diff --git a/.github/workflows/boot-init.yml b/.github/workflows/boot-init.yml
index 2c834f44..59631a4e 100644
--- a/.github/workflows/boot-init.yml
+++ b/.github/workflows/boot-init.yml
@@ -8,6 +8,7 @@ on:
     branches: [main]
     paths:
       - "boot/init/**"
+      - ".github/workflows/boot-init.yml"
   pull_request:
     paths:
       - "boot/init/**"
@@ -27,5 +28,5 @@ jobs:
         working-directory: boot/init
         run: |
           cargo fmt --check
-          cargo clippy --all-targets -- -D warnings
-          cargo test
+          cargo clippy --locked --all-targets -- -D warnings
+          cargo test --locked
diff --git a/.github/workflows/build-boot.yml b/.github/workflows/build-boot.yml
index 17d9b8a1..6037132c 100644
--- a/.github/workflows/build-boot.yml
+++ b/.github/workflows/build-boot.yml
@@ -38,8 +38,8 @@ jobs:
         working-directory: boot/init
         run: |
           cargo fmt --check
-          cargo clippy --all-targets -- -D warnings
-          cargo test
+          cargo clippy --locked --all-targets -- -D warnings
+          cargo test --locked
 
   build:
     needs: test
diff --git a/.github/workflows/build-os-images.yml b/.github/workflows/build-os-images.yml
index 99fd6b43..c566c451 100644
--- a/.github/workflows/build-os-images.yml
+++ b/.github/workflows/build-os-images.yml
@@ -76,9 +76,12 @@ jobs:
           }
 
           # A changed carrier (boot/silkd) refolds into every image; a manual
-          # run or a first push (no BEFORE) rebuilds all. Otherwise only the
-          # git-changed image dirs rebuild.
-          if [[ "$CARRIER_CHANGED" == "true" || "$MANUAL" == "true" || "$BEFORE" == "0000000000000000000000000000000000000000" ]]; then
+          # run, a first push (no BEFORE), or a change to how the images are
+          # built rebuilds all. Otherwise only the git-changed image dirs
+          # rebuild. The workflow diff is last so a manual run never runs git.
+          wf=.github/workflows
+          if [[ "$CARRIER_CHANGED" == "true" || "$MANUAL" == "true" || "$BEFORE" == "0000000000000000000000000000000000000000" ]] ||
+             git diff --name-only "$BEFORE" "$SHA" -- "$wf/build-os-images.yml" "$wf/images.yml" | grep -q .; then
             all_names
             all_changed=""
           else
@@ -109,7 +112,7 @@ jobs:
               needs_no_cache="true"
             elif [[ -n "$all_changed" ]]; then
               while IFS= read -r f; do
-                [[ -z "$f" ]] && continue
+                [[ -z "$f" || "$f" == *.md ]] && continue
                 depth=$(echo "$f" | awk -F'/' '{print NF}')
                 base_name=$(basename "$f")
                 if [[ "$depth" -eq 3 ]] || { [[ "$depth" -eq 4 ]] && [[ "$base_name" != "Dockerfile" ]]; }; then
@@ -195,7 +198,7 @@ jobs:
       - name: Hash image inputs
         id: inputs
         run: |
-          hash=$(find "os-image/${{ matrix.name }}" -type f ! -name Dockerfile -print0 | sort -z | xargs -0 sha256sum | sha256sum | cut -d' ' -f1)
+          hash=$(find "os-image/${{ matrix.name }}" -type f ! -name Dockerfile ! -name '*.md' -print0 | sort -z | xargs -0 sha256sum | sha256sum | cut -d' ' -f1)
           echo "hash=$hash" >> "$GITHUB_OUTPUT"
 
       - name: Discover secret files
@@ -286,7 +289,7 @@ jobs:
       - name: Hash image inputs
         id: inputs
         run: |
-          hash=$(find "os-image/${{ matrix.name }}" -type f ! -name Dockerfile -print0 | sort -z | xargs -0 sha256sum | sha256sum | cut -d' ' -f1)
+          hash=$(find "os-image/${{ matrix.name }}" -type f ! -name Dockerfile ! -name '*.md' -print0 | sort -z | xargs -0 sha256sum | sha256sum | cut -d' ' -f1)
           echo "hash=$hash" >> "$GITHUB_OUTPUT"
 
