fix(cs-lsp): resolve nested types through type qualifiers, bind global-ns types

internal/cbm/cbm.h

@@ -246,6 +246,10 @@ typedef struct {
      * HTTP_CALLS edge to base + path. Tail fields: zero-init stays valid. */
     const char *http_client;
     const char *http_base_url;
+    /* C# only: declared namespace of a TOP-LEVEL type (NULL for nested types,
+     * the global namespace and every other language). Per type, because the
+     * file-level namespace_name records only a file's first namespace. */
+    const char *decl_namespace;
 } CBMDefinition;
 
 /* Argument captured from a call expression */

internal/cbm/extract_defs.c

@@ -4584,6 +4584,58 @@ static bool extract_sql_ddl_class_def(CBMExtractCtx *ctx, TSNode node, const cha
     return true;
 }
 
+/* Name of a C# namespace declaration node (block or file-scoped), or NULL. */
+static const char *cs_namespace_decl_name(CBMArena *a, TSNode ns, const char *source) {
+    TSNode nm = ts_node_child_by_field_name(ns, TS_FIELD("name"));
+    if (ts_node_is_null(nm)) {
+        return NULL;
+    }
+    const char *text = cbm_node_text(a, nm, source);
+    return text && text[0] ? text : NULL;
+}
+
+/* Declared namespace of a C# type declaration: every enclosing namespace
+ * block (outer to inner) under an optional file-scoped namespace, which the
+ * grammar may attach either as an ancestor or as a preceding sibling of the
+ * compilation unit's members. NULL = global namespace. The file-level
+ * namespace_name keeps only the FIRST namespace of a file, which mislabels
+ * every type of a multi-namespace file (#2120). */
+static const char *cs_type_decl_namespace(CBMArena *a, TSNode node, const char *source) {
+    const char *acc = NULL;
+    bool file_scoped = false;
+    TSNode top = node;
+    for (TSNode cur = ts_node_parent(node); !ts_node_is_null(cur); cur = ts_node_parent(cur)) {
+        const char *k = ts_node_type(cur);
+        bool is_file_scoped = strcmp(k, "file_scoped_namespace_declaration") == 0;
+        if (is_file_scoped || strcmp(k, "namespace_declaration") == 0) {
+            const char *name = cs_namespace_decl_name(a, cur, source);
+            if (name) {
+                acc = acc ? cbm_arena_sprintf(a, "%s.%s", name, acc) : name;
+            }
+            file_scoped = file_scoped || is_file_scoped;
+        }
+        top = cur;
+    }
+    if (file_scoped) {
+        return acc;
+    }
+    uint32_t start = ts_node_start_byte(node);
+    uint32_t n = ts_node_named_child_count(top);
+    for (uint32_t i = 0; i < n; i++) {
+        TSNode c = ts_node_named_child(top, i);
+        if (ts_node_start_byte(c) >= start) {
+            break;
+        }
+        if (strcmp(ts_node_type(c), "file_scoped_namespace_declaration") == 0) {
+            const char *name = cs_namespace_decl_name(a, c, source);
+            if (name) {
+                return acc ? cbm_arena_sprintf(a, "%s.%s", name, acc) : name;
+            }
+        }
+    }
+    return acc;
+}
+
 static void extract_class_def(CBMExtractCtx *ctx, TSNode node, const CBMLangSpec *spec) {
     CBMArena *a = ctx->arena;
     const char *kind = ts_node_type(node);
@@ -4951,6 +5003,9 @@ static void extract_class_def(CBMExtractCtx *ctx, TSNode node, const CBMLangSpec
     def.end_line = ts_node_end_point(node).row + TS_LINE_OFFSET;
     def.lines = (int)(def.end_line - def.start_line + TS_LINE_OFFSET);
     def.is_exported = cbm_is_exported(name, ctx->language);
+    if (ctx->language == CBM_LANG_CSHARP && !ctx->enclosing_class_qn) {
+        def.decl_namespace = cs_type_decl_namespace(a, node, ctx->source);
+    }
     def.base_classes = extract_base_classes(a, node, ctx->source, ctx->language);
     def.decorators = extract_decorators(a, node, ctx->source, ctx->language, spec);
     def.docstring = extract_docstring(a, node, ctx->source, ctx->language);

