diff --git a/src/ir/lower.test.zig b/src/ir/lower.test.zig
index a9a9d34..956c7d5 100644
--- a/src/ir/lower.test.zig
+++ b/src/ir/lower.test.zig
@@ -1457,3 +1457,114 @@ test "lower: shadowed same-name author gets its own FuncId + real body (fix-0102
     // A name no module authors (and no flat import provides) never routes.
     try std.testing.expect(lowering.selectPlainCallableAuthor("nonexistent", b_path) == .none);
 }
+
+// E0 (R5 §#4): the scan populates the source-keyed caches partitioned by the
+// registering decl's source. Two namespaced modules each author the SAME alias
+// name `Color` AND the SAME const name `K`; the scan recurses into each
+// namespace's decls (per-source). After lowering, the by-source maps hold TWO
+// distinct entries under the two source keys (not last-wins), while the legacy
+// global maps stay single-keyed by name — the compat readers are unchanged.
+test "lower: scan populates source-keyed caches per declaring source (E0)" {
+    var arena = std.heap.ArenaAllocator.init(std.testing.allocator);
+    defer arena.deinit();
+    const alloc = arena.allocator();
+    const io = lowerTestIo();
+
+    var tmp = std.testing.tmpDir(.{});
+    defer tmp.cleanup();
+
+    try tmp.dir.writeFile(io, .{ .sub_path = "a.sx", .data = "Color :: *u8;\nK :: 5;\n" });
+    try tmp.dir.writeFile(io, .{ .sub_path = "b.sx", .data = "Color :: *u16;\nK :: 7;\n" });
+    const main_src =
+        \\na :: #import "a.sx";
+        \\nb :: #import "b.sx";
+        \\main :: () -> s32 { 0 }
+        \\
+    ;
+    try tmp.dir.writeFile(io, .{ .sub_path = "main.sx", .data = main_src });
+
+    var dirbuf: [4096]u8 = undefined;
+    const dirlen = try tmp.dir.realPath(io, &dirbuf);
+    const absdir = dirbuf[0..dirlen];
+
+    const main_path = try std.fmt.allocPrint(alloc, "{s}/main.sx", .{absdir});
+    const main_bytes = try std.Io.Dir.readFileAlloc(.cwd(), io, main_path, alloc, .limited(1 << 20));
+    const main_source = try alloc.dupeZ(u8, main_bytes);
+    var p = parser.Parser.init(alloc, main_source);
+    const root = p.parse() catch return error.ParseFailed;
+
+    var chain = std.StringHashMap(void).init(alloc);
+    var cache = imports.ModuleCache.init(alloc);
+    var import_graph = std.StringHashMap(std.StringHashMap(void)).init(alloc);
+    var flat_import_graph = std.StringHashMap(std.StringHashMap(void)).init(alloc);
+    const stdlib_paths = [_][]const u8{};
+
+    const mod = try imports.resolveImports(
+        alloc,
+        io,
+        root,
+        absdir,
+        main_path,
+        &chain,
+        &cache,
+        null,
+        null,
+        &stdlib_paths,
+        &import_graph,
+        &flat_import_graph,
+        .{},
+    );
+
+    var module_scopes = std.StringHashMap(std.StringHashMap(void)).init(alloc);
+    try module_scopes.put(main_path, mod.scope);
+    var cache_it = cache.iterator();
+    while (cache_it.next()) |entry| {
+        try module_scopes.put(entry.key_ptr.*, entry.value_ptr.scope);
+    }
+    var module_fns = imports.ModuleFns.init(alloc);
+    try imports.buildModuleFns(alloc, main_path, mod, &cache, &module_fns);
+    var facts = try imports.buildImportFacts(alloc, main_path, mod, &cache);
+
+    const resolved_root = try alloc.create(Node);
+    resolved_root.* = .{ .span = root.span, .data = .{ .root = .{ .decls = mod.decls } } };
+
+    var module = ir_mod.Module.init(alloc);
+    defer module.deinit();
+    var diagnostics = errors.DiagnosticList.init(alloc, main_source, main_path);
+    var lowering = Lowering.init(&module);
+    lowering.main_file = main_path;
+    lowering.resolved_root = resolved_root;
+    lowering.diagnostics = &diagnostics;
+    lowering.program_index.module_scopes = &module_scopes;
+    lowering.program_index.import_graph = &import_graph;
+    lowering.program_index.flat_import_graph = &flat_import_graph;
+    lowering.program_index.module_fns = &module_fns;
+    lowering.program_index.module_decls = &facts.decls;
+
+    lowering.lowerRoot(resolved_root);
+    try std.testing.expect(!diagnostics.hasErrors());
+
+    const a_path = try std.fmt.allocPrint(alloc, "{s}/a.sx", .{absdir});
+    const b_path = try std.fmt.allocPrint(alloc, "{s}/b.sx", .{absdir});
+    const idx = &lowering.program_index;
+
+    // SAME alias name `Color` lands a DISTINCT entry under each source key.