       - name: Discover secret files
diff --git a/.github/workflows/build-silkd.yml b/.github/workflows/build-silkd.yml
index 27d6d644..fcde41a1 100644
--- a/.github/workflows/build-silkd.yml
+++ b/.github/workflows/build-silkd.yml
@@ -34,8 +34,8 @@ jobs:
         working-directory: silkd
         run: |
           cargo fmt --check
-          cargo clippy --all-targets -- -D warnings
-          cargo test
+          cargo clippy --locked --all-targets -- -D warnings
+          cargo test --locked
 
   build:
     needs: test
diff --git a/.github/workflows/images.yml b/.github/workflows/images.yml
index 7ba5a3aa..312bc82a 100644
--- a/.github/workflows/images.yml
+++ b/.github/workflows/images.yml
@@ -15,6 +15,10 @@ on:
       - "silkd/**"
       - "protocol/**"
       - "os-image/**"
+      - ".github/workflows/images.yml"
+      - ".github/workflows/build-os-images.yml"
+      - ".github/workflows/build-silkd.yml"
+      - ".github/workflows/build-boot.yml"
   workflow_dispatch:
     inputs:
       no-cache:
@@ -55,9 +59,12 @@ jobs:
             boot=true; silkd=true; osimage=true
           else
             changed() { git diff --name-only "$BEFORE" "$SHA" -- "$@" | grep -q .; }
-            changed boot/ && boot=true || boot=false
-            changed silkd/ protocol/ && silkd=true || silkd=false
-            changed os-image/ && osimage=true || osimage=false
+            # Each area carries its own build workflow: changing how an image is
+            # built must rebuild it, or the run goes green having built nothing.
+            wf=.github/workflows
+            changed boot/ $wf/build-boot.yml && boot=true || boot=false
+            changed silkd/ protocol/ $wf/build-silkd.yml && silkd=true || silkd=false
+            changed os-image/ $wf/build-os-images.yml $wf/images.yml && osimage=true || osimage=false
           fi
           {
             echo "boot=$boot"
diff --git a/.github/workflows/publish-pypi.yml b/.github/workflows/publish-pypi.yml
index 95c46158..f0812f54 100644
--- a/.github/workflows/publish-pypi.yml
+++ b/.github/workflows/publish-pypi.yml
@@ -58,7 +58,7 @@ jobs:
           # The in-repo base SDK installs first, so an adapter release never
           # resolves (or fails to resolve) cocoonstack-sandbox from PyPI.
           python -m pip install -q ./sdk/python
-          python -m pip install -q "${{ steps.pkg.outputs.dir }}" pytest ruff
+          python -m pip install -q "${{ steps.pkg.outputs.dir }}" ruff==0.15.20 pytest==8.4.2
           (cd "${{ steps.pkg.outputs.dir }}" && ruff check . && python -m pytest -q)
 
       - name: Build sdist + wheel
diff --git a/.github/workflows/python.yml b/.github/workflows/python.yml
index 6ee70b0c..4effbbe4 100644
--- a/.github/workflows/python.yml
+++ b/.github/workflows/python.yml
@@ -2,6 +2,7 @@ name: python
 
 on:
   push:
+    branches: [main]
     paths:
       - "sdk/python/**"
       - "sdk/openai/**"
@@ -20,6 +21,8 @@ on:
       - "e2e/**/*.py"
       - "ruff.toml"
       - "protocol/**"
+      - ".github/workflows/python.yml"
+  workflow_dispatch:
 
 jobs:
   test:
diff --git a/.github/workflows/silkd.yml b/.github/workflows/silkd.yml
index 4ed2ecc8..849cff73 100644
--- a/.github/workflows/silkd.yml
+++ b/.github/workflows/silkd.yml
@@ -9,6 +9,7 @@ on:
     paths:
       - "silkd/**"
       - "protocol/**"
+      - ".github/workflows/silkd.yml"
   pull_request:
     paths:
       - "silkd/**"
@@ -29,5 +30,5 @@ jobs:
         working-directory: silkd
         run: |
           cargo fmt --check
-          cargo clippy --all-targets -- -D warnings
-          cargo test
+          cargo clippy --locked --all-targets -- -D warnings
+          cargo test --locked
diff --git a/Makefile b/Makefile
index d55553c3..c4dabce9 100644
--- a/Makefile
+++ b/Makefile
@@ -91,6 +91,7 @@ base: silkd-image ## base VM image against the local boot + silkd images
 	docker build -t sandbox-base:dev \
 		--build-arg BOOT_IMAGE=$(BOOT_IMAGE) \
 		--build-arg SILKD_IMAGE=$(SILKD_IMAGE) \
+		--build-arg INPUTS_HASH=$$(find os-image/base -type f ! -name Dockerfile -print0 | sort -z | xargs -0 shasum -a 256 | shasum -a 256 | cut -d' ' -f1) \
 		--secret id=sandbox_install_agent,src=os-image/base/install-agent.sh \
 		-f os-image/base/24.04/Dockerfile os-image/base
 
