v1.11: opencode-style compaction port

- compaction.ts: usable/isOverflow/estimate/turns/select/buildPrompt/process
- compaction-prompt.ts: SUMMARY_TEMPLATE verbatim from opencode
- schema: messages.{compacted_at,summary,tail_start_id} + chats.needs_compaction
- inference: auto-trigger on overflow, pre-fetch compaction before next turn
- /compact slash command rewired to new path
- WS: chat_status working/idle around compaction + compacted frame
- frontend: SummaryCard + sonner toast on compacted
- 24 unit tests for pure functions

apps/server/src/schema.sql

@@ -179,3 +179,25 @@ INSERT INTO settings (key, value) VALUES ('theme_mode', '"dark"') ON CONFLICT (k
 ALTER TABLE projects ADD COLUMN IF NOT EXISTS default_system_prompt TEXT NOT NULL DEFAULT '';
 ALTER TABLE projects ADD COLUMN IF NOT EXISTS default_web_search_enabled BOOLEAN NOT NULL DEFAULT false;
 ALTER TABLE sessions ADD COLUMN IF NOT EXISTS web_search_enabled BOOLEAN;
+
+-- v1.11: anchored rolling compaction.
+--   compacted_at  — marks rows that are "behind the curtain" of the latest
+--                   summary. Inference assembly filters compacted_at IS NULL;
+--                   the API GET still returns all rows so the UI can show
+--                   history with the summary card inline.
+--   summary       — true on the assistant row that IS the anchored summary.
+--                   Exactly one row per chat is the "current" summary
+--                   (every prior summary row is itself compacted_at-stamped
+--                   when superseded, leaving one live anchor).
+--   tail_start_id — points at the first preserved message that the summary
+--                   covers up to (exclusive). Lets the UI/debug reason about
+--                   the boundary without re-deriving from compacted_at.
+--   needs_compaction — flag on chats (not sessions) because chat history is
+--                   per-chat; sessions have 1:N chats. Set true post-overflow,
+--                   cleared by compaction.process at the start of the next
+--                   inference turn.
+ALTER TABLE messages ADD COLUMN IF NOT EXISTS compacted_at TIMESTAMPTZ;
+ALTER TABLE messages ADD COLUMN IF NOT EXISTS summary BOOLEAN NOT NULL DEFAULT FALSE;
+ALTER TABLE messages ADD COLUMN IF NOT EXISTS tail_start_id UUID REFERENCES messages(id) ON DELETE SET NULL;
+ALTER TABLE chats ADD COLUMN IF NOT EXISTS needs_compaction BOOLEAN NOT NULL DEFAULT FALSE;
+CREATE INDEX IF NOT EXISTS idx_messages_chat_compacted ON messages (chat_id, compacted_at);