Keep every retried attempt instead of deleting it

Retry used to delete the last AI action and generate a replacement, so the
discarded narration was simply gone. The row survives now: each attempt is
appended to actions.variants with variant_index naming the live one, and a
ChatGPT-style pager under the message browses them.

Action.text still mirrors the active variant, so the context builder, memory
bank, summarizer and export needed no changes. A variant carries only what
differs between attempts -- the text, the reasoning, and the state it
produced -- never the assembled prompt, which is identical across attempts of
one turn and is the bulk of context_snapshot.

Only the last message can be switched, restoring the script/world state that
attempt produced; earlier turns were written as a continuation of whatever is
active there, so theirs are read-only previews.

Three things that would otherwise bite:

- generate_turn now wraps _generate_turn and watches for a save sentinel. If
  the generator ends without it (provider error, empty reply, script stop,
  client hangup) it re-applies the previous variant -- otherwise a failed
  retry leaves rolled-back stats under un-rolled-back text.
- Retry reuses the turn's own index rather than next_index, or the clock the
  world-state cooldowns run on advances on a re-run of the same turn.
- Editing a message rewrites the active variant too, or paging away and back
  silently reverts the edit.

Migrations 34/35 verified as an upgrade against a populated database, not
just a fresh schema. test_state_revert's retry test asserted the old delete
behaviour and was rewritten.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UeQVy5bEjLhfgWNc27Efet

backend/app/schemas.py

@@ -183,9 +183,26 @@ class ActionOut(ORMModel):
     reasoning: str | None = None
     # Phase 12: compact RPG state changes for this turn (from the model property).
     world_changes: list[dict] = []
+    # Retry history: how many attempts exist for this turn (0 = never retried)
+    # and which one is live. The attempts themselves come from
+    # GET /actions/{id}/variants so this payload stays small.
+    variant_count: int = 0
+    variant_index: int = 0
     created_at: datetime
 
 
+class VariantOut(BaseModel):
+    index: int
+    text: str
+    reasoning: str | None = None
+    created_at: str | None = None
+    active: bool = False
+
+
+class VariantSelect(BaseModel):
+    index: int = Field(ge=0)
+
+
 class ActionUpdate(BaseModel):
     text: ActionText