@@ -99,4 +100,4 @@ python: base ## python flavor image on top of base
 		--build-arg BASE_IMAGE=sandbox-base:dev \
 		-f os-image/python/3.12/Dockerfile os-image/python
 
-images: base python ## all VM images
+images: base python ## the local base and python images (CI builds every flavor)
diff --git a/README.md b/README.md
index 79deb737..b9385c17 100644
--- a/README.md
+++ b/README.md
@@ -58,8 +58,8 @@ performance) — source in
   cocoon+guest) plus bare-metal acceptance drivers under `cmd/`: `demo`,
   `smoke`, `meshsmoke`, `crossnode`, `coldproof`, `egresssmoke`,
   `interceptsmoke`, `sockssmoke`, `volumesmoke`, `lifecycle` (idle→hibernate→archive),
-  `androidsmoke`, `browsersmoke`, `desktopsmoke`, and the `pullbench`/`pushbench`/`rpcbench`/`qaab`
-  perf drivers
+  `androidsmoke`, `browsersmoke`, `desktopsmoke`, `ringsmoke` (output ring cap, exec as a user),
+  and the `pullbench`/`pushbench`/`rpcbench`/`qaab` perf drivers
 - `boot/kernel/` — kernel version pin (`VERSION` + matching tarball `SHA256`,
   bump both together) + config fragment (amd64: over `x86_64_defconfig` +
   `kvm_guest.config`; arm64: over `defconfig`, then `sandbox-arm64.config`)
@@ -159,6 +159,11 @@ Boot contract (cmdline keys consumed by sandbox-init):
 | `sandbox.debug=1` | fatal errors drop to `/bin/sh` (debug initramfs) instead of poweroff |
 | `sandbox.trace=1` | emit one pre-handoff line with per-phase µs timings |
 
+The pinned kernel builds no 8250 UART, so on cocoon's Firecracker lane
+(`console=ttyS0`) the trace line, the debug shell and the fatal-error
+message all go nowhere; they are visible on the Cloud Hypervisor lane's
+virtio console.
+
 `boot=cocoon-overlay` is ignored. Everything cocoon passes today keeps
 working — images built here boot with an unmodified cocoon.
 
diff --git a/boot/Dockerfile b/boot/Dockerfile
index 1720e9c3..c24c27c1 100644
--- a/boot/Dockerfile
+++ b/boot/Dockerfile
@@ -46,7 +46,7 @@ RUN set -e; \
     case "$TARGETARCH" in \
       amd64) make x86_64_defconfig kvm_guest.config; \
              ./scripts/kconfig/merge_config.sh -m .config /tmp/sandbox.config; \
-             arch_asserts="PVH VIRTIO_CONSOLE" ;; \
+             arch_asserts="PVH" ;; \
       arm64) make defconfig; \
              ./scripts/kconfig/merge_config.sh -m .config /tmp/sandbox.config /tmp/sandbox-arm64.config; \
              arch_asserts="RTC_DRV_PL031" ;; \
diff --git a/docs/sdk-python.md b/docs/sdk-python.md
index ec92e265..121cdf0b 100644
--- a/docs/sdk-python.md
+++ b/docs/sdk-python.md
@@ -498,9 +498,11 @@ zero.
 - `APIError(verb, status, message)` — control plane (HTTP status)
 - `SilkdError(kind, message)` — typed guest failure; `kind` is
   `bad_request` (including a spawn the guest cannot start: missing binary, a
-  cwd that is not a directory, no exec bit) / `not_found` / `unimplemented` /
-  `internal`
+  cwd that is not a directory, no exec bit, a `user` the guest cannot
+  resolve) / `not_found` / `unimplemented` / `internal`
 - `ExitError(code, stderr, stdout)` — non-zero exit from `exec`
+- `SandboxTimeout` — a caller's timeout or deadline expired before the call
+  finished; also a `TimeoutError`
 - `ProtocolError` — a failed relay dial or TLS handshake, or a broken stream
   (EOF, oversized or undecodable frame)
 
diff --git a/docs/sdk.md b/docs/sdk.md
index 1b5e5242..95cb8e44 100644
--- a/docs/sdk.md
+++ b/docs/sdk.md
@@ -629,7 +629,8 @@ claims; the fields are those of [`GET /v1/sandboxes`](sandboxd-api.md#get-v1sand
 - `*sandbox.ExitError` — non-zero exit from `Exec` (`Code`, `Stderr`)
 - `*wire.ErrorResp` — a typed guest-side failure; `Kind` is one of
   `wire.KindBadRequest` (including a spawn the guest cannot start: missing
-  binary, a cwd that is not a directory, no exec bit), `KindNotFound`,
+  binary, a cwd that is not a directory, no exec bit, a `User` the guest
+  cannot resolve), `KindNotFound`,
   `KindUnimplemented`, `KindInternal` (import
   `github.com/cocoonstack/sandbox/protocol/wire`)
 