+    const color_a = idx.type_aliases_by_source.get(a_path).?.get("Color").?;
+    const color_b = idx.type_aliases_by_source.get(b_path).?.get("Color").?;
+    try std.testing.expect(color_a != color_b); // *u8 vs *u16 — source-partitioned
+
+    // SAME const name `K` lands a DISTINCT entry (distinct value node) per source.
+    const k_a = idx.module_consts_by_source.get(a_path).?.get("K").?;
+    const k_b = idx.module_consts_by_source.get(b_path).?.get("K").?;
+    try std.testing.expect(k_a.value != k_b.value);
+
+    // Compat readers: the legacy global maps stay keyed by NAME alone — a
+    // hashmap key holds exactly one value, so a same-name author is last-wins
+    // there (one entry for `Color` / `K`), unchanged by the by-source writes.
+    // The single global `Color` is one of the two source-keyed authors (not a
+    // merged/duplicated value).
+    const global_color = idx.type_alias_map.get("Color").?;
+    try std.testing.expect(global_color == color_a or global_color == color_b);
+    const global_k = idx.module_const_map.get("K").?;
+    try std.testing.expect(global_k.value == k_a.value or global_k.value == k_b.value);
+}
diff --git a/src/ir/lower.zig b/src/ir/lower.zig
index f50dcd7..e1bcd29 100644
--- a/src/ir/lower.zig
+++ b/src/ir/lower.zig
@@ -765,6 +765,31 @@ pub const Lowering = struct {
         return ti.function.call_conv != .c;
     }
 
+    // ── Source-keyed cache writers (R5 §#4) ──
+    // Mirror each global `type_alias_map` / `module_const_map` / `global_names`
+    // write into its source-partitioned analogue, keyed by the registering
+    // decl's source. Behavior-preserving for now: the global maps stay the only
+    // readers; the per-source maps exist for the later read-side cutover. A null
+    // source (unreachable for a scanned top-level decl post-import-resolution)
+    // falls back to the main file; if even that is absent the write is skipped
+    // rather than recorded under a fabricated key.
+    fn recordTypeAliasBySource(self: *Lowering, source: ?[]const u8, name: []const u8, tid: TypeId) void {
+        const src = source orelse self.main_file orelse return;
+        self.program_index.putTypeAliasBySource(src, name, tid);
+    }
+    fn recordModuleConstBySource(self: *Lowering, source: ?[]const u8, name: []const u8, info: program_index_mod.ModuleConstInfo) void {
+        const src = source orelse self.main_file orelse return;
+        self.program_index.putModuleConstBySource(src, name, info);
+    }
+    fn recordGlobalBySource(self: *Lowering, source: ?[]const u8, name: []const u8, info: program_index_mod.GlobalInfo) void {
+        const src = source orelse self.main_file orelse return;
+        self.program_index.putGlobalBySource(src, name, info);
+    }
+    fn dropModuleConstBySource(self: *Lowering, source: ?[]const u8, name: []const u8) void {
+        const src = source orelse self.main_file orelse return;
+        self.program_index.removeModuleConstBySource(src, name);
+    }
+
     /// Pass 1: Scan declarations — register ASTs and extern stubs, but don't lower bodies.
