diff --git a/src/diagnostics.zig b/src/diagnostics.zig
index a91d2a6..7924e3d 100644
--- a/src/diagnostics.zig
+++ b/src/diagnostics.zig
@@ -1,4 +1,5 @@
 const std = @import("std");
+const lsp = @import("lsp.zig");
 
 // Local v1 guardrails for SSH/iPhone use: visible rows instead of silent stalls.
 // req: testing/001, testing/002, testing/003, testing/004
@@ -7,6 +8,27 @@ pub const max_search_rows: usize = 64;
 pub const process_stdout_limit: usize = 256 * 1024;
 pub const process_stderr_limit: usize = 256 * 1024;
 
+pub const SourceLabel = struct {
+    provider: ?[]const u8,
+    row: []const u8,
+};
+
+pub fn sourceLabel(row: []const u8) SourceLabel {
+    if (std.mem.startsWith(u8, row, "provider:")) {
+        return .{
+            .provider = lsp.providerIdFromRow(row) catch null,
+            .row = lsp.providerPayloadFromRow(row) catch row,
+        };
+    }
+    return .{ .provider = null, .row = row };
+}
+
+pub fn displayRowAlloc(allocator: std.mem.Allocator, row: []const u8) ![]u8 {
+    const labelled = sourceLabel(row);
+    if (labelled.provider) |provider| return std.fmt.allocPrint(allocator, "[{s}] {s}", .{ provider, labelled.row });
+    return allocator.dupe(u8, labelled.row);
+}
+
 pub fn searchTruncatedRowAlloc(allocator: std.mem.Allocator, shown: usize, limit: usize) ![]u8 {
     return std.fmt.allocPrint(allocator, "diagnostic:search_truncated:showing_{d}_of_limit_{d}", .{ shown, limit });
 }
@@ -46,3 +68,19 @@ test "adversarial: unsafe diagnostic reasons are sanitized" {
     try std.testing.expectEqualStrings("unknown", sanitizeReason(""));
     try std.testing.expectEqualStrings("spawn_error", sanitizeReason("spawn_error"));
 }
+
+test "regular: provider-labelled diagnostic rows display source identity" {
+    const labelled = sourceLabel("provider:zls:diagnostic:error:boom");
+    try std.testing.expectEqualStrings("zls", labelled.provider.?);
+    try std.testing.expectEqualStrings("diagnostic:error:boom", labelled.row);
+
+    const display = try displayRowAlloc(std.testing.allocator, "provider:zls:diagnostic:error:boom");
+    defer std.testing.allocator.free(display);
+    try std.testing.expectEqualStrings("[zls] diagnostic:error:boom", display);
+}
+
+test "regular: unlabelled diagnostic rows stay compatible" {
+    const labelled = sourceLabel("diagnostic:error:boom");
+    try std.testing.expect(labelled.provider == null);
+    try std.testing.expectEqualStrings("diagnostic:error:boom", labelled.row);
+}
diff --git a/src/lsp.zig b/src/lsp.zig
index 10adc64..1a069c7 100644
--- a/src/lsp.zig
+++ b/src/lsp.zig
@@ -19,8 +19,162 @@ pub const Error = error{
     InvalidEdit,
     InvalidEditRow,
     InvalidHelp,
+    DuplicateProvider,
+    InvalidProvider,
+    MissingProvider,
+    AmbiguousProvider,
 };
 
+pub const ProviderKind = enum {
+    lsp,
+    linter,
+    formatter,
+    build,
+    test_runner,
+    checker,
+};
+
+pub const ProviderCapability = enum {
+    diagnostics,
+    hover,
+    signature,
+    navigation,
+    format,
+    code_action,
+    lint,
+    build,
+    tests,
+    check,
+    rename,
+    organize_imports,
+};
+
+pub const Provider = struct {
+    id: []const u8,
+    name: []const u8,
+    kind: ProviderKind,
+    capabilities: []const ProviderCapability,
+    preferred_for_mutation: bool = false,
+    document_version: u64 = 0,
+    alive: bool = true,
+
+    pub fn supports(self: Provider, capability: ProviderCapability) bool {
+        for (self.capabilities) |candidate| if (candidate == capability) return true;
+        return false;
+    }
+};
+
+pub const ProviderChoice = union(enum) {
+    missing,
+    selected: Provider,
+    ambiguous: []Provider,
+};
+
+pub const ProviderRegistry = struct {
