Document docker-compose.<host>.yml fallback for list-replacement deltas

docs/strategy.md

@@ -46,38 +46,64 @@ Some stacks run on **multiple hosts** with the same image but slightly different
 
 ```
 Charlie/<stack>/
-├── docker-compose.yml             # the "what" — same on every host
+├── docker-compose.yml             # the "what" — default, used by hosts without an override
+├── docker-compose.<host>.yml      # full per-host compose (when the delta is structural)
 ├── envs/
 │   ├── morgott.env                # per-host env (Ansible host_vars equivalent)
 │   ├── melina.env
 │   ├── mohg.env
 │   └── miquella.env
-├── overrides/                     # only when env can't express it (volumes, services)
-│   └── miquella.yml               # Kustomize overlay equivalent — usually absent
-├── deploy.sh                      # picks env + override based on `hostname -s`
+├── overrides/                     # additive overlay deltas (when env can't express it)
+│   └── <host>.yml
+├── deploy.sh                      # picks env + compose file based on `hostname -s`
 └── README.md
 ```
 
-### Rules
+### Resolution order in `deploy.sh` (per host)
 
-- `docker-compose.yml` is **canonical** and works on every host as long as the right env file is loaded. Use `${VAR:-default}` liberally.
-- `envs/<host>.env` is tracked in git (no secrets). Secrets-bearing values come from a separate gitignored `.env` (host-local) merged in at deploy time, OR from runtime secret sourcing (vaultwarden, deferred).
-- `overrides/<host>.yml` only exists when env vars genuinely can't bridge the difference (e.g. extra volume bind, service add/remove, network change). Aim for zero override files; one or two is acceptable.
-- `deploy.sh` is the host-side entrypoint. Always:
-  ```bash
-  HOST=$(hostname -s)
-  args=(--env-file "envs/$HOST.env" -f docker-compose.yml)
+1. If `docker-compose.<host>.yml` exists → use **only** that (full per-host compose).
+2. Else `docker-compose.yml` + (if present) `overrides/<host>.yml` layered on top.
+3. If `envs/<host>.env` exists → loaded with `--env-file` in either case.
+
+Hostname is lowercased (`hostname -s | tr '[:upper:]' '[:lower:]'`).
+
+### When to use which
+
+| Delta type | Use |
+|---|---|
+| Different scalar value (port, env var, URL) | `envs/<host>.env` |
+| Add an extra service or scalar field | `overrides/<host>.yml` (compose merges additively) |
+| **Replace** a list (volumes, command, networks) | `docker-compose.<host>.yml` (full file) |
+| Different image | `docker-compose.<host>.yml` |
+
+Compose's `!override` and `!reset` YAML tags exist for list-replacement, but support is uneven across compose versions (notably broken on Synology DSM's bundled compose). Prefer the full-file approach when replacing lists.
+
+### Canonical `deploy.sh`
+
+```bash
+#!/usr/bin/env bash
+set -euo pipefail
+cd "$(dirname "$0")"
+HOST=$(hostname -s | tr '[:upper:]' '[:lower:]')
+
+if [ -f "docker-compose.$HOST.yml" ]; then
+  args=(-f "docker-compose.$HOST.yml")
+else
+  args=(-f docker-compose.yml)
   [ -f "overrides/$HOST.yml" ] && args+=(-f "overrides/$HOST.yml")
-  sudo docker compose "${args[@]}" "$@"   # forward `up -d` / `pull` / `down` / etc.
-  ```
+fi
+[ -f "envs/$HOST.env" ] && args=(--env-file "envs/$HOST.env" "${args[@]}")
+
+exec sudo docker compose "${args[@]}" "$@"
+```
 
 ### Mental model
 
-- "What" = `docker-compose.yml`
-- "Where" = the host running `./deploy.sh` (no inventory file needed; the host knows its own name)
-- Per-host vars = `envs/<host>.env` (Ansible `host_vars`)
-- Per-host structural deltas = `overrides/<host>.yml` (Kustomize overlay)
-- Group defaults = compose env-var defaults (`${VAR:-default}`)
+- "What" = `docker-compose.yml` (or per-host file).
+- "Where" = the host running `./deploy.sh` (no inventory file; the host knows its own name).
+- Per-host vars = `envs/<host>.env`.
+- Per-host structural deltas = `overrides/<host>.yml` for additive, `docker-compose.<host>.yml` for replacement.
+- Group defaults = compose env-var defaults (`${VAR:-default}`).
 
 ### Once runners exist (Phase 2)