feat: unify context compaction

pi-compaction/UPSTREAM.md

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+# Upstream sources
+
+This package is maintained directly in `my-pi` and combines two separately licensed sources with a new local Context Authority.
+
+## pi-condense reference
+
+- Official repository: https://github.com/jjuraszek/pi-condense
+- Snapshot: `59c95110aacd8131db71e21296765dd80b72fae8`
+- Tag/version: `v2.9.1`
+- Used as a behavioral and summarizer-reliability reference. The new segment/index/runtime implementation is local and intentionally does not retain legacy formats.
+- License: `LICENSES/pi-condense-MIT.txt`
+
+## Pi Codex compaction source
+
+- Official repository: https://github.com/ogulcancelik/pi-extensions
+- Package path: `packages/pi-codex-compaction/`
+- Snapshot: `c4d6ca8fb484ba51684296ba8b4715f8c7b3ac91`
+- Version at snapshot: `0.1.4`
+- Imported source: remote compaction protocol, Response API conversion, retention helpers, retry parsing, and request sanitization in `src/native-compaction.ts`.
+- Local changes: unified checkpoint kind/version, removed raw-branch effective-input construction and legacy checkpoint parsing, exported the shared message projection, made retained-user budget configurable, and renamed the client user agent.
+- License: `LICENSES/pi-codex-compaction-MIT.txt`
+
+No npm tarball, npm cache, `node_modules`, build output, or nested Git metadata is used as an import source.