     fn scanDecls(self: *Lowering, decls: []const *const Node) void {
         // Pass 0: register every numeric-literal module const (`N :: 16` and the
@@ -785,15 +810,27 @@ pub const Lowering = struct {
             if (decl.data != .const_decl) continue;
             const cd = decl.data.const_decl;
             switch (cd.value.data) {
-                .int_literal => self.program_index.module_const_map.put(cd.name, .{ .value = cd.value, .ty = .s64 }) catch {},
-                .float_literal => self.program_index.module_const_map.put(cd.name, .{ .value = cd.value, .ty = .f64 }) catch {},
+                .int_literal => {
+                    const info = program_index_mod.ModuleConstInfo{ .value = cd.value, .ty = .s64 };
+                    self.program_index.module_const_map.put(cd.name, info) catch {};
+                    self.recordModuleConstBySource(decl.source_file, cd.name, info);
+                },
+                .float_literal => {
+                    const info = program_index_mod.ModuleConstInfo{ .value = cd.value, .ty = .f64 };
+                    self.program_index.module_const_map.put(cd.name, info) catch {};
+                    self.recordModuleConstBySource(decl.source_file, cd.name, info);
+                },
                 // A const whose RHS is an integer EXPRESSION over other consts
                 // (`M :: 2; N :: M + 1`) is itself a usable count: register it so
                 // `moduleConstInt` can fold the RHS through `evalConstIntExpr`
                 // (issue 0083). Placeholder `.s64` type — the count consumers read
                 // only the value; if the expression doesn't fold (references a
                 // non-const), `moduleConstInt` yields null and the use diagnoses.
-                .binary_op, .unary_op => self.program_index.module_const_map.put(cd.name, .{ .value = cd.value, .ty = .s64 }) catch {},
+                .binary_op, .unary_op => {
+                    const info = program_index_mod.ModuleConstInfo{ .value = cd.value, .ty = .s64 };
+                    self.program_index.module_const_map.put(cd.name, info) catch {};
+                    self.recordModuleConstBySource(decl.source_file, cd.name, info);
+                },
                 else => {},
             }
         }
@@ -877,6 +914,7 @@ pub const Lowering = struct {
                             }
                         }
                         self.program_index.type_alias_map.put(cd.name, target_ty) catch {};
+                        self.recordTypeAliasBySource(self.current_source_file, cd.name, target_ty);
                     } else if (cd.value.data == .identifier) {
                         // Identifier-RHS alias: MyAlias :: MyInt;  WideAlias :: Wide;
                         // Chase through type_alias_map, then look up named types
@@ -886,10 +924,12 @@ pub const Lowering = struct {
                         const rhs_name = cd.value.data.identifier.name;
                         if (self.program_index.type_alias_map.get(rhs_name)) |chained| {
                             self.program_index.type_alias_map.put(cd.name, chained) catch {};
+                            self.recordTypeAliasBySource(self.current_source_file, cd.name, chained);
                         } else {
                             const name_id = self.module.types.internString(rhs_name);
                             if (self.module.types.findByName(name_id)) |tid| {
                                 self.program_index.type_alias_map.put(cd.name, tid) catch {};
+                                self.recordTypeAliasBySource(self.current_source_file, cd.name, tid);
                             }
                         }
                     }
@@ -927,12 +967,14 @@ pub const Lowering = struct {
                                 const result_ty = self.resolveTypeCallWithBindings(call_data);
                                 if (result_ty != .void) {
                                     self.program_index.type_alias_map.put(cd.name, result_ty) catch {};
+                                    self.recordTypeAliasBySource(self.current_source_file, cd.name, result_ty);
                                 }
                             } else if (self.program_index.fn_ast_map.get(callee_name)) |fd| {
                                 // Type-returning function: Foo :: Complex(u32)
                                 if (fd.type_params.len > 0) {
                                     if (self.instantiateTypeFunction(cd.name, callee_name, fd, call_data.args)) |result_ty| {
                                         self.program_index.type_alias_map.put(cd.name, result_ty) catch {};
+                                        self.recordTypeAliasBySource(self.current_source_file, cd.name, result_ty);
                                     }
                                 }
                             }
@@ -961,6 +1003,7 @@ pub const Lowering = struct {
                             const result_ty = type_bridge.resolveAstType(cd.value, &self.module.types, &self.program_index.type_alias_map, &self.program_index.module_const_map);
                             if (result_ty != .void and result_ty != .unresolved) {
                                 self.program_index.type_alias_map.put(cd.name, result_ty) catch {};
+                                self.recordTypeAliasBySource(self.current_source_file, cd.name, result_ty);
                             }
                         }
                     }
@@ -974,17 +1017,19 @@ pub const Lowering = struct {
                     // stay here (their type comes from the literal / inference).
