Expose actionable C# top-level symbols (#5178)

* Add actionable C# top-level symbols (#5164)

* Address top-level symbol review findings (#5164)

* Fix top-level symbol review regressions (#5164)

* Fix C# contract reuse test assumptions (#5164)

* Fix reusable snapshot performance fixture (#5164)

Author: Widthdom

DEVELOPER_GUIDE.md

@@ -1139,6 +1139,43 @@ guard that would fail before users see multi-hour indexing stalls.
 
 Do not add mutable static caches, shared `StringBuilder` instances, reused `MatchCollection` enumerators, or singleton scanner state to extractor code. If a future extractor needs cross-call memoization, use an explicit thread-safe collection and add a targeted parallel regression test that proves deterministic output under concurrent calls.
 
+### C# top-level synthetic scope contract
+
+C# extractor contract version 13 persists an actionable file-scoped symbol for
+compilation units with executable top-level statements. The symbol uses
+`kind=function`, `sub_kind=top_level_scope`, and `name=<top-level>`; public
+results derive `is_synthetic=true`, qualify the identity as
+`<indexed-path>::<top-level>`, and emit an `id:<symbol-id>@g:<generation>`
+selector. Selectors are valid only for their active index generation and are
+resolved by symbol id, so identical top-level programs in different files do
+not share callee identity.
+
+Detection runs after container assignment. It excludes declaration-covered
+ranges, imports with any legal whitespace between their C# keywords, comments,
+directives, and assembly/module metadata, recognizes
+both `using var` and explicitly typed `using Type value = ...` declarations as
+executable rather than import directives, then uses the first and last uncovered
+executable lines as both source and body bounds.
+A top-level local function remains source-declared and containerless; its own
+narrower span owns references inside the function, while a synthetic range may
+cross it when executable statements occur on both sides. When a local function
+and an outside statement share one line, declaration columns retain the local
+function while the outside statement belongs to the synthetic scope. Reference extraction
+uses the synthetic symbol's persisted id for otherwise containerless calls in
+that body. The synthetic scope is not a documented declaration, so an XML-doc
+comment before a top-level statement does not attach to it. `outline`,
+coordinate `inspect`, and identity-scoped `callees` must
+therefore navigate the same row; both CLI and MCP `callees` resolve its selector
+by persisted symbol id. Unused-symbol list and count queries exclude this
+synthetic entry point because it is executable infrastructure, not removable
+dead code. Selector-scoped callee queries fail closed when a readable legacy
+schema lacks the persisted source-identity column. If a stored C# extractor version predates this
+contract or is missing, and no synthetic row is available, outline reports
+`top_level_symbol_support=reindex_required` plus a typed limitation instead of
+claiming support. A normal full index re-extracts unchanged C# files before it
+stamps this contract, so the documented reindex remediation repairs unstamped
+legacy databases without requiring `--rebuild`.
+
 ### Symbol Kind Taxonomy
 
 `symbols.kind`, `symbols.container_kind`, and `symbol_references.container_kind` use the public symbol kind taxonomy below. New extractors must register new kind values in `SymbolKindCatalog` before writing them so schema checks, writer validation, CLI filters, and downstream JSON consumers stay aligned.
@@ -5089,6 +5126,34 @@ regression には、scope rule の focused correctness test と、ユーザー
 
 抽出器コードに mutable な static cache、共有 `StringBuilder` インスタンス、使い回しの `MatchCollection` enumerator、シングルトンの scanner state を追加してはならない。将来の抽出器が呼び出しをまたぐ memoization を必要とする場合は、明示的にスレッドセーフなコレクションを使い、並行呼び出し下でも決定的な出力になることを証明する focused な並列回帰テストを追加する。
 
