chore: document optional FFXI-style sub-gig slot

docs/game-design/skills.md

@@ -10,6 +10,7 @@ From here on in game-design docs:
 |------|--------|
 | **Gig** | The **combat role** (combat “class”): what you bring to a fight—kit, tuning band, party expectations. Not used for crafting or gathering. |
 | **Skill** | A **non-combat** trained capability only (gather, craft, etc.). Never used to mean the combat gig. |
+| **Sub-gig** | *(If we ship it.)* A **secondary gig** paired with your **main gig** on one loadout. Used for **limited** cross-gig ability access—see [Sub-gigs](#sub-gigs-optional-ffxi-style) below—not for crafting or replacing the main gig’s identity in combat. |
 
 Fiction and UI may still say *job*, *contract*, or *loadout* in dialogue; design vocabulary stays **gig** / **skill** to avoid ambiguity.
 
@@ -26,6 +27,14 @@ A **gig** is the **combat identity** you bring to a fight: ability access, basel
 - **Progression per gig:** separate level/track vs. shared “combat rank” with gig-specific unlocks—**open**; separate tracks support “I main tank but leveled medic for backup” at the cost of more balancing.
 - **Mastery/perks** can attach to **gigs** (combat expression) while **skills** use the same *idea* for craft depth (E2.M3-style), or stay separate—**open**.
 
+### Sub-gigs (optional, FFXI-style)
+
+We may add a **sub-gig** slot so one loadout mixes two gigs without full dual-main power.
+
+- **Reference pattern (FFXI-style):** at **main gig** level **X**, the **sub-gig** contributes abilities (and any sub-gated systems) only as if that gig were **⌊X / 2⌋**—exact floor/rounding and whether “level” means character combat rank vs. per-gig progress is **TBD**.
+- **Intent:** hybrid builds and party coverage (e.g. main damage + sub support tools) without letting a sub match a fully leveled second gig.
+- **Still open:** sub-gig **swap** rules, **gear** (likely still **main-gig–restricted** for combat gear; sub only feeds **abilities**), **consumable** amplification (main vs. sub), **PvP** ceilings, and UI (two gig strips on HUD).
+
 ## Skills (non-combat, classless)
 
 Everything **outside combat role resolution**—gathering, refining, crafting lines, non-combat tech, etc.—uses **skills**:
@@ -83,11 +92,12 @@ Categories group skills for **UI and balance** (e.g. *Gathering*, *Craft*, *Tech
 | Failure XP | Per-activity; watch exploits | Open |
 | Skill caps | Prefer soft; hard only if economy/PvP needs | Proposed |
 | Gig swap rules | — | Open |
+| Sub-gig | Optional **FFXI-style** slot: sub abilities up to **~½ main gig level** (formula TBD) | Open |
 | Shared vs. per-gig combat progression | — | Open |
 | Epic 2 doc split | Align modules when gig data model is chosen | TBD |
 
 ## Next artifacts
 
-- **Gigs** — roster size, swap UX, party finder tags, PvP ([overview](overview.md)).
+- **Gigs** — roster size, main vs. **sub-gig** UX, swap rules, party finder tags, PvP ([overview](overview.md)).
 - **Abilities** — **gig-locked** vs. **item-locked** vs. **skill-gated**.
 - **Items** — **equip:** gig rules; **craft:** **skills** (and recipe/rep), never gig level.