fix: opencode plugin install/remove preserves foreign entries verbatim (#1002)

[ranxianglei]

Fixes #1002

What

bili plugin install/remove opencode was lossy on foreign plugin entries:

1. Install rewrite — pluginEntries() projected the raw value to strings only, and that projection was written back. Object entries ({package, options}) silently vanished; map-form plugins collapsed to bare keys.
2. "plugin present" lied — the early-return fired after write(), so an idempotent install still rewrote (and mangled) the key.
3. Remove rewrite — same strings-only projection, plus the key was deleted when no string survived: an array holding one object entry + ours lost the whole key.
4. Stale backup — .bili-bak was written once ever (first write), so it quickly stopped representing any recoverable state.

Fix

• applyOpencodePluginEntry operates on the raw value: foreign entries (objects, map forms, odd scalars) are preserved verbatim in form and position; only our own entries are added/removed. "plugin present" short-circuits before any write (idempotent install = byte-identical file).
• opencodeRemove drops the key only when nothing raw survives, and keeps map form.
• Backup discipline: re-snapshot on every write whose pre-write bytes differ from bili's own last output (.bili-last sidecar hash). User edits refresh the backup; bili's consecutive writes do not — so the install→upgrade→remove compaction-restore chain still yields the user's pre-install value, while a user edit between bili writes is never lost from the backup.
• codex/omp write paths funnel through the same writeConfigText discipline.

Tests

• tests/issue1002-opencode-foreign-entries.test.ts (new): array objects + map forms survive install AND remove; key kept when only objects remain; "plugin present" leaves the file byte-identical; backup reflects the latest user-edited state.
• Updated the two tests that asserted the old lossy behavior as contract (non-string entries ignored, version-map normalized to keys) — they now assert preservation.
• npm run typecheck ✅ · npm test 1965 pass / 0 fail (2 e2e-gated skips) ✅ · npm run build ✅

Notes

• JSONC targets: when we do modify the plugins key, its value span is re-serialized (values survive; a comment inside that span would not). Pre-existing plugin install opencode 写 V1 键名 plugin 到新建的 opencode.json：2.x 下该行无效（靠目录自动发现兜住），且与用户 opencode.jsonc 配置分裂 #927 tradeoff, unchanged.
• Ship vehicle: intended for v0.1.125 together with fix: single-writer plugin guard — never overwrite host-managed copies (#991) #995 per the release plan in [Bug] bili plugin install/remove opencode 会静默删除 plugins 数组里的对象形态条目（{package, options} 一起丢） #1002/native模式下自动更新问题需要解决 #991 discussion.

[github-actions]

📦 Built Package Artifact

Branch: 2026-09-19_opencode-plugin-preserve (d052bbf)

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1. Download the artifact from the Actions run
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tar xzf billion-context-pr1005.tgz
npm install -g package

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