires a regular native ELF file, verifies the exact copied bytes, refuses symlinks/wrappers/mismatches and existing destination files, and copies only the executable as bin/claude mode 0755. The expected version is metadata until the sandbox smoke checks the actual output. No interactive HOME, provider key or login state is copied. Candidate provenance: the explicitly selected installed native release `/home/worsch/.local/share/claude/versions/2.1.263`, SHA-256 `26d020351e8112f4006790f3cfce43b4c9df0c1bb1d0e542364d64151b81d5ba`. This is a digest pin of the selected local artifact, not an upstream signature verification claim. Complete runtime candidate: `/tmp/sandboxer-claude-runtime-20260906`, SHA-256 `5cf9a16c5d77a16bdb2cb5b3df06ea655356bc2d44741791e3fedfee20d7e922`. Mount remains `/opt/sandboxer/runtime`; Claude is `/opt/sandboxer/runtime/bin/claude`. Rein sources remain 1429db5 / llm-connect 0056094; resolved dependency versions are recorded in the evidence. Rebuilding may resolve different dependencies; the complete digest pins this artifact, not future builds. Sandbox f8821ec2 ran real `claude --version` -> `2.1.263 (Claude Code)` plus rein CLI/import checks, with owner allowlisted provider egress and HTTPS_PROXY set by the broker. Runtime read-only, private 0700 HOME/state persistence, clean Git, absent source and loopback-only interfaces passed; workspace and proxy removed. `make check`: lint passed, 175 tests passed. Evidence: docs/evidence/SAND-WP-0015-claude-startup-2026-09-06.json. Reproduce with the builder options above and `scripts/smoke-bwrap-runtime.py --runtime-path --runtime-sha256 --claude-version 2.1.263`. Limits: `--version` proves startup with the proxy environment, not that Claude has sent a provider request through it. No credential acquisition or model run. The /tmp candidate is not production placement; protected artifact installation, owner configuration, credential adoption and real-model proof remain T04 gates.