agent: reduce allocations and reuse buffers

src/agent/Agent.zig

@@ -443,18 +443,17 @@ fn runScript(self: *Self, path: []const u8) bool {
     };
     defer file.close();
 
-    const content = file.readToEndAlloc(self.allocator, 10 * 1024 * 1024) catch |err| {
-        self.terminal.printErrorFmt("Failed to read script: {s}", .{@errorName(err)});
-        return false;
-    };
-    defer self.allocator.free(content);
-
     self.terminal.printInfoFmt("Running script: {s}", .{path});
 
     var script_arena: std.heap.ArenaAllocator = .init(self.allocator);
     defer script_arena.deinit();
     const sa = script_arena.allocator();
 
+    const content = file.readToEndAlloc(sa, 10 * 1024 * 1024) catch |err| {
+        self.terminal.printErrorFmt("Failed to read script: {s}", .{@errorName(err)});
+        return false;
+    };
+
     var iter: Command.ScriptIterator = .init(sa, content);
     var last_comment: ?[]const u8 = null;
     var replacements: std.ArrayList(Replacement) = .empty;
@@ -1021,8 +1020,8 @@ fn buildUserMessageParts(
     }
 
     var parts: std.ArrayList(zenai.provider.ContentPart) = .empty;
-    const combined = try std.fmt.allocPrint(ma, "{s}{s}", .{ text_prefix.items, user_input });
-    try parts.append(ma, .{ .text = combined });
+    try text_prefix.appendSlice(ma, user_input);
+    try parts.append(ma, .{ .text = try text_prefix.toOwnedSlice(ma) });
     for (inline_parts.items) |p| try parts.append(ma, p);
     return parts.toOwnedSlice(ma);
 }

src/agent/Recorder.zig

@@ -8,6 +8,9 @@ const Self = @This();
 allocator: std.mem.Allocator,
 file: ?std.fs.File,
 needs_separator: bool,
+/// Reused between `record()` calls so each command line doesn't alloc/free.
+/// Cleared with `clearRetainingCapacity` instead.
+buf: std.Io.Writer.Allocating,
 
 /// Append-open `path`, inserting a leading newline if the file is non-empty.
 /// A null path disables recording.
@@ -27,10 +30,11 @@ pub fn init(allocator: std.mem.Allocator, path: ?[]const u8) Self {
         break :blk f;
     } else null;
 
-    return .{ .allocator = allocator, .file = file, .needs_separator = false };
+    return .{ .allocator = allocator, .file = file, .needs_separator = false, .buf = .init(allocator) };
 }
 
 pub fn deinit(self: *Self) void {
+    self.buf.deinit();
     if (self.file) |f| f.close();
 }
 
@@ -38,11 +42,10 @@ pub fn record(self: *Self, cmd: Command.Command) void {
     const f = self.file orelse return;
     if (!cmd.isRecorded()) return;
 
-    var aw: std.Io.Writer.Allocating = .init(self.allocator);
-    defer aw.deinit();
-    cmd.format(&aw.writer) catch return;
-    aw.writer.writeByte('\n') catch return;
-    _ = f.write(aw.written()) catch return;
+    self.buf.clearRetainingCapacity();
+    cmd.format(&self.buf.writer) catch return;
+    self.buf.writer.writeByte('\n') catch return;
+    _ = f.write(self.buf.written()) catch return;
     self.needs_separator = true;
 }
 
@@ -61,7 +64,7 @@ test "record writes state-mutating commands" {
 
     const file = tmp.dir.createFile("test.lp", .{ .read = true }) catch unreachable;
 
-    var recorder: Self = .{ .allocator = std.testing.allocator, .file = file, .needs_separator = false };
+    var recorder: Self = .{ .allocator = std.testing.allocator, .file = file, .needs_separator = false, .buf = .init(std.testing.allocator) };
     defer recorder.deinit();
 
     recorder.record(Command.parse("GOTO https://example.com"));
@@ -103,7 +106,7 @@ test "record skips empty and comment lines" {
 
     const file = tmp.dir.createFile("test2.lp", .{ .read = true }) catch unreachable;
 
-    var recorder: Self = .{ .allocator = std.testing.allocator, .file = file, .needs_separator = false };
+    var recorder: Self = .{ .allocator = std.testing.allocator, .file = file, .needs_separator = false, .buf = .init(std.testing.allocator) };
     defer recorder.deinit();
 
     recorder.record(Command.parse(""));
@@ -120,7 +123,7 @@ test "record skips empty and comment lines" {
 }
 
 test "recorder with null file is no-op" {
-    var recorder: Self = .{ .allocator = std.testing.allocator, .file = null, .needs_separator = false };
+    var recorder: Self = .{ .allocator = std.testing.allocator, .file = null, .needs_separator = false, .buf = .init(std.testing.allocator) };
     recorder.record(Command.parse("GOTO https://example.com"));
     recorder.recordComment("# test");
     recorder.deinit();

src/browser/tools.zig

@@ -1011,9 +1011,11 @@ pub fn substituteEnvVars(arena: std.mem.Allocator, input: []const u8) []const u8
                 // Same gate as `execGetEnv`: only `LP_*` is resolvable. A
                 // prompt-injected `fill('$ANTHROPIC_API_KEY')` would otherwise
                 // leak the resolved value into the page DOM.
-                const env_val: ?[:0]const u8 = if (std.ascii.startsWithIgnoreCase(name, "LP_")) blk: {
-                    const name_z = arena.dupeZ(u8, name) catch return input;
-                    break :blk std.posix.getenv(name_z);
+                var name_buf: [256]u8 = undefined;
+                const env_val: ?[:0]const u8 = if (std.ascii.startsWithIgnoreCase(name, "LP_") and name.len < name_buf.len) blk: {
+                    @memcpy(name_buf[0..name.len], name);
+                    name_buf[name.len] = 0;
+                    break :blk std.posix.getenv(name_buf[0..name.len :0]);
                 } else null;
                 if (env_val) |val| {
                     result.appendSlice(arena, val) catch return input;