internal/cbm/lsp/cs_lsp.c

@@ -74,6 +74,8 @@ static char *cs_node_text_cached(CSLSPContext *ctx, TSNode node);
 static const CBMType *cs_unwrap_task(CSLSPContext *ctx, const CBMType *t);
 static const CBMType *cs_unwrap_nullable(const CBMType *t);
 static const char *cs_resolve_callable_value(CSLSPContext *ctx, TSNode node, TSNode *callable_leaf);
+static const char *cs_top_level_namespace(const char *type_qn, const char *short_name,
+                                          const char *module_qn, const char *namespace_name);
 
 /* ── small helpers ──────────────────────────────────────────────── */
 
@@ -356,6 +358,91 @@ static const char *cs_try_type_qn(CSLSPContext *ctx, const char *qn) {
     return NULL;
 }
 
+/* Namespaces through which `qualifier` (the part of a type reference before
+ * its simple name, NULL for a simple name) can reach a top-level type, in C#
+ * lookup order: each enclosing namespace innermost outward, then the global
+ * namespace (qualified references only) or the file's `using` namespaces
+ * (simple names only -- a using-namespace directive does not import nested
+ * namespaces). Returns the count written to `out` (at most `cap`). */
+static int cs_visible_namespaces(CSLSPContext *ctx, const char *qualifier, const char **out,
+                                 int cap) {
+    int n = 0;
+    const char *ns = ctx->namespace_count > 0 ? cs_namespace_qn(ctx) : NULL;
+    while (ns && *ns && n < cap) {
+        out[n++] = qualifier ? cbm_arena_sprintf(ctx->arena, "%s.%s", ns, qualifier) : ns;
+        const char *dot = strrchr(ns, '.');
+        ns = dot ? cbm_arena_strndup(ctx->arena, ns, (size_t)(dot - ns)) : NULL;
+    }
+    if (qualifier) {
+        if (n < cap)
+            out[n++] = qualifier;
+        return n;
+    }
+    for (int i = 0; i < ctx->using_count && n < cap; i++) {
+        const CBMCSUsing *u = &ctx->usings[i];
+        if (u->kind == CBM_CS_USING_NAMESPACE && u->target_qn && u->target_qn[0])
+            out[n++] = u->target_qn;
+    }
+    /* The global namespace is checked last: an unqualified name binds to a
+     * top-level type declared without a namespace whatever the file imports
+     * (#2120 residual — such types used to be invisible to step 8b). */
+    if (n < cap)
+        out[n++] = "";
+    return n;
+}
+
+/* Bind a (possibly namespace-qualified) type reference to the project type
+ * whose DECLARED namespace the current file can see, preferring the earliest
+ * namespace in C# lookup order; equal ranks keep registration order. NULL when
+ * no top-level type with that simple name is visible (#2120). */
+static const char *cs_resolve_by_declared_namespace(CSLSPContext *ctx, const char *name) {
+    if (!ctx->registry || !name || !*name)
+        return NULL;
+    const char *simple = cs_short_name(name);
+    if (!simple || !*simple)
+        return NULL;
+    const char *qualifier =
+        simple > name ? cbm_arena_strndup(ctx->arena, name, (size_t)(simple - name - 1)) : NULL;
+    enum { CS_VISIBLE_NS_MAX = 128 };
+    const char *visible[CS_VISIBLE_NS_MAX];
+    int visible_count = cs_visible_namespaces(ctx, qualifier, visible, CS_VISIBLE_NS_MAX);