                     if (cd.type_annotation == null) {
                         // Untyped literal constants (e.g. UI_VERT_SRC :: #string GLSL...GLSL;)
-                        switch (cd.value.data) {
-                            .string_literal => self.program_index.module_const_map.put(cd.name, .{ .value = cd.value, .ty = .string }) catch {},
-                            .int_literal => self.program_index.module_const_map.put(cd.name, .{ .value = cd.value, .ty = .s64 }) catch {},
-                            .float_literal => self.program_index.module_const_map.put(cd.name, .{ .value = cd.value, .ty = .f64 }) catch {},
-                            .bool_literal => self.program_index.module_const_map.put(cd.name, .{ .value = cd.value, .ty = .bool }) catch {},
+                        const lit_ty: ?TypeId = switch (cd.value.data) {
+                            .string_literal => .string,
+                            .int_literal => .s64,
+                            .float_literal => .f64,
+                            .bool_literal => .bool,
                             // Complex constant expressions (e.g. COLOR_WHITE :: Color.{ r = 255, ... })
-                            .struct_literal => {
-                                const inferred_ty = self.inferExprType(cd.value);
-                                self.program_index.module_const_map.put(cd.name, .{ .value = cd.value, .ty = inferred_ty }) catch {};
-                            },
-                            else => {},
+                            .struct_literal => self.inferExprType(cd.value),
+                            else => null,
+                        };
+                        if (lit_ty) |ty| {
+                            const info = program_index_mod.ModuleConstInfo{ .value = cd.value, .ty = ty };
+                            self.program_index.module_const_map.put(cd.name, info) catch {};
+                            self.recordModuleConstBySource(self.current_source_file, cd.name, info);
                         }
                     }
                 },
@@ -1065,6 +1110,7 @@ pub const Lowering = struct {
         // placeholder behind as a usable const.
         if (ty == .unresolved) {
             _ = self.program_index.module_const_map.remove(cd.name);
+            self.dropModuleConstBySource(self.current_source_file, cd.name);
             return;
         }
         // Validate the initializer against the explicit annotation BY TYPE, so a
@@ -1084,6 +1130,7 @@ pub const Lowering = struct {
                 if (program_index_mod.evalConstFloatExpr(cd.value, self)) |fv| {
                     self.diagNonIntegralNarrow(cd.value.span, fv, ty);
                     _ = self.program_index.module_const_map.remove(cd.name);
+                    self.dropModuleConstBySource(self.current_source_file, cd.name);
                     return;
                 }
             }
@@ -1096,12 +1143,15 @@ pub const Lowering = struct {
             // `N : string : M + 2` are both pre-registered as `.s64` in scanDecls
             // pass 0); leaving it would let a count use still fold `N`.
             _ = self.program_index.module_const_map.remove(cd.name);
+            self.dropModuleConstBySource(self.current_source_file, cd.name);
             return;
         }
         // Reconcile the registration with the resolved annotation (pass 0 stored
         // a literal/expression placeholder type), so the const folds and emits at
         // its declared type — the same `put` the literal path always did.