diff --git a/docs/silkd.md b/docs/silkd.md
index 145fbdec..bca3387e 100644
--- a/docs/silkd.md
+++ b/docs/silkd.md
@@ -61,7 +61,7 @@ A failed verb terminates with `error {kind, message}`:
 
 | kind | meaning |
 |---|---|
-| `bad_request` | malformed frame, empty argv, invalid pattern, an exec argv or cwd the guest cannot spawn (missing, not a directory, not executable) |
+| `bad_request` | malformed frame, empty argv, invalid pattern, an exec argv or cwd the guest cannot spawn (missing, not a directory, not executable), an exec or pty `user` the guest cannot resolve (`unknown user`, or `look up user: <errno>` when the name service itself fails) |
 | `not_found` | unknown pid/session/path, a `port_forward` port nothing listens on, a language with no LSP manifest |
 | `unimplemented` | verb unavailable on this lane — notably git clone/push/pull on the no-network lane, whose message points at `fs.push` |
 | `internal` | everything else (other spawn failures, git errors, I/O) |
diff --git a/os-image/android/silkd.rc b/os-image/android/silkd.rc
index 0028d1e1..e508fe56 100644
--- a/os-image/android/silkd.rc
+++ b/os-image/android/silkd.rc
@@ -10,6 +10,7 @@ service silkd /system/bin/silkd
     user root
     group root
     setenv SILKD_PORT 2048
+    setenv SHELL /system/bin/sh
     # Mirrors the base:24.04 unit; forwarded into execs only on the no-NIC lane.
     setenv http_proxy http://127.0.0.1:3128
     setenv https_proxy http://127.0.0.1:3128
diff --git a/os-image/desktop/24.04/Dockerfile b/os-image/desktop/24.04/Dockerfile
index 5d4cc481..9b448fc0 100644
--- a/os-image/desktop/24.04/Dockerfile
+++ b/os-image/desktop/24.04/Dockerfile
@@ -44,7 +44,7 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
     && install -d -m 0755 /etc/apt/keyrings \
     && curl -fsSL https://dl.google.com/linux/linux_signing_key.pub \
       | gpg --dearmor -o /etc/apt/keyrings/google-chrome.gpg \
-    && echo "deb [arch=amd64 signed-by=/etc/apt/keyrings/google-chrome.gpg] http://dl.google.com/linux/chrome/deb/ stable main" \
+    && echo "deb [arch=amd64 signed-by=/etc/apt/keyrings/google-chrome.gpg] https://dl.google.com/linux/chrome/deb/ stable main" \
       > /etc/apt/sources.list.d/google-chrome.list \
     && apt-get update && apt-get install -y --no-install-recommends google-chrome-stable \
     && rm -rf /var/lib/apt/lists/* \
diff --git a/scripts/bench.sh b/scripts/bench.sh
index 76a9a676..fb44f0c2 100755
--- a/scripts/bench.sh
+++ b/scripts/bench.sh
@@ -169,7 +169,7 @@ done
 virt=$(systemd-detect-virt 2>/dev/null || true); virt=${virt:-unknown}
 [[ $virt == none ]] && envlabel="bare metal" || envlabel="nested ($virt)"
 cpu=$(awk -F': ' '/model name/{print $2; exit}' /proc/cpuinfo 2>/dev/null || sysctl -n machdep.cpu.brand_string 2>/dev/null || echo unknown)
-digest=$(cocoon image list 2>/dev/null | awk -v t="$TEMPLATE" '$2 ~ t {print $3; exit}')
+digest=$(cocoon image list 2>/dev/null | awk -v t="$TEMPLATE" '$2 ~ t {print $3; exit}' || true)
 