+    if (visible_count == 0)
+        return NULL;
+
+    const CBMRegisteredType *best = NULL;
+    int best_rank = visible_count;
+    CBMTypeShortIter it;
+    cbm_registry_types_by_short_name_chain(ctx->registry, simple, &it);
+    int i;
+    while ((i = cbm_type_short_iter_next(&it)) >= 0) {
+        const CBMRegisteredType *cand = &it.reg->types[i];
+        if (!cand->namespace_qn || !cand->short_name || strcmp(cand->short_name, simple) != 0)
+            continue;
+        for (int r = 0; r < best_rank; r++) {
+            if (strcmp(cand->namespace_qn, visible[r]) == 0) {
+                best = cand;
+                best_rank = r;
+                break;
+            }
+        }
+    }
+    /* No namespace-qualified hit: a qualified `A.B` may name a NESTED type —
+     * A a type in scope (resolved recursively, one segment shorter), B a
+     * member type of it. Nested QNs are the parent QN plus the simple name,
+     * which step 8b's namespace scan can never produce because nested types
+     * carry no namespace_qn (#2120 residual: `new Command.Result(...)`,
+     * `new Grain.Handler(dep).Handle(...)`). */
+    if (!best && qualifier) {
+        const char *qtype = cs_resolve_type_name(ctx, qualifier);
+        if (qtype) {
+            const char *nested = cbm_arena_sprintf(ctx->arena, "%s.%s", qtype, simple);
+            if (cs_lookup_type_qn(ctx, nested))
+                return nested;
+        }
+    }
+    return best ? best->qualified_name : NULL;
+}
+
 /* Returns a fully-qualified type name resolved against:
  *   1. predefined alias (int -> System.Int32)
  *   2. type-parameter substitution map
@@ -365,7 +452,9 @@ static const char *cs_try_type_qn(CSLSPContext *ctx, const char *qn) {
  *   6. module-prefixed (file-local QN that the unified extractor produced)
  *   7. each `using namespace X` prefix
  *   8. each `using A = X` alias substitution
- *   9. fall back to bare name (registry will fail; pipeline drops the call)
+ *   8b. declared namespace of a top-level project type (enclosing namespaces,
+ *       then `using` namespaces)
+ *   9. short-name fallback, then the bare name (registry miss drops the call)
  */
 const char *cs_resolve_type_name(CSLSPContext *ctx, const char *raw) {
     if (!raw || !*raw)
@@ -457,6 +546,11 @@ const char *cs_resolve_type_name(CSLSPContext *ctx, const char *raw) {
                 char *target_bare = cs_strip_generic_args(ctx->arena, u->target_qn);
                 if (target_bare && cs_lookup_type_qn(ctx, target_bare))
                     return target_bare;
+                /* A project type is registered under its path-derived QN, so
+                 * `using A = Ns.Type;` binds through the declared namespace. */
+                const char *declared = cs_resolve_by_declared_namespace(ctx, target_bare);
+                if (declared)
+                    return declared;
                 return cbm_arena_strdup(ctx->arena, u->target_qn);
             }
             if (bare[alias_len] == '.') {
@@ -470,6 +564,15 @@ const char *cs_resolve_type_name(CSLSPContext *ctx, const char *raw) {
         }
     }
 