-        self.program_index.module_const_map.put(cd.name, .{ .value = cd.value, .ty = ty }) catch {};
+        const info = program_index_mod.ModuleConstInfo{ .value = cd.value, .ty = ty };
+        self.program_index.module_const_map.put(cd.name, info) catch {};
+        self.recordModuleConstBySource(self.current_source_file, cd.name, info);
     }
 
     /// True iff a literal initializer of `value`'s kind is faithfully
@@ -1218,6 +1268,7 @@ pub const Lowering = struct {
             .is_extern = vd.is_foreign,
         });
         self.program_index.global_names.put(vd.name, .{ .id = gid, .ty = var_ty }) catch {};
+        self.recordGlobalBySource(self.current_source_file, vd.name, .{ .id = gid, .ty = var_ty });
     }
 
     /// Serialize a top-level global's initializer into a static `ConstantValue`.
@@ -1313,11 +1364,13 @@ pub const Lowering = struct {
                 const rhs_name = cd.value.data.identifier.name;
                 if (self.program_index.type_alias_map.get(rhs_name)) |chained| {
                     self.program_index.type_alias_map.put(cd.name, chained) catch {};
+                    self.recordTypeAliasBySource(decl.source_file, cd.name, chained);
                     progressed = true;
                 } else {
                     const name_id = self.module.types.internString(rhs_name);
                     if (self.module.types.findByName(name_id)) |tid| {
                         self.program_index.type_alias_map.put(cd.name, tid) catch {};
+                        self.recordTypeAliasBySource(decl.source_file, cd.name, tid);
                         progressed = true;
                     }
                 }
@@ -9533,6 +9586,7 @@ pub const Lowering = struct {
 
         // Register for runtime lookup: identifier resolution emits global_get
         self.program_index.global_names.put(name, .{ .id = gid, .ty = global_ty }) catch {};
+        self.recordGlobalBySource(self.current_source_file, name, .{ .id = gid, .ty = global_ty });
     }
 
     /// Lower a standalone `#run expr;` at the top level (side-effect only).
@@ -14266,6 +14320,7 @@ pub const Lowering = struct {
             .is_const = true,
         });
         self.program_index.global_names.put(global_name, .{ .id = gid, .ty = ctx_ty }) catch {};
+        self.recordGlobalBySource(self.current_source_file, global_name, .{ .id = gid, .ty = ctx_ty });
     }
 
     /// Create a thunk function: __thunk_ConcreteType_Protocol_method(ctx: *void, args...) -> ret
diff --git a/src/ir/program_index.test.zig b/src/ir/program_index.test.zig
index edaa2eb..c2ced90 100644
--- a/src/ir/program_index.test.zig
+++ b/src/ir/program_index.test.zig
@@ -97,6 +97,54 @@ test "ProgramIndex declaration maps round-trip (A1.1b)" {
     try std.testing.expectEqualStrings("list_len", idx.ufcs_alias_map.get("len").?);
 }
 
+// E0 (R5 §#4): the source-keyed caches partition by declaring source, so the
+// SAME name authored in two different modules lands two DISTINCT entries under
+// two source keys — never last-wins. The legacy global maps stay single-keyed
+// by name (one entry per name), so the compat readers are untouched.
+test "ProgramIndex source-keyed caches partition same-name authors by source" {
+    var idx = ProgramIndex.init(std.testing.allocator);
+    defer idx.deinit();
+
+    var blk_a = ast.Node{ .span = .{ .start = 0, .end = 0 }, .data = .{ .block = .{ .stmts = &.{} } } };
+    var blk_b = ast.Node{ .span = .{ .start = 1, .end = 1 }, .data = .{ .block = .{ .stmts = &.{} } } };
+
+    // SAME alias name `Foo` authored in two modules → two distinct TypeIds.
+    idx.putTypeAliasBySource("a.sx", "Foo", .s64);
+    idx.putTypeAliasBySource("b.sx", "Foo", .f64);
+    try std.testing.expectEqual(@as(?types.TypeId, .s64), idx.type_aliases_by_source.get("a.sx").?.get("Foo"));
+    try std.testing.expectEqual(@as(?types.TypeId, .f64), idx.type_aliases_by_source.get("b.sx").?.get("Foo"));
+    try std.testing.expectEqual(@as(u32, 2), idx.type_aliases_by_source.count());
+
+    // SAME const name `K` authored in two modules → two distinct ModuleConstInfos.
