Add CLI Command

Add a new CLI command

The CLI is built with System.CommandLine. A subcommand is wired through three files in Cli/ plus a Core runner that holds the logic, and is then documented in README.md. Match the existing commands (export, batch-export, report, multi-report, validate, summary, upgrade) — don't invent a new shape.

Paths below are relative to the repo root (the directory containing MemorySnapshotDataTools.sln).

When to use

• Adding a brand-new subcommand (e.g. diff, prune, export-csv).
• Adding a new argument or --option to an existing subcommand.
• Exposing an existing Core capability through the CLI.

For SQL-touching logic inside the new command, also follow CLAUDE.md and docs/sql-safety.md — SQL safety is a first-class rule here.

The files you touch

Step by step

1. Cli/CliOptions.cs

• Add a value to the CommandKind enum.
• Add a property to CliOptions for each new argument/option. Reuse existing ones where they fit (Verbose, ReportDbPath, Destination, …) before adding new fields.

2. Cli/CommandLineBuilder.cs

Inside Build(...), following the existing blocks:

// ---- mycommand ----
var myCmd = new Command("mycommand", "One-line description shown in --help.");
var inputArg = new Argument<string>("input")
{
    Description = "Path to ...",
    Arity = ArgumentArity.ExactlyOne,
};
myCmd.Add(inputArg);

var someOpt = new Option<string>("--mode")
{
    Description = "...: a, b, or c.",
    DefaultValueFactory = _ => "a",
};
someOpt.AcceptOnlyFromAmong("a", "b", "c"); // validate enum-like options at parse time
myCmd.Add(someOpt);

myCmd.SetAction((ParseResult parseResult) =>
{
    var inputPath = ExpandPath(parseResult.GetValue(inputArg)!); // ALWAYS ExpandPath path args
    if (!File.Exists(inputPath))                                  // validate existence, return 1
    {
        Console.Error.WriteLine($"Input file not found: {inputPath}");
        return 1;
    }
    var options = new CliOptions
    {
        Command = CommandKind.MyCommand,
        // ... map parsed values onto CliOptions ...
    };
    return runMyCommand(options);
});

Then:

• Register it: root.Add(myCmd); near the bottom of Build.
• Add a Func<CliOptions, int> runMyCommand parameter to the Build(...) signature (the params are positional — keep the order consistent with Program.Main).

3. Cli/Program.cs

• Add a RunMyCommand(CliOptions options) static handler that delegates to your Core runner.
  • If the command reads an exported database, call SchemaGate.Check(path) first (see RunReport/RunSummary).
  • If it does cancellable work, use CreateCancellationSource() and catch OperationCanceledException → return 2 (see RunExport).
• Add RunMyCommand to the CommandLineBuilder.Build(...) call in Main in the matching position.

4. Core runner (the logic)

Put real work in Core/..., not in Cli/. Mirror an existing runner (SummaryReportRunner, ExportRunner): a XxxRunOptions record + a static int Run(...) that returns an exit code and reports via IProgressReporter. If it builds SQL, parameterize values and validate identifiers per docs/sql-safety.md; open the DB read-only if it only reads (Mode=ReadOnly / ACCESS_MODE=READ_ONLY).

5. Tests

Add tests under Tests/ targeting the Core runner / calculator (e.g. BatchExportRunnerTests.cs, SummaryMetricsCalculatorTests.cs). Helpers you assert on must be public — InternalsVisibleTo is a no-op here, so Core internals are not visible to Tests.

6. Document in README.md

This step is required — a new command is not done until the README documents it. In README.md:

• Add a ### <verb the command does> subsection under How to use, after the existing command subsections, with the invocation form and a worked example, matching the style of the export and report sections:

  ### <What the command does>
  
  ```bash
  dotnet run --project Cli/MemorySnapshotDataTools.Cli.csproj -- mycommand <args> [options]
  ```
  
  - **`--option`:** what it does (default: …).
  
  **Example:**
  
  ```bash
  dotnet run --project Cli/MemorySnapshotDataTools.Cli.csproj -- mycommand ./in.duckdb --mode b
  ```
  

• If the command changes the headline behavior, add a bullet to the What it does list at the top, and update Output/Schema if it writes new tables/files.

• Consider also updating, when relevant: the Direct CLI invocation list in run-memory-snapshot-data-tool/SKILL.md, and docs/intro.md / docs/runbook.md.

7. Build, test, and verify it runs

dotnet build MemorySnapshotDataTools.sln
dotnet test MemorySnapshotDataTools.sln
dotnet run --project Cli/MemorySnapshotDataTools.Cli.csproj -- --help          # command listed?
dotnet run --project Cli/MemorySnapshotDataTools.Cli.csproj -- mycommand --help # args/options correct?

To exercise the full pipeline (build → run → screenshot), use the run-memory-snapshot-data-tool skill's driver.

Conventions & gotchas

• Always ExpandPath(...) path arguments/options before use — it expands ~, env vars, and resolves to a full path. Every existing handler does this.
• Validate inputs in SetAction and return 1 for bad args / missing files, before constructing CliOptions.
• Exit codes are meaningful and asserted on: 0 success, 1 bad args / file not found, 2 cancelled (Ctrl-C), 3 validation/error. Keep yours consistent.
• Enum-like string options → option.AcceptOnlyFromAmong("a","b","c") so bad values are rejected at parse time (see --validate, --destination).
• Build's handlers are positional Func<CliOptions,int> parameters. Add yours in the same position in both the Build signature and the Main call site, or the wrong handler runs.
• Reading an exported DB? Call SchemaGate.Check(path) first so a stale/newer schema fails with a clear message instead of a confusing query error.
• SQL safety is non-negotiable — never interpolate external values into SQL; bind parameters and validate identifiers (CLAUDE.md, docs/sql-safety.md).

Checklist

• CommandKind value + CliOptions properties added (Cli/CliOptions.cs).
• Command, args/options, SetAction, root.Add, and new Build param added (Cli/CommandLineBuilder.cs).
• RunXxx handler added and threaded through Main (Cli/Program.cs).
• Logic lives in a Core XxxRunner (+ XxxRunOptions); SQL is parameterized / read-only.
• Tests added for the Core logic (public helpers).
• README.md documents the command (usage + example), other docs/skill updated if relevant.
• dotnet build + dotnet test pass; -- --help and -- mycommand --help look right.