+    /* 8b. Declared-namespace binding for project types (#2120): their QNs are
+     * path-derived, so steps 5 and 7 cannot hit them; bind by the namespace
+     * each top-level type declares, in C# lookup order. */
+    {
+        const char *declared = cs_resolve_by_declared_namespace(ctx, bare);
+        if (declared)
+            return declared;
+    }
+
     /* 9. Short-name fallback: scan the registry for any type whose
      * short_name equals `bare` and whose QN shares the longest namespace
      * prefix with the file's namespace stack. This recovers cross-file
@@ -525,6 +628,28 @@ const char *cs_resolve_type_name(CSLSPContext *ctx, const char *raw) {
     return bare;
 }
 
+/* Other top-level declarations of the type `t` names: same simple name, same
+ * declared namespace, different entry. Registration order; at most `cap`. */
+static int cs_namespace_twins(CSLSPContext *ctx, const CBMRegisteredType *t,
+                              const CBMRegisteredType **out, int cap) {
+    if (!ctx->registry || !t || !t->namespace_qn || !t->short_name)
+        return 0;
+    int n = 0;
+    CBMTypeShortIter it;
+    cbm_registry_types_by_short_name_chain(ctx->registry, t->short_name, &it);
+    int i;
+    while (n < cap && (i = cbm_type_short_iter_next(&it)) >= 0) {
+        const CBMRegisteredType *c = &it.reg->types[i];
+        if (!c->namespace_qn || !c->short_name || !c->qualified_name ||
+            strcmp(c->short_name, t->short_name) != 0 ||
+            strcmp(c->namespace_qn, t->namespace_qn) != 0 ||
+            strcmp(c->qualified_name, t->qualified_name) == 0)
+            continue;
+        out[n++] = c;
+    }
+    return n;
+}
+
 /* Look up a method on a type, walking inheritance chain. */
 const CBMRegisteredFunc *cs_lookup_method(CSLSPContext *ctx, const char *type_qn,
                                           const char *method_name) {
@@ -535,19 +660,34 @@ const CBMRegisteredFunc *cs_lookup_method(CSLSPContext *ctx, const char *type_qn
     if (f)
         return f;
 
-    /* Walk inheritance chain (base + interfaces + transitive bases). */
     const CBMRegisteredType *t = cs_lookup_type_qn(ctx, type_qn);
     if (!t)
         return NULL;
 
+    /* The other declarations of this same type -- `partial` pieces in other
+     * files, reference-assembly copies -- are separate registry entries
+     * (path-derived QNs) but one C# type: a member declared on any of them is
+     * a member of this one, and so is a base declared on any of them. */
+    const CBMRegisteredType *twins[CS_LSP_PARENT_WALK_MAX] = {0};
+    int twin_count = cs_namespace_twins(ctx, t, twins, CS_LSP_PARENT_WALK_MAX);
+    for (int k = 0; k < twin_count; k++) {
+        f = cbm_registry_lookup_method(ctx->registry, twins[k]->qualified_name, method_name);
+        if (f)
+            return f;
+    }
+
+    /* Walk inheritance chain (base + interfaces + transitive bases). */
     const char *visited[CS_LSP_PARENT_WALK_MAX];
     int visited_count = 0;
     const char *frontier[CS_LSP_PARENT_WALK_MAX];
     int frontier_count = 0;
 
-    if (t->embedded_types) {
-        for (int i = 0; t->embedded_types[i] && frontier_count < CS_LSP_PARENT_WALK_MAX; i++) {
-            frontier[frontier_count++] = t->embedded_types[i];
+    for (int k = -1; k < twin_count; k++) {
+        const CBMRegisteredType *decl = k < 0 ? t : twins[k];
+        for (int i = 0; decl->embedded_types && decl->embedded_types[i] &&
+                        frontier_count < CS_LSP_PARENT_WALK_MAX;
+             i++) {
+            frontier[frontier_count++] = decl->embedded_types[i];
         }
     }
 
@@ -3469,6 +3609,8 @@ void cbm_run_cs_lsp(CBMArena *arena, CBMFileResult *result, const char *source,
             memset(&rt, 0, sizeof(rt));
             rt.qualified_name = d->qualified_name;
             rt.short_name = d->name;
+            rt.namespace_qn =
+                cs_top_level_namespace(d->qualified_name, d->name, module_qn, d->decl_namespace);
             rt.is_interface = (strcmp(d->label, "Interface") == 0);
             if (d->base_classes) {
                 int bc = 0;
@@ -3620,6 +3762,24 @@ void cbm_run_cs_lsp(CBMArena *arena, CBMFileResult *result, const char *source,
 
