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+---
+phase: quick
+plan: 1
+subsystem: inference-core, inference-server, chat-ui
+tags: [bug-fix, kv-cache, streaming, chat-history]
+dependency_graph:
+  requires: []
+  provides: [stable-multi-turn-chat, clean-error-propagation]
+  affects: [inference-core, inference-server, ChatView]
+tech_stack:
+  added: []
+  patterns: [fail-fast-on-null, empty-content-guard, history-filter]
+key_files:
+  modified:
+    - crates/inference-core/src/engine.rs
+    - crates/inference-core/src/session.rs
+    - crates/inference-server/src/routes.rs
+    - tauri-app/src/components/ChatView.tsx
+decisions:
+  - "Return Err from new_session() when llama_get_memory is NULL rather than silently continuing — prevents decode corruption on second request"
+  - "StreamItem::Error emits content:None so fullContent stays empty and is not persisted as a valid assistant message"
+  - "Assistant INSERT is guarded against empty content to avoid empty DB rows when stream fails silently"
+  - "buildApiMessages filters out empty and error-prefixed messages so corrupted history rows do not poison future context"
+metrics:
+  duration: ~10min
+  completed_date: "2026-03-30"
+  tasks: 2
+  files: 4
+---
+
+# Quick Task 1: Fix "internal error" on Second Chat Message
+
+**One-liner:** Three-layer fix for KV cache corruption causing "internal error" accumulation and DB pollution on the second chat turn.
+
+## What Was Built
+
+### Root Cause
+
+On the second request, `llama_get_memory` returns NULL on some llama.cpp builds. The previous code issued a warning and continued, leaving the KV cache from the prior session in place. The new prefill then tried to write tokens at positions already occupied, causing `llama_decode` to return non-zero. The engine propagated `StreamItem::Error`, which the frontend accumulated as real content (`"internal error"`) and saved to the DB — which then corrupted the history sent on the third request.
+
+### Fix Layer 1 — engine.rs: Fail fast on NULL KV cache
+
+`new_session()` now returns `Err` immediately when `llama_get_memory` returns NULL instead of logging a warning and continuing. This surfaces the failure as an HTTP 500 rather than a silent decode corruption.
+
+### Fix Layer 2 — session.rs: Improve prefill error diagnostic
+
+`decode_prefill` error message now includes the total token count so operators can distinguish KV cache failures from context window overflows.
+
+### Fix Layer 3 — routes.rs: StreamItem::Error emits no content
+
+`StreamItem::Error` now sends a final chunk with `content: None` instead of `content: Some("internal error")`. The frontend's `fullContent` accumulator stays empty, so nothing gets persisted to the DB.
+
+### Fix Layer 4 — ChatView.tsx: Guard assistant INSERT and filter history
+
+Two frontend fixes:
+1. `buildApiMessages` SQL excludes empty content, `⚠️ Error:` prefixed messages, and `"internal error"` rows — so any pre-existing corrupted rows do not reach the backend.
+2. The assistant `db.run(INSERT ...)` is wrapped in a guard: if `fullContent` is empty after stream completion, no row is written.
+
+## Deviations from Plan
+
+None — plan executed exactly as written. The plan prescribed four specific fixes across three files; all were applied verbatim.
+
+## Self-Check
+
+**Files exist:**
+- `crates/inference-core/src/engine.rs` — FOUND
+- `crates/inference-core/src/session.rs` — FOUND
+- `crates/inference-server/src/routes.rs` — FOUND
+- `tauri-app/src/components/ChatView.tsx` — FOUND
+
+**Commits exist:**
+- `d919879` — FOUND (Task 1: engine.rs + session.rs)
+- `44875aa` — FOUND (Task 2: routes.rs + ChatView.tsx)
+
+**Compilation:**
+- `cargo check -p inference-core -p inference-server` — PASSED
+- `npx tsc --noEmit` — PASSED
+
+**Note on test runner:** `vitest run` fails with `ERR_PACKAGE_PATH_NOT_EXPORTED` for `vite/module-runner` under Node 24 + vitest 4.1.2 + vite 5.4.x. This is a pre-existing environment incompatibility (vitest 4.x requires vite 6.x) unrelated to these changes. The test file contracts are compatible with the SQL change (`buildApiMessages` mock matches on `FROM messages WHERE chat_id = ?` which is still present in the updated query).
+
+## Self-Check: PASSED