Add The Frontier, a second setting, and a picker to choose between them

Cold Fork is a freight yard: 29 events across two stages, a four-day cycle, and
its own relationship and skill vocabulary. src/engine/ was not touched. Adding it
needed three changes outside the engine: one save slot per pack, app.js holding
the current pack, and turn.js no longer naming the mailroom (DECISIONS #34).
build.js now handles imports wrapped across lines. A conformance suite runs over
every registered pack. DECISIONS #35 records three calls on open questions.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RxdJFbLq1rBKsUeticGV1g

docs/DECISIONS.md

@@ -421,3 +421,129 @@ Spans and pair-counts are now accumulated per run and pooled, so the figure is a
 proper weighted average of within-run gaps. It is worth stating the general
 form: any statistic over a log has to respect the run boundary, because a log is
 not one sequence.
+
+## 31. A pack declares the numbers it must hit
+
+Decision #29 added a test that asserts Corporate Ladder's economic baseline
+directly, because a tuning change made without re-deriving what it meant had
+trapped a real playtester. That test named the pack, named its stages and
+hard-coded its ranges, which meant a second pack got none of it — the guard
+that exists precisely because a number went unchecked would itself have gone
+uncopied.
+
+So the numbers moved into the pack, as `tuning.baselinePerCycle`:
+
+```js
+tuning: {
+  baselinePerCycle: { hand: [0, 12], deputy: [10, 30] },
+},
+```
+
+The conformance suite reads that and holds each pack to its own declared range.
+A new setting is checked the moment it is in the registry, and what it is
+checked against is its designer's stated intent rather than another setting's
+numbers. The pack is required to declare it: a missing `tuning` block fails,
+because the silent failure mode here is a pack that is never economically
+tested at all.
+
+The figure is **derived, not simulated**. An upkeep entry worth `v` every `n`
+turns is worth `v * cycleLength / n` per cycle, exactly. Simulating it over a
+fixed window reads differently depending on where the last rent lands: Corporate
+Ladder measures −19 a fortnight over 280 turns and −42 over 560, and only the
+second is the steady state. The original test used the 280-turn window and was
+reading a number 23 dollars off the truth — inside its own tolerance, so it
+never said so.
+
+## 32. A skill gate is never gated behind itself
+
+Corporate Ladder gates four options on `skills.negotiation >= 15`, and several
+of its largest negotiation gains sit behind that same gate — `+4` on
+`marlene_confides.ask_how_to_leave`, `+3` on `trevor_favor.trade`. Its logs show
+players meeting the wall repeatedly through the first thirty turns.
+
+Measured, the gate is not unreachable: a player steering directly for the skill
+is through it by turn 11. What the logs actually show is ordinary players not
+prioritising it and having no incidental route, which is a pacing failure rather
+than a reachability one — and the reachability test could never have caught it,
+because reachability is exactly what holds.
+
+The Frontier is built to a rule instead, asserted in `test/frontier.test.js`:
+for every skill threshold in the pack, the growth available *without* passing
+that threshold must be able to reach it, from repeatable events — a single
+one-off award is not a route. A second test measures it, requiring a player who
+steers for a skill to be through its lowest gate inside twenty turns.
+
+The rule is deliberately not in the conformance suite, because Corporate Ladder
+does not satisfy it and retuning that pack is a separate decision from adding
+this one. It is written down here so the choice is visible rather than implied.
+
+## 33. One save slot per pack, and the picker is the front door
+
+`theladder.save.v1` was a single global slot. The app guarded it by comparing
+the packId inside the save against the pack it was about to run, and started a
+new game when they differed — so with two settings, the first switch would have
+silently destroyed the other career.
+
+Slots are now `theladder.save.v1.<packId>`, one per setting, and switching is
+non-destructive in both directions: each run is written to its own slot every
+turn, and coming back resumes rather than restarts. `theladder.pack.v1` holds
+the last setting played, so a returning player lands back where they were.
+
+The pre-packs slot is still read once, for Corporate Ladder only, and only when
+it really holds a Corporate Ladder save. It is never written. Someone mid-career
+when this shipped finds their career.
+
+A first-time player — nothing saved, nothing remembered — gets the setting
+picker rather than being dropped into whichever pack is first in the registry.
+A build shipping one pack skips it entirely.
+
+## 34. What a second setting proved, and what it cost
+
+The engine/content split was a claim until there were two settings. The
+Frontier is 29 events across two stages, a four-day cycle instead of a
+seven-day one, a different relationship vocabulary (`trusts_you`, `owes_you`,
+`wary_of_you`), a different skill pair, and money about fifteen times smaller
+that arrives from work rather than from a wage. `src/engine/` was not touched.
+
+Three things outside the engine did have to change, and none of them was about
+the setting:
+
+- **`src/io/save.js`** — the single save slot, above.
+- **`src/ui/app.js`** — it named one pack; it now holds the current one. The
+  screens, the engine and the rest of the io layer still take the pack as an
+  argument and are no less pack-agnostic than before.
+- **`src/ui/screens/turn.js:40`** — hardcoded `'The mailroom'` as the heading
+  over the people panel. That was the interface naming a setting, against
+  decision #14, and it had gone unnoticed while only one setting existed. It is
+  now `pack.peopleHeading`.
+
+`tools/build.js` needed one fix, unrelated to packs but exposed by them: its
+module scan used `.*?` where `transform` used a pattern that spans lines, so a
+destructured import wrapped across several lines was rewritten into a
+`__require` for a module the scan had never collected. The bundle built clean
+and failed only when run. Both now use `[\s\S]*?`.
+
+The honest summary is that adding a setting required no engine change and three
+interface changes, two of which were latent defects that a second pack merely
+made visible.
+
+## 35. Three open questions, closed by the designer
+
+Recorded 2026-09-11, alongside 0.3.1.
+
+**Corporate Ladder's negotiation gate stays.** A gate that takes deliberate work
+to get past is acceptable, and so is an option that needs groundwork first. #32
+remains the rule the Frontier is built to and tested against; it is a choice a
+pack may make, not a standard every pack must meet, and Corporate Ladder is not
+being retuned toward it.
+
+**The feedback widget stays exactly as it is.** Zero ratings across three
+sessions says nothing about the widget: those playtests were rapid, and feedback
+came back directly rather than through it. It is not evidence either way until a
+playtest runs without that direct channel.
+
+**Money has to matter late, through the cost of standing.** A careful player
+ends around $8,300 over 200 turns, and money stops being a constraint. The
+direction is that rising standing brings rising expenses — the car, the place to
+live, the clothes a position expects. Upkeep entries are already gated
+conditions over state, so this is content work, not an engine change.