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/migrations.py

@@ -104,6 +104,12 @@ MIGRATIONS: list[tuple[int, str]] = [
     # cards and leave player-authored ones alone. NULL = player-authored, or a
     # copy predating this column (matched by name once, then adopted).
     (33, "ALTER TABLE story_cards ADD COLUMN source_ref VARCHAR(64)"),
+    # Retry history: every attempt made for an AI turn, oldest first, so retry
+    # can append instead of deleting. NULL = never retried (the row is its own
+    # only version), which is also the correct reading for every action that
+    # predates this column.
+    (34, "ALTER TABLE actions ADD COLUMN variants JSON"),
+    (35, "ALTER TABLE actions ADD COLUMN variant_index INTEGER NOT NULL DEFAULT 0"),
 ]
 
 LATEST_VERSION = max((v for v, _ in MIGRATIONS), default=1)