+    allocator: std.mem.Allocator,
+    providers: std.ArrayList(Provider),
+
+    pub fn init(allocator: std.mem.Allocator) ProviderRegistry {
+        return .{ .allocator = allocator, .providers = .empty };
+    }
+
+    pub fn deinit(self: *ProviderRegistry) void {
+        self.providers.deinit(self.allocator);
+        self.* = undefined;
+    }
+
+    pub fn register(self: *ProviderRegistry, provider: Provider) !void {
+        if (provider.id.len == 0 or provider.name.len == 0) return Error.InvalidProvider;
+        for (self.providers.items) |existing| {
+            if (std.mem.eql(u8, existing.id, provider.id)) return Error.DuplicateProvider;
+        }
+        try self.providers.append(self.allocator, provider);
+    }
+
+    pub fn nonMutatingProvidersAlloc(self: *const ProviderRegistry, allocator: std.mem.Allocator, capability: ProviderCapability) ![]Provider {
+        var matches = std.ArrayList(Provider).empty;
+        errdefer matches.deinit(allocator);
+        for (self.providers.items) |provider| {
+            if (provider.alive and provider.supports(capability)) try matches.append(allocator, provider);
+        }
+        return matches.toOwnedSlice(allocator);
+    }
+
+    pub fn chooseMutatingProvider(self: *const ProviderRegistry, allocator: std.mem.Allocator, capability: ProviderCapability) !ProviderChoice {
+        const matches = try self.nonMutatingProvidersAlloc(allocator, capability);
+        if (matches.len == 0) {
+            allocator.free(matches);
+            return .missing;
+        }
+        var preferred: ?Provider = null;
+        for (matches) |provider| if (provider.preferred_for_mutation) {
+            if (preferred != null) return .{ .ambiguous = matches };
+            preferred = provider;
+        };
+        if (preferred) |provider| {
+            allocator.free(matches);
+            return .{ .selected = provider };
+        }
+        if (matches.len == 1) {
+            const provider = matches[0];
+            allocator.free(matches);
+            return .{ .selected = provider };
+        }
+        return .{ .ambiguous = matches };
+    }
+
+    pub fn isStale(self: *const ProviderRegistry, provider_id: []const u8, document_version: u64) !bool {
+        for (self.providers.items) |provider| {
+            if (std.mem.eql(u8, provider.id, provider_id)) return document_version < provider.document_version;
+        }
+        return Error.MissingProvider;
+    }
+};
+
+pub fn providerRowsAlloc(allocator: std.mem.Allocator, provider: Provider, rows: []const []const u8) ![][]const u8 {
+    var labelled = std.ArrayList([]const u8).empty;
+    errdefer {
+        for (labelled.items) |row| allocator.free(row);
+        labelled.deinit(allocator);
+    }
+    for (rows) |row| {
+        try labelled.append(allocator, try std.fmt.allocPrint(allocator, "provider:{s}:{s}", .{ provider.id, row }));
+    }
+    return labelled.toOwnedSlice(allocator);
+}
+
+pub fn providerIdFromRow(row: []const u8) ![]const u8 {
+    if (!std.mem.startsWith(u8, row, "provider:")) return Error.InvalidProvider;
+    const rest = row[9..];
+    const split = std.mem.indexOfScalar(u8, rest, ':') orelse return Error.InvalidProvider;
+    if (split == 0) return Error.InvalidProvider;
+    return rest[0..split];
+}
+
+pub fn providerPayloadFromRow(row: []const u8) ![]const u8 {
+    if (!std.mem.startsWith(u8, row, "provider:")) return Error.InvalidProvider;
+    const rest = row[9..];
+    const split = std.mem.indexOfScalar(u8, rest, ':') orelse return Error.InvalidProvider;
+    if (split == 0 or split + 1 > rest.len) return Error.InvalidProvider;
+    return rest[split + 1 ..];
+}
+
