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+# Handoff — brainstorm deployment responsibility (left4me vs. ckn-bw)
+
+## Status
+
+Queued for a future session, **after the uid-collapse refactor lands**
+(`docs/superpowers/plans/2026-05-15-uid-collapse.md`). This is a
+framing doc for a brainstorming session, not an implementation plan.
+The brainstorming session should use `superpowers:brainstorming` and
+exit with a design doc; implementation follows separately.
+
+## The question
+
+How should left4me and ckn-bw split responsibility for the host's
+deployment?
+
+**Not a fresh question.** The original deployment design at
+`docs/superpowers/specs/2026-05-06-left4me-deployment-design.md`
+already laid out the canonical shape: `deploy/files/` in the left4me
+repo mirrors target filesystem paths for root-owned deployment
+artifacts (systemd units, sudoers, helpers, env templates);
+"production config management can own both env files directly"
+(line 91). The implicit model: **left4me defines the deployment
+artifacts; ckn-bw integrates them onto the host.** That spec also
+defined a self-contained `deploy/deploy-test-server.sh` so the
+deployment could be exercised without ckn-bw at all.
+
+Over time, more and more of those artifacts migrated *into* ckn-bw's
+`bundles/left4me/` — specifically:
+- systemd unit definitions are now emitted by the
+  `systemd/units` reactor in `~/Projekte/ckn-bw/bundles/left4me/metadata.py`
+  (the hardening refactor we just landed reinforced this).
+- sysctl options ended up in ckn-bw `bundles/left4me/metadata.py`
+  `defaults` (just landed too).
+- sudoers exists in *both* repos (left4me `deploy/files/.../sudoers.d/left4me`
+  + ckn-bw verbatim mirror).
+- Privileged helpers moved BACK to left4me as part of deploy-dir-rethink
+  (commit `5284e28`) — `scripts/{libexec,sbin}/`. Pattern works:
+  left4me defines, ckn-bw deploys via `install_left4me_scripts`.
+
+So the trajectory has been mixed: helpers re-converged on left4me
+(good, matches 2026-05-06); systemd units + sysctl drifted into
+ckn-bw (away from 2026-05-06). The brainstorm reconciles this.
+
+**The question**: should we return to the 2026-05-06 model
+end-to-end — every deployment artifact lives in left4me's
+`deploy/files/`, ckn-bw becomes a thin integrator — or is the
+current mixed shape the right answer for some artifact classes?
+
+## Operator's leaning
+
+Security-related artifacts belong **in the left4me repo**, owned by
+the project; ckn-bw is responsible for **integrating** them into the
+host (deploying them to the right paths, restarting affected units,
+etc.) but doesn't *author* them.
+
+Concretely the operator's preference (from session
+2026-05-15): "security-related stuff should be bundled in this repo
+and ckn-bw is responsible for integrating it into the server."
+
+## Why we're doing this
+
+Background from the hardening-refactor session
+(`docs/superpowers/specs/2026-05-15-hardening-refactor-design.md`,
+"Approach" section). We considered two shapes for the hardening
+landing:
+
+- **A** — hardening directives inline in ckn-bw's `systemd/units`
+  reactor (the path we took)
+- **B** — hardening as drop-in `.conf` files living in left4me's
+  `deploy/files/etc/systemd/system/<unit>.d/`, ckn-bw deploys them
+  (consistent with 2026-05-06's `deploy/files/` model)
+
+We picked A for the hardening refactor because B implied a broader
+configmgmt responsibility reshape that deserved its own session.
+That session is this one.
+
+The motivating arguments for B (this brainstorming session evaluates
+them seriously):
+
+1. **Hardening is application knowledge.** Knowing srcds is i386,
+   that `MemoryDenyWriteExecute=true` breaks Source's text
+   relocations, that web's sudo path is incompatible with
+   `PrivateUsers=true` — all of this is left4me's domain, not
+   ckn-bw's. ckn-bw shouldn't need to understand the threat model.
+2. **Test-artifact = production-artifact.** The Test 7 drop-in from
+   the hardening test plan literally is the file we'd want
+   deployed. With B, there's no translation step.
+3. **Repo self-containment for security review.** A reviewer of
+   left4me sees the threat model in code form without needing to
+   read the configmgmt repo.
+4. **Easier coordination with the `build-overlay-unit` refactor**
+   (queued). That unit's hardening profile can ship in its own
+   drop-in inline with the unit template.
