fix(container): APP_HOST defaults to 127.0.0.1 (HCG tier-2 E1 prereq)

[hyperpolymath]

Summary

Tightens three sites that feed the Zig adapter binary's --host flag in production deployments, materialising the ADR-0004 §1 invariant that BoJ's back-side bind is not externally routable when fronted by http-capability-gateway (HCG tier-2).

This is action item #7 from the Phase E consumer-side audit. The scope expanded during implementation from one site (the audit named stapeln.toml) to three sites — entrypoint.sh and compose.prod.yaml had the same [::] default that the audit missed. All three sites feed into the same Zig-adapter --host flag, so they need to flip together for the change to actually take effect at runtime.

Companion PR to #130 (Cowboy bind tightening in the Elixir path) and #131 (k8s Service ClusterIP). Together the three give defence in depth: Elixir Cowboy binds loopback AND Zig adapter binds loopback AND k8s Service is internal-only.

Refs hyperpolymath/standards#100 (NOT Closes — joint-close is owner-only).
Refs hyperpolymath/standards#91.

What's in

File	Change
stapeln.toml [targets.production]	APP_HOST = "[::]" → APP_HOST = "127.0.0.1" + comment block.
container/entrypoint.sh line 40 (log) + line 140 (exec invocation)	${APP_HOST:-[::]} → ${APP_HOST:-127.0.0.1} + comment at exec line.
container/compose.prod.yaml services.boj-rest.environment	APP_HOST: "[::]" → APP_HOST: "127.0.0.1" + comment block.
CHANGELOG.md	New ### Changed entry under [Unreleased].

Override path for legacy/standalone use

Deployments without HCG in front: set APP_HOST=0.0.0.0 (IPv4 all-interfaces) or APP_HOST=:: (IPv6 all-interfaces) in your deployment config. The in-repo defaults remain loopback.

Audit-residue follow-ups deliberately NOT in this PR

• container/Containerfile line 125: ENV PHX_HOST=0.0.0.0 is vestigial. Nothing in the codebase reads PHX_HOST (verified by grep -rn "PHX_HOST\|phx_host" --include="*.ex" ... returning empty). Leftover from a former Phoenix incarnation. Safe to leave alone; can be removed in a hygiene PR if desired.
• Unifying APP_HOST (Zig adapter) and BOJ_BIND_IP (Elixir Cowboy from fix(boj): bind Cowboy to 127.0.0.1 by default (HCG tier-2 E1 prereq) #130) into one envelope is broader scope. The divergence exists because they feed different binaries built by different toolchains. If it proves annoying in operation, file a separate issue.

Why DRAFT

Same reason as #131 — this is a behaviour change for anyone running the stapeln-built production container or compose.prod.yaml as-is and relying on the default [::] for external access. Owner gates merge on confirming no such reliance, or on coordinating with anyone who needs the migration path (HCG-in-front, or explicit APP_HOST=0.0.0.0 override).

Test plan

• stapeln.toml parses as valid TOML (syntax preserved).
• container/entrypoint.sh runs through sh -n without syntax error (no syntax change, just literal substitution).
• container/compose.prod.yaml parses as valid YAML.
• CI green — governance / hypatia / a2ml / k9 / dogfooding all pass.
• Owner: confirm no live deployment depends on [::] default; flip from DRAFT to ready.
• Post-merge manual: a stapeln-built production container, with no env override, refuses connections from non-loopback peers.

Risk

Low for the codebase, medium for ops. No Elixir / Zig / Idris2 / cartridge logic touched; CI should not show any regressions. Ops risk: anyone whose runbook assumes the container exposes BoJ on all interfaces by default will need to set APP_HOST=0.0.0.0 explicitly. Reasonable default for the Phase E posture; documented override path.

🤖 Generated with Claude Code

[hyperpolymath]

CI auto-trigger anomaly — manual dispatch worked

PR-triggered workflows did not fire on this branch (no pull_request events for either the initial push bda043dc or the no-op empty commit e44b2799). Close+reopen and ready-flip also failed to re-trigger. Other PRs opened in this session (#130, #131) and other sessions (#129) got their checks normally.

Hypothesis: estate-wide CI concurrency-pool saturation from the active sweep122 campaign ([memory: project_ci_concurrency_pool_estate]) — Terminal-7 launched at 09:33Z (PID 244005) is opening dup PRs across ~297 repos. The workflow_dispatch code path still works.

Manual dispatch result for Governance (the most relevant check given the file types in this PR — TOML + shell + YAML): all 6 jobs green at https://github.com/hyperpolymath/boj-server/actions/runs/26156354986

• ✓ Security policy checks
• ✓ Well-Known (RFC 9116 + RSR)
• ✓ Guix primary / Nix fallback policy
• ✓ Code quality + docs
• ✓ Language / package anti-pattern policy
• ✓ Workflow security linter

Other workflows (Dogfood Gate, CodeQL, Secret Scanner) don't support workflow_dispatch and so can't be manually triggered. Suggest the owner either (a) waits for the concurrency pool to free up and re-runs via the Actions tab, or (b) merges the v2 branch superseded earlier if checks resume; my PR's content is safe to land without CodeQL+Secret-Scanner+Dogfood since the diff is configuration-only (TOML + shell ${VAR:-default} substitution + YAML).

Leaving the PR DRAFT until checks land.

🤖 Generated with Claude Code

[github-actions]

🔍 Hypatia Security Scan

Findings: 30 issues detected

Severity	Count
🔴 Critical	18
🟠 High	5
🟡 Medium	7

⚠️ Action Required: Critical security issues found!

View findings

[
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    "type": "stale",
    "file": "GEMINI.md",
    "action": "delete",
    "rule_module": "root_hygiene",
    "severity": "medium"
  },
  {
    "reason": "Issue in quality.yml",
    "type": "missing_workflow",
    "file": "quality.yml",
    "action": "create",
    "rule_module": "workflow_audit",
    "severity": "high"
  },
  {
    "reason": "Issue in security-policy.yml",
    "type": "missing_workflow",
    "file": "security-policy.yml",
    "action": "create",
    "rule_module": "workflow_audit",
    "severity": "medium"
  },
  {
    "reason": "Action hyperpolymath/standards/.github/workflows/governance-reusable.yml@main needs attention",
    "type": "unpinned_action",
    "file": "governance.yml",
    "action": "pin_sha",
    "rule_module": "workflow_audit",
    "severity": "high"
  },
  {
    "reason": "TypeScript file detected -- banned language",
    "type": "banned_language_file",
    "file": "/home/runner/work/boj-server/boj-server/cartridges/sanctify-mcp/adapter/mod.ts",
    "action": "flag",
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    "severity": "critical"
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  {
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    "action": "flag",
    "rule_module": "cicd_rules",
    "severity": "critical"
  },
  {
    "reason": "TypeScript file detected -- banned language",
    "type": "banned_language_file",
    "file": "/home/runner/work/boj-server/boj-server/cartridges/bofig-mcp/adapter/mod.ts",
    "action": "flag",
    "rule_module": "cicd_rules",
    "severity": "critical"
  },
  {
    "reason": "TypeScript file detected -- banned language",
    "type": "banned_language_file",
    "file": "/home/runner/work/boj-server/boj-server/cartridges/hesiod-mcp/adapter/mod.ts",
    "action": "flag",
    "rule_module": "cicd_rules",
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]

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