+pub fn missingProviderRowAlloc(allocator: std.mem.Allocator, capability: ProviderCapability) ![]const u8 {
+    return std.fmt.allocPrint(allocator, "provider:missing:{s}", .{@tagName(capability)});
+}
+
+pub fn providerPickerRowsAlloc(allocator: std.mem.Allocator, capability: ProviderCapability, providers: []const Provider) ![][]const u8 {
+    var rows = std.ArrayList([]const u8).empty;
+    errdefer {
+        for (rows.items) |row| allocator.free(row);
+        rows.deinit(allocator);
+    }
+    for (providers) |provider| {
+        try rows.append(allocator, try std.fmt.allocPrint(allocator, "provider:choose:{s}:{s}:{s}", .{ @tagName(capability), provider.id, provider.name }));
+    }
+    return rows.toOwnedSlice(allocator);
+}
+
 pub const Document = struct {
     uri: []const u8,
     language_id: []const u8,
@@ -985,3 +1139,118 @@ test "adversarial: help payloads and non-call parameter moves fail safely" {
     try std.testing.expectEqualStrings("lsp:param:outside_call", moved.rows[0]);
     try std.testing.expectEqual(@as(usize, 3), moved.cursor);
 }
+
+test "regular: provider registry preserves source identity for non-mutating rows" {
+    var registry = ProviderRegistry.init(std.testing.allocator);
+    defer registry.deinit();
+    const caps = [_]ProviderCapability{ .diagnostics, .hover };
+    try registry.register(.{ .id = "zls", .name = "ZLS", .kind = .lsp, .capabilities = &caps, .document_version = 4 });
+    try registry.register(.{ .id = "lint", .name = "Lint", .kind = .linter, .capabilities = &[_]ProviderCapability{.diagnostics}, .document_version = 4 });
+
+    const providers = try registry.nonMutatingProvidersAlloc(std.testing.allocator, .diagnostics);
+    defer std.testing.allocator.free(providers);
+    try std.testing.expectEqual(@as(usize, 2), providers.len);
+
+    const rows_src = [_][]const u8{"lsp:diag:error:1:1:file.zig:bad"};
+    const rows = try providerRowsAlloc(std.testing.allocator, providers[0], &rows_src);
+    defer {
+        for (rows) |row| std.testing.allocator.free(row);
+        std.testing.allocator.free(rows);
+    }
+    try std.testing.expectEqualStrings("provider:zls:lsp:diag:error:1:1:file.zig:bad", rows[0]);
+    try std.testing.expectEqualStrings("zls", try providerIdFromRow(rows[0]));
+    try std.testing.expectEqualStrings("lsp:diag:error:1:1:file.zig:bad", try providerPayloadFromRow(rows[0]));
+}
+
+test "regular: mutating provider choice defaults to preferred or reports ambiguity" {
+    var registry = ProviderRegistry.init(std.testing.allocator);
+    defer registry.deinit();
+    try registry.register(.{ .id = "fmt-a", .name = "Formatter A", .kind = .formatter, .capabilities = &[_]ProviderCapability{.format} });
+    try registry.register(.{ .id = "fmt-b", .name = "Formatter B", .kind = .formatter, .capabilities = &[_]ProviderCapability{.format} });
+
+    var choice = try registry.chooseMutatingProvider(std.testing.allocator, .format);
+    switch (choice) {
+        .ambiguous => |providers| {
+            defer std.testing.allocator.free(providers);
+            try std.testing.expectEqual(@as(usize, 2), providers.len);
+            const picker = try providerPickerRowsAlloc(std.testing.allocator, .format, providers);
+            defer {
+                for (picker) |row| std.testing.allocator.free(row);
+                std.testing.allocator.free(picker);
+            }
+            try std.testing.expectEqualStrings("provider:choose:format:fmt-a:Formatter A", picker[0]);
+        },
+        else => return error.ExpectedAmbiguousProvider,
+    }
+
+    var preferred = ProviderRegistry.init(std.testing.allocator);
+    defer preferred.deinit();