+### C# top-level synthetic scope 契約
+
+C# extractor contract version 13 は、実行可能な top-level statement を持つ
+compilation unit に、操作可能な file-scoped symbol を永続化します。この symbol は
+`kind=function`、`sub_kind=top_level_scope`、`name=<top-level>` を使い、公開結果は
+`is_synthetic=true`、`<indexed-path>::<top-level>` 形式の qualified identity、
+`id:<symbol-id>@g:<generation>` 形式の selector を派生させます。selector は active な
+index generation だけで有効で、symbol id により解決するため、異なる file にある同一内容の
+top-level program が callee identity を共有することはありません。
+
+検出は container assignment の後に実行します。declaration が覆う range、C# keyword 間に
+任意の正当な whitespace を持つ import、comment、directive、assembly/module metadata を除外し、`using var` と明示型の
+`using Type value = ...` declaration の両方を import directive ではなく実行可能コードとして認識し、
+残った最初と最後の実行可能行を source/body 両方の境界にします。top-level local function は container を持たない source-declared symbol
+のままで、その function 内の reference はより狭い自身の span が所有します。両側に実行
+statement がある場合、synthetic range は local function をまたぐことがあります。local function と外側の statement が
+同じ行にある場合、宣言 column は local function が所有し、外側の statement は synthetic scope が所有します。reference
+extraction は、この body 内で従来 container を持たなかった call に synthetic symbol の永続化
+id を使います。synthetic scope は documented declaration ではないため、top-level statement
+直前の XML-doc comment を自身へ結び付けません。そのため `outline`、座標指定 `inspect`、identity-scoped `callees` は同じ row を
+navigate しなければならず、CLI / MCP の両 `callees` が selector を永続化済み symbol id で解決します。
+unused-symbol の list / count query は、この synthetic entry point が削除可能な dead code ではなく実行基盤なので除外します。
+読み取り可能な legacy schema に永続 source-identity column がない場合、selector-scoped callee query は fail-closed します。
+保存済み C# extractor version がこの契約より古いか欠落しており、
+synthetic row も無い場合、outline は対応済みと見せず、`top_level_symbol_support=reindex_required` と型付きの
+limitation を返します。通常の full index はこの contract を stamp する前に未変更 C# file も再抽出するため、
+文書化された reindex remediation は `--rebuild` なしで stamp のない legacy database を修復します。
+
 ### シンボル種別分類
 
