chore: silence modify/delete conflicts on the deleted v1 engine

Upstream keeps patching packages/agent-core while this fork removed it
outright, so every upstream sync raised a batch of modify/delete
conflicts. Mark those paths merge=ours (driver must be enabled once per
clone) and document the one-liner in CONTRIBUTING alongside the Bun
upgrade notes.

Author: luozihao

.gitattributes

@@ -8,3 +8,10 @@
 *.gif binary
 *.ico binary
 *.png binary
+
+# Upstream keeps patching packages/agent-core (v1), which this fork deleted
+# wholesale. Keep merges auto-resolving to "deleted" instead of raising
+# modify/delete conflicts on every upstream sync. Requires the driver below
+# to be configured once per clone:
+#   git config merge.ours.driver true
+packages/agent-core/** merge=ours -diff

CONTRIBUTING.md

@@ -52,6 +52,12 @@ bun install
 > patch cache key changed from a 16 KiB hash to the full-file SHA-1. This is
 > expected, not a bug.
 
+**Syncing upstream:** this fork deletes `packages/agent-core` (the v1 engine)
+while upstream keeps patching it. `.gitattributes` marks those paths
+`merge=ours`, so merges auto-resolve to "kept deleted" instead of raising
+modify/delete conflicts. One-time setup per clone:
+`git config merge.ours.driver true`.
+
 Useful scripts:
 
 - `bun run dev:cli` — run the CLI in dev mode

CONTRIBUTING.zh-CN.md

@@ -51,6 +51,11 @@ bun install
 > `patches/ssh2@1.17.0.patch` 重新打一次：补丁缓存键已从「前 16KiB 哈希」
 > 改为整文件 SHA-1，属预期行为而非故障。
 
+**同步上游须知**：本 fork 已整体删除 `packages/agent-core`（v1 引擎），
+而上游仍在持续修补它。`.gitattributes` 已将这些路径标记为
+`merge=ours`，合并时自动保持删除态，不再产生 modify/delete 冲突。
+每个克隆需一次性执行：`git config merge.ours.driver true`。
+
 常用脚本：
 
 - `bun run dev:cli` — 开发模式运行 CLI