+    idx.putModuleConstBySource("a.sx", "K", .{ .value = &blk_a, .ty = .s32 });
+    idx.putModuleConstBySource("b.sx", "K", .{ .value = &blk_b, .ty = .f32 });
+    try std.testing.expect(idx.module_consts_by_source.get("a.sx").?.get("K").?.value == &blk_a);
+    try std.testing.expect(idx.module_consts_by_source.get("b.sx").?.get("K").?.value == &blk_b);
+    try std.testing.expectEqual(@as(?types.TypeId, .s32), idx.module_consts_by_source.get("a.sx").?.get("K").?.ty);
+    try std.testing.expectEqual(@as(?types.TypeId, .f32), idx.module_consts_by_source.get("b.sx").?.get("K").?.ty);
+
+    // SAME global name `g` authored in two modules → two distinct GlobalInfos.
+    idx.putGlobalBySource("a.sx", "g", .{ .id = inst.GlobalId.fromIndex(0), .ty = .s64 });
+    idx.putGlobalBySource("b.sx", "g", .{ .id = inst.GlobalId.fromIndex(1), .ty = .f64 });
+    try std.testing.expect(idx.globals_by_source.get("a.sx").?.get("g").?.id == inst.GlobalId.fromIndex(0));
+    try std.testing.expect(idx.globals_by_source.get("b.sx").?.get("g").?.id == inst.GlobalId.fromIndex(1));
+
+    // Compat readers: the legacy global maps stay keyed by NAME alone, so a
+    // same-name author is last-wins there — exactly ONE entry for `Foo` / `K`,
+    // unchanged by the source-keyed writes above.
+    idx.type_alias_map.put("Foo", .s64) catch unreachable;
+    idx.type_alias_map.put("Foo", .f64) catch unreachable;
+    try std.testing.expectEqual(@as(u32, 1), idx.type_alias_map.count());
+    idx.module_const_map.put("K", .{ .value = &blk_a, .ty = .s32 }) catch unreachable;
+    idx.module_const_map.put("K", .{ .value = &blk_b, .ty = .f32 }) catch unreachable;
+    try std.testing.expectEqual(@as(u32, 1), idx.module_const_map.count());
+
+    // removeModuleConstBySource drops only the named entry under its source.
+    idx.removeModuleConstBySource("a.sx", "K");
+    try std.testing.expect(idx.module_consts_by_source.get("a.sx").?.get("K") == null);
+    try std.testing.expect(idx.module_consts_by_source.get("b.sx").?.get("K").?.value == &blk_b);
+}
+
 /// Stand-in for the leaf-name lookup both array-dimension resolvers pass to the
 /// shared `evalConstIntExpr`: `M`/`N` resolve to integers, everything else is
 /// genuinely non-comptime.
diff --git a/src/ir/program_index.zig b/src/ir/program_index.zig
index 6ae2ca7..5b14896 100644
--- a/src/ir/program_index.zig
+++ b/src/ir/program_index.zig
@@ -581,6 +581,11 @@ pub const GlobalInfo = struct { id: inst.GlobalId, ty: TypeId };
 /// (set in `init`); the rest default to `page_allocator`. Written only by the
 /// declaration scan / registration code in `Lowering`; read everywhere else.
 pub const ProgramIndex = struct {
+    /// The lowering/compilation allocator (`module.alloc`), retained so the
+    /// source-keyed caches below can lazily create their inner per-source maps.
+    /// Lives for the whole compilation; the inner maps are freed in `deinit`.
+    alloc: std.mem.Allocator,
+
     // ── Import / visibility ──
     /// Declaration name → is the function imported (declared `extern`)?
     import_flags: std.StringHashMap(bool),
@@ -637,12 +642,30 @@ pub const ProgramIndex = struct {
     /// UFCS alias name → target function name.
     ufcs_alias_map: std.StringHashMap([]const u8) = std.StringHashMap([]const u8).init(std.heap.page_allocator),
 
+    // ── Source-keyed semantic caches (R5 §#4) ──
+    // The source-partitioned analogues of `type_alias_map` / `module_const_map`
+    // / `global_names`, keyed `source path → name → X`. Written by the same scan
+    // (`scanDecls` in lower.zig), keyed by the registering decl's source. The
+    // global maps above stay the ONLY readers for now; the read-side cutover to
+    // `selectedAuthor.source` lands in a later phase. These maps OWN their inner
+    // per-source maps and free them in `deinit`.
