Add chance and a cast that changes between runs, and a pack to try them

An option used to do exactly what it said. Now it may carry a check: one of
four attributes (Nerve, Wits, Charm, Resolve) against a set difficulty or
against a named person's own attribute, leaning on how they regard you, with a
success and a failure. The player sees only the odds in words ("a long shot",
"likely"), never a number. The roll is one draw from the run's generator, so a
run still replays exactly from its seed and choices.

A character may be a role with several authored candidates, one drawn per run,
or a group of two to four drawn into numbered slots. Everyone carries a name, a
description and the same four attributes as the player, so a replayed pack
meets a different office. Text names people as {partner} or {clerk}, and an
event about "a clerk" binds one present clerk for the turn. The draw and the
binding are saved with the run, and a save from before a pack drew a cast gets
the same one every time it is loaded.

All of it is generic and optional: Corporate Ladder and the Frontier use none
of it and play as before. The Counting House, a one-stage office about 1910
built from the story-to-pack catalogue, exercises it, and was tuned against the
conformance suite by measurement. DECISIONS #41. Version 0.4.0.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018MhABSrqkwTdcybXmheDPr

docs/DECISIONS.md

@@ -765,3 +765,92 @@ whether money stops mattering again, as it did in Corporate Ladder before #36.
 "Owed at the store" was asked for as "a major field at the top". It already is,
 second after Money whenever anything is owed. Whether it is prominent enough can
 only be judged in a browser, which this machine cannot render (#18).
+
+## 41. Chance, and a cast that changes between runs
+
+Recorded 2026-09-23. Designer's call: a change to the base engine, generic, which
+every pack may use and none has to. Corporate Ladder and the Frontier use none of
+it and replay exactly as before.
+
+Until now an option did exactly what it said. Skills only decided whether an
+option was on the menu (#15, #32). The story-to-pack catalogue of recurring
+situations (asking for a rise, the door to the powerful, a colleague's needling)
+is made of moments whose outcome depends on who you are and who you are dealing
+with, so three things were added. `content/countinghouse` is the pack that exercises them.
+
+**Attributes.** A pack names them in `pack.attributes`. The player's live in
+ordinary declared state (`attributes.<id>`), so they grow by effects like anything
+else. The prototype's four, agreed with the designer, are Nerve, Wits, Charm and
+Resolve. Another pack may rename them, as #14 lets it rename the interface.
+
+**Checks.** An option may carry `check: { attribute, against?, opposedBy?,
+relationship?, difficulty?, modifier? }` and then must carry `success` and
+`failure`, each with its own `result` and `effects`. Its plain `effects` apply
+either way. The chance is
+
+    base + perPoint × (yours − theirs) + relationshipPerPoint × (their regard − centre) + modifier,
+    clamped to [floor, ceiling]
+
+where "theirs" is the opposing character's attribute, or the check's `difficulty`,
+or the pack's `unopposed`. Every number is the pack's, in `pack.checks` (#9).
+**The player never sees a number.** Options show the odds in words ("a long shot",
+"likely"), from bands the pack may rename, and the outcome says whether it came
+off. The roll is one draw from the run's own generator, so a run with checks still
+replays exactly from its seed and choices (#5, #6). A pack that never checks draws
+nothing extra.
+
+**A cast drawn per run.** A character may be a *role* with `candidates`, several
+authored people who could fill it, and one is drawn when a run starts. A role may
+be a *group* with `count: [min, max]` (two to four clerks), which draws that many
+different people into numbered slots (`clerk_1` .. `clerk_4`). Every candidate
+carries a name, a description and the same attributes the player has, so a
+replayed pack meets a different office with different strengths. Candidates are
+authored rather than generated from random parts: a character written as sharp
+has the wits to see through a bluff, which a random attribute roll pasted onto a
+random description would not guarantee.
+
+- **The draw is saved in engine-owned state** (`cast`, now a reserved root, #4)
+  and made on its own stream derived from the seed, so it neither moves the event
+  generator nor depends on it. `hydrate` (#36) draws one for a save that predates
+  it, and draws the same one every time.
+- **Every slot up to a group's maximum is declared in the schema from the start.**
+  Relationship state for `clerk_3` exists whether or not anyone was drawn into it,
+  so it validates and saves like any other path. An empty slot is recorded as
+  `null` and is simply absent from the run.
+- **Text names people by role.** `{partner}`, `{chief.first}` and `{clerk.title}`
+  are filled in from whoever was drawn. An event about "a clerk" says
+  `involves: ['clerk']`. When it is drawn, one present clerk is bound to it for
+  the turn, and `{clerk}` in its text, `relationships.{clerk}.trust` in its effects
+  and `against: '{clerk}'` in a check all mean that person. The binding is saved
+  with the run. An event cannot fire in a run with nobody to bind. Text kept in
+  state, such as a notable moment, has its placeholders pinned to the slot
+  (`{clerk_2}`), so the retrospective names the right person later.
+- **The validator holds all of it:**
+  - attributes declared, and every drawn person carrying all of them;
+  - enough candidates for a group's maximum, and unique names;
+  - checks naming real attributes and people, with both branches;
+  - `{placeholders}` that name real characters, where a group is only named inside an event that binds it;
+  - no placeholder in an event's own `requires`, which is evaluated before anyone is bound.
+
+**What the test harness had to learn.** The archetypes score an option by its
+effects (#21). A checked option is now scored at its expected value: plain effects
+in full, and each branch weighted by its chance, the way a player reading the odds
+would. The conformance check that no repayment takes more than is owed (#38) now
+reads both branches, since a check can pay or spend on either.
+
+**The prototype pack was tuned by measurement, not by eye.** Its first draft
+failed three conformance tests:
+- the routine ledgers were a third of every player's turns;
+- a careless player was broke 40% of a run;
+- it had no balance a borrower could owe.
+
+Two more catalogue situations (an errand for the partner's family, and a desk you
+and a clerk both want), a lighter floor event, a loan that is refused but still
+helps a little, and an "owed to the floor" balance repaid on Saturdays brought
+those to 22% at worst, 12% at worst, and a debt that is repaid by reading the
+balance (#38).
+
+**Not yet known.** Whether chance makes the same situations worth replaying, and
+whether the odds in words are legible, can only be judged by someone playing it
+(#18). The pack has one stage on purpose, so that question can be answered before
+a career is built on it.