refactor: split oversized production files to satisfy repository policy

[ninthworld]

Parent: #713.

Updated 2026-08-07 against main at 47e26cc. Every file the original body named has since
been split. The policy breach did not go away with them — the M19 tranche (#706) regrew the same
seams under new names, so the file list below is current and the old one is preserved at the
bottom as the before-half of the record this issue's acceptance criteria ask for.

Problem

Root AGENTS.md sets an approximately 800–1,000-line limit and docs/coding-standards.md calls
1000+ a hard smell to break up before adding more code. Twelve production source files exceed
1,000 lines, counting code only — a file's own #[cfg(test)] mod tests { … } block is excluded,
and files whose tests live in a sibling tests.rs are counted in full.

File	Code lines
crates/sage-engine/src/ability/effect.rs	1,936
crates/sage-server/src/rules_text/effects.rs	1,625
crates/sage-engine/src/state/zone.rs	1,236
crates/sage-engine/src/apply/cast/targeted.rs	1,232
crates/sage-engine/src/triggers.rs	1,225 (of 1,631 total)
crates/sage-engine/src/apply/cast/effects.rs	1,195
crates/sage-engine/src/choice/mod.rs	1,163
crates/sage-server/src/rules_text.rs	1,152
crates/sage-engine/src/state/types.rs	1,119
clients/web/src/interaction.ts	1,108
crates/sage-engine/src/resolve.rs	1,039
clients/web/src/protocol.ts	1,002

Six more sit in the 800–1,000 soft-ceiling band and are worth watching rather than splitting now:
clients/prototype/src/App.tsx (963), crates/sage-engine/src/actions/generation.rs (863),
crates/sage-engine/src/catalog/effects.rs (858), clients/web/src/ui/game/Board.tsx (857),
crates/sage-protocol/src/card.rs (831), crates/sage-engine/src/actions/definition.rs (801).

clients/prototype/src/styles.css (3,228) is out of scope: the prototype is a throwaway
sandbox and the repository's design and structure doctrine does not govern it.

These are again exactly the seams the next rules or protocol work will land in — ability/effect.rs
and rules_text/effects.rs are the two halves of the same vocabulary, and every card added widens
both.

Scope

Perform behavior-preserving splits along cohesive existing domains with root re-exports. Sequence
the work in small PRs rather than one repository-wide rewrite.

Suggested waves, in payoff order:

1. The effect vocabulary — ability/effect.rs and its rules-text mirror
   sage-server/src/rules_text/effects.rs, split along the same domain seams so the two stay
   readable against each other.
2. Engine state — state/zone.rs and state/types.rs.
3. Cast application — apply/cast/targeted.rs and apply/cast/effects.rs, which were
   themselves produced by the previous wave and have since regrown.
4. Triggers, choices, and resolution — triggers.rs, choice/mod.rs, resolve.rs.
5. Client — interaction.ts and protocol.ts.

Acceptance criteria

• No production source file remains materially above the documented limit without a written exception.
• Public APIs and serialized wire shapes remain unchanged.
• Each split is single-purpose and reviewable.
• Existing unit, integration, parity, agent-game, and browser tests remain green.
• Module boundaries follow domain ownership rather than arbitrary line-count chunks.
• No mechanic or product behavior is added in the refactor PRs.
• Before/after line counts are recorded.

Non-goals

• Broad renaming or formatting churn.
• New abstractions without an existing domain seam.
• Combining rules expansion with structural refactoring.

---

Original list (2026-08-04) — all of these are now split

Sixteen non-test production files exceeded 1,000 lines; the largest and most central were:

• crates/sage-engine/src/apply/cast.rs — ~2,696
• crates/sage-engine/src/apply/combat.rs — ~2,104
• crates/sage-engine/src/ability.rs — ~1,849
• crates/sage-server/src/lobby/commands.rs — ~1,521
• crates/sage-engine/src/characteristics.rs — ~1,398
• crates/sage-server/src/lobby.rs — ~1,332
• crates/sage-server/src/view/requirements.rs — ~1,262
• crates/sage-protocol/src/lobby.rs — ~1,215
• crates/sage-server/src/rules_text.rs — ~1,190
• seven additional production files between ~1,017 and ~1,168 lines

Not one of them is over the limit today: cast.rs became apply/cast/, combat.rs became
apply/combat/, ability.rs became ability/, characteristics.rs became characteristics/
with a module per CR 613 layer, and the server's lobby, view, and protocol files split the same
way. rules_text.rs is the one that came back — it is 1,152 lines again, with a
rules_text/effects.rs of 1,625 beside it.