+    try preferred.register(.{ .id = "fmt-a", .name = "Formatter A", .kind = .formatter, .capabilities = &[_]ProviderCapability{.format}, .preferred_for_mutation = true });
+    try preferred.register(.{ .id = "fmt-b", .name = "Formatter B", .kind = .formatter, .capabilities = &[_]ProviderCapability{.format} });
+    choice = try preferred.chooseMutatingProvider(std.testing.allocator, .format);
+    switch (choice) {
+        .selected => |provider| try std.testing.expectEqualStrings("fmt-a", provider.id),
+        else => return error.ExpectedSelectedProvider,
+    }
+}
+
+test "adversarial: provider registry rejects duplicates reports missing and stale" {
+    var registry = ProviderRegistry.init(std.testing.allocator);
+    defer registry.deinit();
+    try registry.register(.{ .id = "zls", .name = "ZLS", .kind = .lsp, .capabilities = &[_]ProviderCapability{.diagnostics}, .document_version = 7 });
+    try std.testing.expectError(Error.DuplicateProvider, registry.register(.{ .id = "zls", .name = "Other", .kind = .lsp, .capabilities = &[_]ProviderCapability{.hover} }));
+
+    const missing_choice = try registry.chooseMutatingProvider(std.testing.allocator, .format);
+    switch (missing_choice) {
+        .missing => {},
+        else => return error.ExpectedMissingProvider,
+    }
+    const missing_row = try missingProviderRowAlloc(std.testing.allocator, .format);
+    defer std.testing.allocator.free(missing_row);
+    try std.testing.expectEqualStrings("provider:missing:format", missing_row);
+
+    try std.testing.expect(try registry.isStale("zls", 6));
+    try std.testing.expect(!(try registry.isStale("zls", 7)));
+    try std.testing.expectError(Error.MissingProvider, registry.isStale("none", 1));
+}
+
+test "regular: provider-labelled diagnostic rows retain original parser compatibility" {
+    const payload =
+        \\{"params":{"uri":"file:///a.zig","diagnostics":[{"range":{"start":{"line":0,"character":2}},"severity":1,"message":"boom"}]}}
+    ;
+    const rows = try diagnosticRowsAlloc(std.testing.allocator, payload);
+    defer {
+        for (rows) |row| std.testing.allocator.free(row);
+        std.testing.allocator.free(rows);
+    }
+    const provider: Provider = .{ .id = "zls", .name = "ZLS", .kind = .lsp, .capabilities = &[_]ProviderCapability{.diagnostics} };
+    const labelled = try providerRowsAlloc(std.testing.allocator, provider, rows[1..]);
+    defer {
+        for (labelled) |row| std.testing.allocator.free(row);
+        std.testing.allocator.free(labelled);
+    }
+    const payload_row = try providerPayloadFromRow(labelled[0]);
+    const location = try diagnosticLocationFromRow(payload_row);
+    try std.testing.expectEqual(@as(usize, 1), location.line);
+    try std.testing.expectEqual(@as(usize, 3), location.character);
+}
+
+test "regular: provider rows label hover signature navigation actions and lint uniformly" {
+    const provider: Provider = .{ .id = "zls", .name = "ZLS", .kind = .lsp, .capabilities = &[_]ProviderCapability{ .hover, .signature, .navigation, .code_action, .lint } };
+    const raw = [_][]const u8{
+        "lsp:hover:headline:docs",
+        "lsp:signature:call(arg):active=1",
+        "lsp:definition:src/main.zig:10:4",
+        "lsp:code_action:fix:remove unused",
+        "lint:warning:src/main.zig:1:1:style",
+    };
+    const rows = try providerRowsAlloc(std.testing.allocator, provider, &raw);
+    defer {
+        for (rows) |row| std.testing.allocator.free(row);
+        std.testing.allocator.free(rows);
+    }
+    for (rows, raw) |row, expected_payload| {
+        try std.testing.expectEqualStrings("zls", try providerIdFromRow(row));
+        try std.testing.expectEqualStrings(expected_payload, try providerPayloadFromRow(row));
+    }
+}