chore(devcontainer): pre-seed known_hosts, install build-essentials (#10266)

.devcontainer/Dockerfile

@@ -1,6 +1,7 @@
 FROM ubuntu:26.04@sha256:cc925e589b7543b910fea57a240468940003fbfc0515245a495dd0ad8fe7cef1
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
+  build-essential \
   curl \
   default-jre \
   fd-find \
@@ -61,3 +62,11 @@ RUN chsh -s /bin/zsh root && \
     echo '[ -f /workspace/.devcontainer/zshrc ] && . /workspace/.devcontainer/zshrc' >> "$rc"; \
   done && \
   chown dev:dev /home/dev/.zshrc
+
+# Pre-seed GitHub's SSH host keys so git-over-SSH never prompts.  Keys are
+# pinned in-repo (verified against the fingerprints GitHub publishes at
+# https://docs.github.com/en/authentication/keeping-your-account-and-data-secure/githubs-ssh-key-fingerprints)
+# rather than fetched at build time, so a compromised build-time network can't
+# inject a rogue key.
+COPY github_known_hosts /etc/ssh/ssh_known_hosts
+RUN chmod 644 /etc/ssh/ssh_known_hosts

.devcontainer/devcontainer.json

@@ -1,7 +1,11 @@
 {
   "name": "Onyx Dev Sandbox",
-  "image": "onyxdotapp/onyx-devcontainer@sha256:0f02d9299928849c7b15f3b348dcfdcdcb64411ff7a4580cbc026a6ee7aa1554",
-  "runArgs": ["--cap-add=NET_ADMIN", "--cap-add=NET_RAW", "--network=onyx_default"],
+  "image": "onyxdotapp/onyx-devcontainer@sha256:4986c9252289b660ce772b45f0488b938fe425d8114245e96ef64b273b3fcee4",
+  "runArgs": [
+    "--cap-add=NET_ADMIN",
+    "--cap-add=NET_RAW",
+    "--network=onyx_default"
+  ],
   "mounts": [
     "source=${localEnv:HOME}/.claude,target=/home/dev/.claude,type=bind",
     "source=${localEnv:HOME}/.claude.json,target=/home/dev/.claude.json,type=bind",

.devcontainer/github_known_hosts

@@ -0,0 +1,3 @@
+github.com ssh-rsa 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
+github.com ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBEmKSENjQEezOmxkZMy7opKgwFB9nkt5YRrYMjNuG5N87uRgg6CLrbo5wAdT/y6v0mKV0U2w0WZ2YB/++Tpockg=
+github.com ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIOMqqnkVzrm0SdG6UOoqKLsabgH5C9okWi0dh2l9GKJl

.devcontainer/init-firewall.sh

@@ -4,6 +4,17 @@ set -euo pipefail
 
 echo "Setting up firewall..."
 
+# Reset default policies to ACCEPT before flushing rules.  On re-runs the
+# previous invocation's DROP policies are still in effect; flushing rules while
+# the default is DROP would block the DNS lookups below.  Register a trap so
+# that if the script exits before the DROP policies are re-applied at the end,
+# we fail closed instead of leaving the container with an unrestricted
+# firewall.
+trap 'iptables -P INPUT DROP; iptables -P OUTPUT DROP; iptables -P FORWARD DROP' EXIT
+iptables -P INPUT ACCEPT
+iptables -P OUTPUT ACCEPT
+iptables -P FORWARD ACCEPT
+
 # Only flush the filter table.  The nat and mangle tables are managed by Docker
 # (DNS DNAT to 127.0.0.11, container networking, etc.) and must not be touched —
 # flushing them breaks Docker's embedded DNS resolver.
@@ -34,8 +45,16 @@ ALLOWED_DOMAINS=(
     "pypi.org"
     "files.pythonhosted.org"
     "go.dev"
+    "proxy.golang.org"
+    "sum.golang.org"
     "storage.googleapis.com"
+    "dl.google.com"
     "static.rust-lang.org"
+    "index.crates.io"
+    "static.crates.io"
+    "archive.ubuntu.com"
+    "security.ubuntu.com"
+    "deb.nodesource.com"
 )
 
 for domain in "${ALLOWED_DOMAINS[@]}"; do

.pre-commit-config.yaml

@@ -141,6 +141,7 @@ repos:
     hooks:
       - id: ripsecrets
         args:
+          - --strict-ignore
           - --additional-pattern
           - ^sk-[A-Za-z0-9_\-]{20,}$
 

.secretsignore

@@ -0,0 +1 @@
+.devcontainer/github_known_hosts