✨ backends: add openhands as a T3 headless-only contributor backend

[clubanderson]

Summary

• Adds openhands (OpenHands CLI, PyPI openhands, MIT) as a T3 experimental, headless-only contributor backend, following src/docs/backend-support-tiers.md.
• Relay dispatch: openhands --headless -t "<prompt>" --always-approve --override-with-envs. --override-with-envs is required because the CLI otherwise ignores LLM_API_KEY/LLM_BASE_URL/LLM_MODEL in favour of ~/.openhands/settings.json; OpenHands has no --model flag, so AGENT_MODEL is forwarded as LLM_MODEL (new headlessChildEnv() in the relay, openhands added to NO_MODEL_FLAG_BACKENDS).
• Refusal gate HIVE_OPENHANDS_DANGEROUSLY_RUN_UNCONFINED (Default agent launch path is unconfined on the operator's host — an agent running an assigned repo's test suite reached my bootloader #4918 contract), honest detect_cli (probes LLM_API_KEY / settings.json; --version is an argparse version action that exits 0 with no credential), Justfile preflight, Go CLIBackends + teams label, posture table + backends.conf comment guard, docs rows, changelog fragment.
• Context: part of the ecosystem/visibility push alongside ✨ landscape: GitHub Agentic Workflows (gh-aw) on-ramp + agentics gallery entry #10625, 📝 landscape: OpenAI Symphony positioning and SPEC.md alignment review #10626, 🌱 ecosystem: Goose upstream docs and repo-move verification #10627. Note upstream has marked the OpenHands-CLI repo as no longer actively maintained (in favour of Agent Canvas); the CLI is still published (1.16.0) — stated plainly in the docs rows.

Related issues

Refs #6231 (backend acceptance bar). Related: #10625 #10626 #10627

Tier claimed

• pod path: not claimed — openhands stays out of HEADLESS_BACKENDS / K8S_HEADLESS_BACKENDS; not installed in src/Dockerfile.contributor (image is bookworm/Python 3.11, OpenHands needs 3.12 — follow-up if wanted, with a pinned uv + uv tool install openhands==<ver>).
• local path: T3 — refusal-gated (postureRefusalGated).

Safety flags

• backend_perm_flag openhands → --always-approve --override-with-envs (verified: bash -c 'source config/backends.conf; backend_perm_flag openhands').
• Both are argparse store_true flags (no value to be misparsed). --always-approve is mutually exclusive with --llm-approve (argparse group → exit 2 if both). --headless without -t/-f → parser.error → exit 2, so a mis-built argv fails loudly rather than opening the TUI. Headless mode forces always-approve regardless (docs.openhands.dev/openhands/usage/cli/headless). Source: OpenHands/OpenHands-CLI openhands_cli/entrypoint.py, argparsers/util.py.
• Refusal gate verified: unconfined_local_perm_flag_shell openhands exits 1 without the env var, emits the flags with HIVE_OPENHANDS_DANGEROUSLY_RUN_UNCONFINED=1.

Metering posture

Unmetered on this path (OpenHands reports usage to its own conversation store, not to hive's sinks). Budget-gated hives should treat it as unmetered — same as the other T3 relay-only CLIs.

Testing

• node bin/contributor-relay.test.js: 600/680 (baseline on this macOS host: 598/678 — the 80 failures are pre-existing tmux/env-dependent; the 2 new openhands tests pass).
• go test ./pkg/config/ ok; go test ./pkg/agent/ -run Backend ok.
• go test ./pkg/dashboard/ — all backend/local-mode/matrix/teams tests pass. Two unrelated failures (TestAgentsCollapsedSummaryRendersPerAgentTiles, TestOpenAPISpecCoversEveryRegisteredRoute) reproduce identically on untouched v5 HEAD. Heads-up: pkg/dashboard currently panics at init on v5 HEAD (feedback.go:80 uses a (?= lookahead Go's regexp rejects — from 🐛 feedback: attribute dashboard feedback issues to the submitter #10593); I patched it locally only to run the suite and did not include that change.
• bash -n on backends.conf / contributor-agent.sh; just --summary parses.

Adding or changing a CLI backend?

• PR body states the claimed tier per launch path (pod / local).
• List parity: KNOWN_BACKENDS, backend_binary, backend_perm_flag, config.CLIBackends (TestShellAndGoCLIBackendListsAgree passes).
• Local posture declared and tested (localBackendPostures["openhands"] = postureRefusalGated; unconfined_local_backend_env_var; comment guard string updated).
• Safety flags honored: see above.
• Credential detection is honest (detect_cli probes LLM_API_KEY or settings.json, not --version alone).
• Docs rows: docs/backend-setup.md, src/docs/sandbox-isolation.md, src/docs/contributor-relay.md (AGENT_BACKEND, env var, instruction-file, backend table rows).
• Installs pinned: n/a — not added to any image.
• Metering posture stated.

Contributor checklist

• Changelog fragment changelog.d/added-openhands-backend.md
• Targets v5
• Emoji title
• DCO sign-off
• Docs updated
• No secrets committed

[kubestellar-prow]

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[github-actions]

Open PR overlap check

Base branch: v5

Conflicts are checked with every PR merged onto the current tip of v5, so a PR that only needs a rebase is not reported as conflicting with its siblings.

PR	Title	Relation	Files
#10636	📖 docs: align Goose integration with AAIF upstream	same files	config/backends.conf docs/backend-setup.md

[hivecommons-hive]

Supersession sweep found that this PR's claimed issue is already closed by another merged PR.

• Claimed issue: hive#6231
• Closing PR: #6299

A different merged PR closed the claimed issue. Leaving this contributor PR open for a human to review.

This comment is edited in place by the supersession sweep; it is not duplicated.

[clubanderson]

CI note: the remaining red jobs are the pre-existing v5 baseline failures, each reproduced on untouched origin/v5 HEAD (0904d04) with no change from this PR:

• TestAgentsCollapsedSummaryRendersPerAgentTiles and TestOpenAPISpecCoversEveryRegisteredRoute (pkg/dashboard)
• TestStyleRatchet (pkg/dashboard/webstatic — static/index.html raw-padding 230 > baseline 229; this PR does not touch index.html)

Everything this PR touches is green: backend parity/posture tests, pkg/config, pkg/hub, relay JS tests, docs link/citation checks, lint, build. Rebased onto #10617 so the earlier hub/dashboard init panic is gone.

[github-actions]

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