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diff --git a/backend-handoff-chat-limit.md b/backend-handoff-chat-limit.md deleted file mode 100644 index da20583..0000000 --- a/backend-handoff-chat-limit.md +++ /dev/null @@ -1,66 +0,0 @@ -# Backend handoff — CR-5: history windowing for the FE chat limit (courier doc) - -> **From:** dispatch-web · **To:** arch-rewrite · **Courier:** the user. -> Companion to the living `backend-handoff.md` (§2 CR-5). 2026-06-12. - -## Context — what the FE is building (no backend blocker) - -The FE is adding a **chat limit**: in very long conversations the transcript unloads old -chunks from memory/DOM so the browser stays fast. Policy (already decided with the user): - -- Limit `L` counts **chunks** (default 256, localStorage-configurable). -- When the loaded count exceeds `L`, the FE unloads the oldest `ceil(L/4)` chunks in ONE - bulk pass (e.g. `L=100`: at 101 chunks it unloads 25 → 76 remain). Bulk-on-threshold — - NOT one-per-delta like old Dispatch — to kill the scroll-jump-per-step failure mode. -- A fresh page load shows only the newest `floor(0.75 × L)` chunks (192 for the default). -- A "Show earlier messages" affordance pages older history back in (today: from the FE's - IndexedDB cache, which still holds it). - -**This works TODAY with no backend change** — the FE fetches everything and windows in -memory. The ask below makes the *fresh-browser* case cheap: with an empty IndexedDB cache, -`GET /conversations/:id?sinceSeq=0` currently returns the ENTIRE conversation, so a -10k-chunk chat downloads + parses megabytes only for the FE to display 192 chunks. - -## The ask (additive, `transport-contract` bump) - -Extend `GET /conversations/:id` with two OPTIONAL query params: - -1. **`limit=<n>`** — return only the **newest** `n` chunks of the selection (still - ascending seq order in the response). Selection semantics otherwise unchanged - (`seq > sinceSeq`). - - **If the selection has ≤ `n` chunks, return everything** — the FE will routinely send - a largish number (e.g. `limit=192`) against short conversations and expects the - normal full response (that flow must stay cheap and exact). - - `limit` absent → exactly today's behavior (full selection). Existing FE versions keep - working unchanged. -2. **`beforeSeq=<s>`** — restrict the selection to `seq < s` (combined with `limit`: the - newest `n` chunks below `s`, ascending). This is the "Show earlier messages" page-in - path for history the FE's local cache doesn't have (e.g. a fresh browser that - initial-loaded with `limit`). `beforeSeq` + `sinceSeq` together = `sinceSeq < seq < s` - (we only ever send one of them, but defined semantics beat undefined). - -And one additive response field on `ConversationHistoryResponse`: - -3. **`earliestSeq?: number`** (or `hasOlder: boolean` — your pick, flag your choice in the - reply) — the conversation's overall lowest seq (or whether chunks exist below the - returned window). The FE needs to know whether to OFFER "Show earlier messages" when - its local cache is exhausted. Without it the FE can only guess (seq 1 = start works if - seqs are guaranteed to start at 1 and be gap-free — if you'd rather just CONFIRM that - invariant in writing, the FE can derive `hasOlder` from `chunks[0].seq > 1` and we skip - the new field entirely; cheapest option, totally fine). - -## How the FE will consume it - -- Fresh load (empty cache): `GET /conversations/:id?sinceSeq=0&limit=<floor(0.75×L)>`. -- Incremental tail sync (cache warm): unchanged `?sinceSeq=<maxCachedSeq>` (no limit — the - tail since last sync is small by construction). -- Show-earlier beyond local cache: `GET /conversations/:id?beforeSeq=<oldestLoadedSeq>&limit=<ceil(L/4)>`. -- The FE's IndexedDB cache is seq-keyed + dedup-by-seq and already tolerates a - non-contiguous prefix (a windowed suffix), so no cache-format change is needed FE-side. - -## Priority / sequencing - -Not a blocker — the FE ships the limit feature against the current contract (full fetch + -in-memory windowing) and lights up the `limit`/`beforeSeq` params when you ship. Ship -whenever convenient; please bump `transport-contract` and note the params in the reply -handoff so the FE re-pins + re-mirrors. |