fix(dashboard): allow configured reverse proxy hosts

[jeffery-zhang]

Summary

• allow loopback-bound dashboards to opt into trusted reverse-proxy hostnames via HERMES_DASHBOARD_ALLOWED_HOSTS
• keep the default DNS-rebinding Host/Origin rejection unchanged for unconfigured hosts
• add focused coverage for both the reject-by-default and configured-allowlist paths

Why

A dashboard can be safely exposed through a local reverse proxy or Cloudflare Tunnel while the FastAPI server remains bound to 127.0.0.1. In that setup, browser WebSocket requests use the public Host / Origin (for example https://dashboard.example.com), but the backend currently compares them only against the loopback bind host and rejects /api/pty and /api/events upgrades with origin_mismatch.

Binding the dashboard to 0.0.0.0 --insecure works around this, but it weakens the deployment by exposing the dashboard listener more broadly. This patch keeps the listener loopback-only and adds a narrow, explicit hostname allowlist for reverse-proxied deployments.

Testing

• python -m pytest tests/test_web_server.py -q
• python -m py_compile hermes_cli/web_server.py
• git diff --check

[alt-glitch]

Duplicate of #20136 — this implements the same dashboard reverse-proxy Host/Origin allowlist feature (here via HERMES_DASHBOARD_ALLOWED_HOSTS while keeping the loopback bind and default DNS-rebinding rejection). It joins a heavily saturated cluster: canonical #20136 (config-based, oldest open), with #27113 (env-var approach) and #28954 also open. Marking duplicate of the canonical; maintainer picks the mechanism.

[alt-glitch]

This was generated by AI during triage.

Correction to the earlier "Duplicate of #20136" note: #20136 is now closed, so this PR is no longer a duplicate of a closed item — the duplicate label has been removed. Re-classifying as related to the still-open, config-based competitor #47560 (dashboard.allowed_external_hosts), which solves the same reverse-proxy Host-header acceptance via a config key rather than this PR's HERMES_DASHBOARD_ALLOWED_HOSTS env var. Maintainer to pick one mechanism.

[Kinkoolino-Hermes]

Triage note after a fresh live + cross-PR check:

• This PR is still open, but currently has merge conflicts.
• The reverse-proxy Host/Origin cluster is still active. Relevant current neighbors I found: fix(dashboard): add Host allowlist for trusted reverse proxies #48954 is approved/mergeable and also uses HERMES_DASHBOARD_ALLOWED_HOSTS; feat(dashboard): configurable hostname allowlist for tunnel/proxy setups #47560 is the config-key variant (dashboard.allowed_external_hosts) but is also conflicting; fix(dashboard): trust configured public URL host #42344 uses the configured public URL host; [Bug]: Dashboard PTY/WebSocket fails behind reverse proxy after June 2026 dashboard security hardening #54072 is a related reverse-proxy/WebSocket issue that was closed after a user-side workaround.
• The distinct value of this PR is the small web_server.py + focused tests env-var allowlist path.

If maintainers want the env-var mechanism, the useful next step here is probably a rebase and an explicit comparison against #48954. If the preferred API is config-based instead, this may be superseded by #47560 or another config-surface PR.

[teknium1]

Thanks for the focused reverse-proxy analysis and regression coverage. The underlying loopback Host/Origin rejection is real, but this implementation uses a configuration surface we do not accept.

This automated hermes-sweeper review is closing this under the standing configuration policy:

• 9b286d5fda47 adds the user-facing non-secret setting HERMES_DASHBOARD_ALLOWED_HOSTS (hermes_cli/web_server.py:314).
• AGENTS.md:102-107 requires behavioral settings to live in config.yaml, rather than a new HERMES_* environment variable.
• Current dashboard configuration already uses the dashboard.* namespace (hermes_cli/config.py:2033-2053; website/docs/user-guide/features/web-dashboard.md:892-907).

A focused re-scope to a documented dashboard.* allowlist setting would be the supported path.

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Closed as not-planned per standing maintainer policy (env-var-for-config). This is a design-direction decision, not a code-quality judgment — see the Contribution Rubric in AGENTS.md for what the project is looking for. If you believe this policy was misapplied to your change, comment here and a maintainer will take a look.