+    /// Type alias name → target TypeId, partitioned by declaring source.
+    type_aliases_by_source: std.StringHashMap(std.StringHashMap(TypeId)),
+    /// Module-level value const → info, partitioned by declaring source.
+    module_consts_by_source: std.StringHashMap(std.StringHashMap(ModuleConstInfo)),
+    /// `#run` / top-level global name → GlobalInfo, partitioned by declaring source.
+    globals_by_source: std.StringHashMap(std.StringHashMap(GlobalInfo)),
+
     pub fn init(alloc: std.mem.Allocator) ProgramIndex {
         return .{
+            .alloc = alloc,
             .import_flags = std.StringHashMap(bool).init(alloc),
             .fn_ast_map = std.StringHashMap(*const ast.FnDecl).init(alloc),
             .qualified_fn_source = std.StringHashMap([]const u8).init(alloc),
             .global_names = std.StringHashMap(GlobalInfo).init(alloc),
+            .type_aliases_by_source = std.StringHashMap(std.StringHashMap(TypeId)).init(alloc),
+            .module_consts_by_source = std.StringHashMap(std.StringHashMap(ModuleConstInfo)).init(alloc),
+            .globals_by_source = std.StringHashMap(std.StringHashMap(GlobalInfo)).init(alloc),
         };
     }
 
@@ -660,5 +683,42 @@ pub const ProgramIndex = struct {
         self.protocol_ast_map.deinit();
         self.module_const_map.deinit();
         self.ufcs_alias_map.deinit();
+        deinitBySource(TypeId, &self.type_aliases_by_source);
+        deinitBySource(ModuleConstInfo, &self.module_consts_by_source);
+        deinitBySource(GlobalInfo, &self.globals_by_source);
+    }
+
+    /// Free every inner per-source map, then the outer map.
+    fn deinitBySource(comptime V: type, outer: *std.StringHashMap(std.StringHashMap(V))) void {
+        var it = outer.valueIterator();
+        while (it.next()) |inner| inner.deinit();
+        outer.deinit();
+    }
+
+    /// Insert `name → value` into the per-source map for `source`, creating the
+    /// inner map on first use. OOM is swallowed to mirror the `catch {}` global
+    /// writes this shadows.
+    fn putBySource(comptime V: type, outer: *std.StringHashMap(std.StringHashMap(V)), alloc: std.mem.Allocator, source: []const u8, name: []const u8, value: V) void {
+        const gop = outer.getOrPut(source) catch return;
+        if (!gop.found_existing) gop.value_ptr.* = std.StringHashMap(V).init(alloc);
+        gop.value_ptr.put(name, value) catch {};
+    }
+
+    pub fn putTypeAliasBySource(self: *ProgramIndex, source: []const u8, name: []const u8, tid: TypeId) void {
+        putBySource(TypeId, &self.type_aliases_by_source, self.alloc, source, name, tid);
+    }
+
+    pub fn putModuleConstBySource(self: *ProgramIndex, source: []const u8, name: []const u8, info: ModuleConstInfo) void {
+        putBySource(ModuleConstInfo, &self.module_consts_by_source, self.alloc, source, name, info);
+    }
+
+    pub fn putGlobalBySource(self: *ProgramIndex, source: []const u8, name: []const u8, info: GlobalInfo) void {
+        putBySource(GlobalInfo, &self.globals_by_source, self.alloc, source, name, info);
+    }
+
+    /// Mirror a `module_const_map.remove` into the per-source map: drop `name`
+    /// from `source`'s inner map (a no-op if the source/name is absent).
+    pub fn removeModuleConstBySource(self: *ProgramIndex, source: []const u8, name: []const u8) void {
+        if (self.module_consts_by_source.getPtr(source)) |inner| _ = inner.remove(name);
     }
 };