 echo
 echo "== results (paste into docs/benchmarks.md)"
diff --git a/sdk/python/cocoonsandbox/conn.py b/sdk/python/cocoonsandbox/conn.py
index a8018a2d..0dc4a264 100644
--- a/sdk/python/cocoonsandbox/conn.py
+++ b/sdk/python/cocoonsandbox/conn.py
@@ -57,7 +57,7 @@ def recv(self) -> dict[str, Any]:
         """Reads one frame or raises a typed protocol or guest error."""
         try:
             line = self._reader.readline(MAX_FRAME + 1)
-        except OSError as exc:
+        except (OSError, ValueError) as exc:
             raise ProtocolError(f"read failed: {exc}") from exc
         if not line:
             raise ProtocolError("connection closed mid-stream")
@@ -159,6 +159,8 @@ def dial_agent(
     ssl_context: ssl.SSLContext | None = None,
 ) -> Conn:
     """Opens one TCP/HTTP Upgrade relay within timeout and the optional deadline."""
+    budget = time.monotonic() + timeout
+    deadline = budget if deadline is None else min(deadline, budget)
     for name, value in (("sandbox id", sandbox_id), ("token", token)):
         if any(c in value for c in "\r\n\0"):
             raise APIError("agent upgrade", 0, f"{name} contains a control character")
diff --git a/sdk/python/cocoonsandbox/frames.py b/sdk/python/cocoonsandbox/frames.py
index 64dd4aa6..137bec13 100644
--- a/sdk/python/cocoonsandbox/frames.py
+++ b/sdk/python/cocoonsandbox/frames.py
@@ -5,6 +5,7 @@
 import base64
 import binascii
 import json
+import sys
 from typing import Any
 
 PROTO_VERSION = 1
@@ -14,6 +15,7 @@
 FS_CHUNK = 256 * 1024
 # tar and port streams chunk at 1 MiB: fewer frames per byte, still under MAX_FRAME after base64
 BULK_CHUNK = 1 << 20
+_FAST_DATA = sys.version_info >= (3, 11)
 
 
 def encode_request(op: str, **fields: object) -> bytes:
@@ -34,7 +36,7 @@ def encode_request(op: str, **fields: object) -> bytes:
 def decode_response(line: bytes) -> dict[str, Any]:
     """Decodes one response with binary payloads under data."""
     # base64 is JSON-escape-free, so an exactly-shaped data frame slices without json.loads.
-    if line.startswith(b'{"type":"'):
+    if _FAST_DATA and line.startswith(b'{"type":"'):
         te = line.find(b'"', 9)
         if te > 0 and line[9:te] in (b"stdout", b"stderr", b"data") and line.startswith(b'","data":"', te):
             de = line.find(b'"', te + 10)
diff --git a/sdk/python/tests/test_hardening.py b/sdk/python/tests/test_hardening.py
index c2a97b2f..c0275a35 100644
--- a/sdk/python/tests/test_hardening.py
+++ b/sdk/python/tests/test_hardening.py
@@ -9,7 +9,18 @@
 import pytest
 from conftest import sandbox_at
 
-from cocoonsandbox import APIError, Client, Lsp, ProtocolError, Pty, SandboxError, Session, SilkdError, Watcher
+from cocoonsandbox import (
+    APIError,
+    Client,
+    Lsp,
+    ProtocolError,
+    Pty,
+    SandboxError,
+    SandboxTimeout,
+    Session,
+    SilkdError,
+    Watcher,
+)
 from cocoonsandbox.conn import Conn, dial_agent, remaining_timeout
 from cocoonsandbox.frames import FS_CHUNK
 
@@ -151,3 +162,39 @@ def test_sandbox_timeout_is_both_hierarchies():
         remaining_timeout(1.0, time.monotonic() - 1, "probe")
     with pytest.raises(TimeoutError):
         remaining_timeout(1.0, time.monotonic() - 1, "probe")
+
+
+def test_recv_after_close_is_a_protocol_error() -> None:
+    a, b = socket.socketpair()
+    conn = Conn(a, a.makefile("rb"))
+    conn.close()
+    b.close()
+    with pytest.raises(ProtocolError):
+        conn.recv()
+
+
+def test_dial_timeout_bounds_the_whole_upgrade() -> None:
+    server = socket.socket()
+    server.bind(("127.0.0.1", 0))
+    server.listen(1)
+
+    def slow_headers() -> None:
+        peer, _ = server.accept()
+        peer.sendall(b"HTTP/1.1 101 Switching Protocols\r\n")
+        for n in range(8):
+            time.sleep(0.15)
+            try:
+                peer.sendall(f"X-Slow-{n}: 1\r\n".encode())
+            except OSError:
+                break
+        peer.close()
+
+    threading.Thread(target=slow_headers, daemon=True).start()
+    addr = f"127.0.0.1:{server.getsockname()[1]}"
+    started = time.monotonic()
+    with pytest.raises(SandboxTimeout):
+        dial_agent(addr, "sb_x", "tok", timeout=0.2)
+    assert time.monotonic() - started < 0.6, (
+        "each header arrived under the per-read timeout; only a whole-dial budget stops this"
+    )
+    server.close()