docs: rename core-data-structures/ to subsystems/

The folder is becoming the home of one-doc-per-subsystem pages (intro +
data structures + cordis services/events), so the name must describe the
whole contract, not just the type-vocabulary third of it. Mechanical
rename rebuilt on current master: every inbound Markdown link, generator
constant, website route, type-equiv manifest path, and spec expectation
moves together; the zh sides of the notes whose prose names the folder
are aligned (子系统) in the same change; touched bilingual pairs
re-recorded; translation-prompt snapshot re-recorded (its example embeds
development.md). Historical Agent Note slugs keep their dated
filenames.

packages/compact/compact/README.md

@@ -24,7 +24,7 @@ All three operations are **abstract** — the backend owns trigger policy, reten
 | `compactNow(agent, signal)` | Explicitly compact one useful balanced older span even below automatic pressure. It synchronously reserves idle turn admission before yielding, writes nothing when no useful span exists, records a standalone `compact/* { turn: null }` attempt before summarization, and awaits its durability checkpoint before release. Expected operational failures use `ManualCompactionError`; cancellation rethrows the exact abort reason. |
 | `compactRegion(start, end, agent, signal?)` | Forcibly summarize surface nodes `[start, end]` (inclusive seqs) from `agent.session` into a single replacement node whose source is `COMPACT_CHECKPOINT_SOURCE`. **Throws** if a compaction is already in progress, if `start`/`end` aren't surface nodes, or if `start` is positioned after `end` on the surface. The range is a SURFACE-POSITION span, not a numeric seq interval — after a prior replace lands a fresh high-seq summary node at the shadowed range's position, surface order no longer tracks seq order. |
 
-`CompactionResult` keeps the raw summary and bookkeeping-event seqs available to callers alongside the shadowed range and token accounting; its drift-checked shape lives in the [compaction data-structure reference](../../../docs/core-data-structures/compaction.md#compactionresult).
+`CompactionResult` keeps the raw summary and bookkeeping-event seqs available to callers alongside the shadowed range and token accounting; its drift-checked shape lives in the [compaction data-structure reference](../../../docs/subsystems/compaction.md#compactionresult).
 
 `compactIfNeeded` and `compactNow` take a required `signal`; `compactRegion`'s is optional. A backend that summarizes via `ctx.llm.stream()` **must** forward it into the call's `GenerateOptions.signal`, so an abort or fiber dispose tears down the in-flight summarization. Automatic and explicit-region brackets recover their numeric owner from the currently open turn. Manual brackets require no open turn and stamp `turn: null`.