 /* ── cross-file entry ───────────────────────────────────────────── */
 
+/* The type's declared `namespace_name` when `type_qn` is a TOP-LEVEL type of
+ * the file whose module QN is `module_qn` (top-level C# type QNs are exactly
+ * module.Name; nested ones are module.Outer.Name and stay NULL, since a nested
+ * type is not reachable by its simple name through a namespace). */
+static const char *cs_top_level_namespace(const char *type_qn, const char *short_name,
+                                          const char *module_qn, const char *namespace_name) {
+    if (!type_qn || !short_name || !module_qn)
+        return NULL;
+    size_t mlen = strlen(module_qn);
+    if (strncmp(type_qn, module_qn, mlen) != 0 || type_qn[mlen] != '.' ||
+        strcmp(type_qn + mlen + 1, short_name) != 0)
+        return NULL;
+    /* Top-level C# type: its declared namespace, "" when it declares none
+     * (global namespace) so step 8b can bind it — NULL stays reserved for
+     * nested types, which no namespace can reach by simple name. */
+    return (namespace_name && namespace_name[0]) ? namespace_name : "";
+}
+
 /* Register one batch of CBMLSPDef[] into a registry. Shared by the
  * per-file cross-LSP path and the Tier 2 pre-built registry builder.
  * Def-driven (no per-file AST mutation) so deterministic per def set. */
@@ -3636,6 +3796,8 @@ static void cs_register_lsp_defs(CBMArena *arena, CBMTypeRegistry *reg, CBMLSPDe
             memset(&rt, 0, sizeof(rt));
             rt.qualified_name = d->qualified_name;
             rt.short_name = d->short_name;
+            rt.namespace_qn = cs_top_level_namespace(d->qualified_name, d->short_name,
+                                                     d->def_module_qn, d->namespace_name);
             rt.is_interface = d->is_interface || (strcmp(d->label, "Interface") == 0);
             if (d->embedded_types && *d->embedded_types) {
                 /* Parse "|"-separated list. */

internal/cbm/lsp/type_registry.h

@@ -64,6 +64,12 @@ typedef struct {
     const CBMType *index_value_type; // V or NULL
     // Generic constraints, parallel to type_param_names. NULL or shorter array means "any".
     const CBMType **type_param_constraints; // NULL-terminated, parallel to type_param_names
+
+    // --- C#-specific (NULL for every other language) ---
+    // Declared namespace of a TOP-LEVEL project type. Graph QNs are path-derived,
+    // so this is the only way to bind a short name through `using` directives and
+    // enclosing namespaces (#2120). NULL for nested types and unknown namespaces.
+    const char *namespace_qn;
 } CBMRegisteredType;
 
 // Hash-table bucket entry. Chains collisions via next-index list for overload sets.

internal/cbm/result_compact.c

@@ -275,6 +275,7 @@ static void cr_walk_def(cr_ctx_t *c, CBMDefinition *d) {
     cr_str(c, &d->impl_trait);
     cr_str(c, &d->http_client);
     cr_str(c, &d->http_base_url);
+    cr_str(c, &d->decl_namespace);
 }
 
 static void cr_walk_call(cr_ctx_t *c, CBMCall *call) {

src/pipeline/pass_lsp_cross.c

@@ -409,6 +409,12 @@ static int pxc_build_lsp_def(CBMArena *arena, const CBMDefinition *src, const ch
     dst->label = label;
     dst->def_module_qn = module_qn;
     dst->namespace_name = namespace_name ? cbm_arena_strdup(arena, namespace_name) : NULL;
+    /* C# types carry their OWN declared namespace: the file-level one is only
+     * the file's first namespace, wrong for every later namespace (#2120). */
+    if (lang == CBM_LANG_CSHARP && cbm_label_is_type_like(src->label)) {
+        dst->namespace_name =
+            src->decl_namespace ? cbm_arena_strdup(arena, src->decl_namespace) : NULL;
+    }
     dst->is_interface = (strcmp(label, "Interface") == 0 || strcmp(label, "Protocol") == 0);
     /* Single return-type string. The per-language registrars split on '|'
      * for multi-return languages (Go); single-return languages just see one

src/pipeline/pipeline.c

@@ -1194,7 +1194,8 @@ static void log_result_census(const char *tag, CBMFileResult **cache, int file_c
             }
             str_def_fp += def->fingerprint ? (size_t)def->fingerprint_k * sizeof(uint32_t) : 0;
             str_def_misc += census_len(def->route_path) + census_len(def->route_method) +
-                            census_len(def->impl_trait) + census_len(def->http_base_url);
+                            census_len(def->impl_trait) + census_len(def->http_base_url) +
+                            census_len(def->decl_namespace);
         }
         for (int c = 0; c < r->calls.count; c++) {
             const CBMCall *call = &r->calls.items[c];