+
+The counter-argument:
+
+- **Coupling cost.** A change to a directive may require redeploying
+  via ckn-bw, which means a cross-repo coordination cycle (edit
+  left4me → commit → push → ckn-bw `bw apply`). Today the same is
+  true (edit ckn-bw → push → apply); just the *which* repo changes.
+
+## What "security-related" likely means
+
+Enumerate during the brainstorm. Initial candidates:
+
+- **systemd unit hardening directives** — currently in
+  ckn-bw `bundles/left4me/metadata.py` `HARDENING_COMMON` /
+  `HARDENING_SERVER` / `HARDENING_WEB`. Strong candidate for left4me.
+- **sysctl drop-ins** — currently `kernel.yama.ptrace_scope=2` in
+  ckn-bw's left4me bundle `defaults` (`sysctl/kernel/yama/ptrace_scope`).
+  Strong candidate for left4me.
+- **sudoers** — already in `left4me/deploy/files/etc/sudoers.d/left4me`
+  + a verbatim mirror in `ckn-bw/bundles/left4me/files/etc/sudoers.d/left4me`.
+  Already mostly left4me-owned; redundancy worth resolving.
+- **Privileged helper scripts** — already in `left4me/scripts/{libexec,sbin}/`,
+  ckn-bw deploys them via `install_left4me_scripts`. Already
+  left4me-owned. The pattern works.
+- **systemd unit BASE definitions** (`User=`, `ExecStart=`, `Restart=`,
+  resource limits) — currently in ckn-bw's reactor. **Open question:**
+  is this application knowledge or infrastructure knowledge? They
+  depend on the application's binary paths, env files, restart
+  semantics — all application knowledge. Probably also belongs to
+  left4me.
+- **AppArmor profiles** (if we add them later — deferred from the
+  defenses survey). Application knowledge.
+- **`/etc/left4me/host.env` / `web.env` templating** — ckn-bw owns
+  these today because they're templated via mako from node metadata
+  (per-host overrides). Probably stays in ckn-bw.
+- **User/group creation** — kernel-side infrastructure, no
+  application knowledge needed. Stays in ckn-bw.
+- **Package installation** (apt). Stays in ckn-bw.
+- **Firewall rules** — depend on per-instance port ranges
+  (`LEFT4ME_PORT_RANGE_*`); could be either. Worth discussing.
+- **Nginx vhost** — same: depends on app-specific routes.
+
+## Mechanism: how does ckn-bw "integrate"?
+
+Brainstorm the deploy mechanism. Candidates (already partially
+sketched in the hardening-refactor design doc's earlier draft, before
+it was reverted to the inline-in-reactor approach):
+
+- **Symlinks.** ckn-bw creates symlinks like
+  `/etc/systemd/system/left4me-server@.service.d/10-hardening.conf`
+  → `/opt/left4me/src/deploy/files/etc/systemd/system/.../10-hardening.conf`.
+  Editing the file in the repo + `systemctl daemon-reload` picks it
+  up. Cleanest for "ckn-bw doesn't author."
+- **File copy via `files` entries.** ckn-bw `files = {...}` reads
+  from `/opt/left4me/src/deploy/files/...` (post-git_deploy) and
+  copies to the target. Standard idiom. Two-place state.
+- **Glob-walker action.** A small ckn-bw action walks `deploy/files/`
+  tree and mirrors paths to root.
+- **Bundle inclusion / left4me-as-bundle.** Left4me's `deploy/`
+  becomes its own bundlewrap bundle that ckn-bw imports. Strongest
+  decoupling; requires bundlewrap bundle conventions.
+
+Each has different implications for: triggers (which units restart
+when which files change), drift detection, rollback semantics.
+
+## Migration / coexistence path
+
+Brainstorm: how do we get from the current state to the new state
+without breaking things?
+
+- Inventory: every artifact ckn-bw currently emits/ships for left4me
+  (the `systemd/units` reactor entries, sysctl defaults, sudoers
+  mirror, file deploy actions, etc.).
+- For each: stays, moves, or split (some in each).
+- Mechanism rollout: pick one (symlinks vs. file copy vs. ...) and
+  apply it consistently.
+- Test-driven: pick one artifact as the canary (probably the sysctl
+  drop-in — smallest), validate the mechanism end-to-end, then
+  migrate the others.
