spec(hardening-refactor): resolve emitter open items

Verified during plan execution that the ckn-bw systemd-bundle emitter
handles tuples and empty values as expected. SocketBindAllow port
range hard-coded since systemd directive variable substitution is not
universal.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/superpowers/specs/2026-05-15-hardening-refactor-design.md

@@ -202,13 +202,25 @@ reference unit points readers at the reactor.
   scope.
 - **Pushing the branch** — operator decides when.
 
-## Open items resolved in implementation, not design
+## Implementation notes (resolved during plan execution)
 
-- Does the systemd-bundle emitter handle `('a', 'b')` tuples as
-  repeated `Key=` lines, and `''` as `Key=` empty value? Verify as the
-  first step of the plan; fallback strategies if not.
-- `SocketBindAllow=` value: hard-coded range vs. variable
-  substitution. Determined during emitter verification.
+- The ckn-bw systemd-bundle emitter renders Python tuples as repeated
+  `Key=Value` lines and renders empty strings as `Key=` with no value.
+  Both behaviors confirmed by reading the Mako template in
+  `libs/systemd.py:17-23`. Tuple branch: `isinstance(value,
+  (list, set, tuple))` iterates and emits `${option}=${item}` per
+  element, preserving insertion order (sets are sorted; lists and
+  tuples are not). Empty-string branch: falls through to `else:
+  ${option}=${str(value)}`, which emits `Key=` with nothing after `=`.
+  `None` suppresses the key entirely (distinct from empty string —
+  important). The `protection()` helper at `libs/systemd.py:94` already
+  uses `'CapabilityBoundingSet': ''` as a live in-repo example. Tuple
+  precedent in the left4me bundle: `EnvironmentFile` at
+  `bundles/left4me/metadata.py:201-204`. Verified 2026-05-15.
+- `SocketBindAllow=` value: hard-coded port range `27000-27999` for
+  both `udp:` and `tcp:` lines (matches the `LEFT4ME_PORT_RANGE_*`
+  metadata values). Variable substitution in systemd directives is not
+  universally supported; hard-coded range avoids the hazard.
 
 ## Pointers