 `symbols.kind`、`symbols.container_kind`、`symbol_references.container_kind` は

TESTING_GUIDE.md

@@ -561,6 +561,7 @@ Candidate-ordered parallel-index recovery tests must prove that the fatal result
   do not allocate production-sized 50k/20k inputs to test these contracts (#4620).
 - Broad extractor `*CompletesWithinPracticalBudget` runaway guards run only on the primary `net8.0` test target. Keep focused functional extractor tests cross-target, but do not duplicate the large-fixture budget guards across every target framework unless the guard is specifically proving a target-framework-specific contract.
 - C# reflection-name extraction coverage keeps literal, constant-concatenation, dynamic, comment, and string-decoy cases in one source fixture so those parser boundaries share one symbol/reference pass.
+- C# top-level synthetic-scope coverage (#5164) keeps the 10-line entry-point, local-function ownership including an outside call on the same line, typed using declarations, bounded extraction, legal-whitespace import directives, and all import/metadata/comment/directive/type/explicit-`Main` negatives in focused extractor fixtures. CLI reader fixtures own coordinate selection, cross-file selector isolation, caller/callee round-tripping, legacy source-identity fail-closed behavior, script-scope identity parity, compact output, stale-contract guidance, and unused list/count exclusion; the MCP assertion owns selector-to-`callees` round-tripping as well as transport naming parity. Keep full plus incremental no-op/change/add/rename/delete/no-op persistence and unstamped-C# upgrade re-extraction in `IndexCommandRunnerIssue5164Tests.cs` so lifecycle coverage uses real index reconciliation instead of direct database fixtures.
 - C# BOM extraction keeps a simple leading-BOM import fixture plus one mixed-newline fixture that simultaneously covers leading and mid-file BOM handling across CRLF, bare CR, and LF boundaries; do not repeat separate extraction passes for newline subsets already present in the mixed fixture.
 - C# lambda-capture coverage keeps positive enclosing-local capture, parameter shadowing, and same-named-method isolation in one source fixture; a single capture assertion proves the negative regions did not leak.
 - C# static-lambda declaration regression coverage keeps stateful, typed/untyped, explicit-return, both async-modifier orders, Unicode/escaped-identifier, multiline, nested, and argument-position forms in one extractor pass. Preserve real static members/local functions, including generic, constructor, explicit-interface, and verbatim-type-name forms, and an assigned-lambda range/container assertion in that fixture, plus one CLI `symbols` corpus fixture for phantom-name checks (#4830).
@@ -1685,6 +1686,7 @@ dotnet test --filter "FullyQualifiedName~GitHelperTests"
   は高負荷な C# reference extraction に対する広めの runaway guard です。C# warmup は `CI=true` かつ `net8.0` test assembly の場合だけ、各 guard が fixture 構築と stopwatch 計測より前に呼ぶ `Lazy` gate により test process ごとに1回実行します。どちらの guard も含まない shard は extraction と強制 GC の固定 warmup cost を負いません。module initializer では hook discovery の delay、persistent worker PID/thread、persistent descendant PID/process の environment 処理をこの順序のまま eager に維持してください。warmup は最後に強制 GC を行うため、この2 guard だけを専用 non-parallel collection に保ち、巨大な `ReferenceExtractorTests` partial class 全体を non-parallel にしないでください。budget は benchmark 閾値ではなく回帰 tripwire として扱い、焦点を絞った最適化根拠がない限り noisy CI に十分な余裕を残してください。
 - extractor の広い `*CompletesWithinPracticalBudget` runaway guard は primary の `net8.0` test target だけで実行します。focused な extractor 機能テストは cross-target のまま維持しますが、その guard が target-framework 固有の契約を証明する場合を除き、大規模 fixture の budget guard をすべての target framework で重複実行しないでください。
 - C# reflection-name 抽出 coverage は、literal、定数連結、dynamic、comment、string decoy を1つの source fixture にまとめ、これらの parser boundary で1回の symbol/reference pass を共有します。
+- C# top-level synthetic scope の coverage (#5164) は、10行の entry point、同じ行の外側 call を含む local-function ownership、typed using declaration、bounded extraction、正当な whitespace を持つ import directive、import / metadata / comment / directive / type / explicit `Main` の全 negative を focused extractor fixture に維持します。CLI reader fixture は座標選択、file 間の selector 分離、caller/callee round-trip、legacy source-identity の fail-closed behavior、script-scope identity parity、compact 出力、stale-contract guidance、unused list/count からの除外を担当し、MCP の assertion は transport の命名 parity に加えて selector から `callees` への round-trip を担当します。full と incremental の no-op / change / add / rename / delete / no-op 永続化、および stamp のない C# upgrade の再抽出は `IndexCommandRunnerIssue5164Tests.cs` に維持し、direct database fixture ではなく実際の index reconciliation で lifecycle を検証してください。
 - C# BOM 抽出は、単純な先頭 BOM import fixture と、CRLF・bare CR・LF 境界で先頭/mid-file BOM を同時に扱う1つの混在改行 fixture を維持します。混在 fixture に含まれる改行 subset ごとに抽出 pass を重複させないでください。
 - C# lambda capture coverage は、外側 local の正例、parameter shadowing、同名 method 間の分離を1つの source fixture にまとめます。capture が1件だけである assertion により、negative region からの漏れも同時に検証します。
 - C# static lambda の宣言回帰 coverage は、stateful、型あり/型なし、明示的戻り値型、両方の async modifier 順、Unicode/escape 識別子、複数行、入れ子、引数位置の各形式を1回の extractor pass にまとめます。同じ fixture で generic、constructor、明示的 interface、verbatim 型名を含む本物の static member / local function と、代入済み lambda の range / container assertion を維持し、phantom 名の確認には CLI `symbols` corpus fixture を1つ追加します（#4830）。