+
+## Key sub-questions for the brainstorm
+
+1. **Is the unit's BASE definition application knowledge?** If yes,
+   ckn-bw's `systemd/units` reactor shrinks dramatically — to maybe
+   one line per unit ("ckn-bw, deploy this file as a unit"). If no,
+   we have a more delicate split.
+2. **What about the user/group definitions?** Infrastructure-side
+   today. But the application defines that `left4me` (uid 980)
+   exists; ckn-bw just creates it. Could move.
+3. **Per-host configuration** (gunicorn worker count, port ranges,
+   CPU pinning): these are per-host overrides ckn-bw computes from
+   node metadata. Stays in ckn-bw (or whatever owns deployment-time
+   parameterization).
+4. **Test infrastructure**: `deploy/tests/test_deploy_artifacts.py`
+   asserts left4me's reference units match the deployed form. If
+   left4me starts owning the deployed form, those tests get
+   stronger (no longer "reference vs. live" drift; the file in
+   `deploy/files/` *is* the live form).
+5. **Drift / observability**: how do we know the deployed state
+   matches the repo? Today `bw apply` + git diff is the source of
+   truth. Same applies; mechanism details vary.
+6. **Rollback semantics**: removing a drop-in is one `rm` away; the
+   base unit is preserved. Same applies to reverting the
+   left4me-side commit and re-applying.
+
+## Prereqs (must land before this brainstorming session)
+
+- **uid-collapse refactor** — queued in
+  `docs/superpowers/plans/2026-05-15-uid-collapse.md`. Settles the
+  user model first so the deployment-responsibility brainstorm
+  doesn't have to juggle a moving user definition.
+
+## Out of scope for the brainstorm
+
+- The hardening composition itself (already settled, deployed,
+  verified).
+- The `build-overlay-unit` template unit refactor
+  (`docs/superpowers/specs/2026-05-15-build-overlay-unit-design.md`)
+  — both this brainstorm *and* the build-overlay-unit refactor
+  benefit from settling responsibility first. Sequencing TBD; the
+  brainstorm should consider whether to land before or after
+  build-overlay-unit.
+- The application code itself (`l4d2web`, `l4d2host`) — that's
+  always been left4me-owned.
+
+## Pointers
+
+- **Original deployment design (the model to revisit):**
+  `docs/superpowers/specs/2026-05-06-left4me-deployment-design.md`
+- Hardening refactor design (motivation; the deferred reshape):
+  `docs/superpowers/specs/2026-05-15-hardening-refactor-design.md`
+- Hardening refactor plan (what got landed):
+  `docs/superpowers/plans/2026-05-15-hardening-refactor.md`
+- Defenses survey (mentions AppArmor, deferred):
+  `docs/superpowers/specs/2026-05-15-hardening-defenses-survey.md`
+- Test plan + executed results:
+  `docs/superpowers/specs/2026-05-15-hardening-test-plan.md`
+- uid-collapse plan (prereq):
+  `docs/superpowers/plans/2026-05-15-uid-collapse.md`
+- deploy-dir-rethink (recent reshape that moved scripts into left4me;
+  background on the current `deploy/` tree):
+  `docs/superpowers/plans/2026-05-15-deploy-dir-rethink.md` (or
+  `2026-05-15-deploy-dir-rethink-design.md`)
+- Live ckn-bw bundle (the thing being rethought):
+  `~/Projekte/ckn-bw/bundles/left4me/`
diff --git a/docs/superpowers/specs/2026-05-15-session-handoff.md b/docs/superpowers/specs/2026-05-15-session-handoff.md
index a891fa0..bec647a 100644
--- a/docs/superpowers/specs/2026-05-15-session-handoff.md
+++ b/docs/superpowers/specs/2026-05-15-session-handoff.md
@@ -100,7 +100,9 @@ Operator picked C.
   (`docs/superpowers/specs/2026-05-15-build-overlay-unit-design.md`).
   Sequenced after this; will inherit `User=left4me` cleanly.
 - **Broader configmgmt responsibility reshape** (drop-ins owned by
-  left4me, ckn-bw as thin file-shipper). Deliberately deferred.
+  left4me, ckn-bw as thin file-shipper). Framed as a brainstorming
+  session at `docs/superpowers/specs/2026-05-15-handoff-deployment-responsibility.md`;
+  sequenced after uid-collapse lands.
 - **Stale RCON port app bug** flagged in the earlier executor's
   handoff. Separate scope.
 - Renaming `left4me` to anything else. Cosmetic.