fix(cli): 2D-parallelism error tells the user to pass --tensor-parallel-size, which does not exist #1112

Summary

The 2D (pipeline × tensor) parallelism validation in src/commands/generate.rs:367-371 fails with a message telling the user to pass --tensor-parallel-size > 1. That flag does not exist; the real flag is --tp-size. A user who follows the instruction gets error: unexpected argument '--tensor-parallel-size' found. A comment three lines above points at two docs/en/distributed/*.md files that also do not exist.

Background

src/commands/generate.rs:367-371:

ensure!(
    pp.pp_size >= 2 || pp.pp_layers.is_some(),
    "2D parallelism requires --pp-size >= 2 (or an explicit --pp-layers spec) \
     alongside --tensor-parallel-size > 1"
);

grep -rn "tensor-parallel-size" src/ returns exactly one hit: this message string. It is never a clap flag. The tensor-parallel rank count is --tp-size, defined at src/main.rs:728, src/main.rs:1378, and src/bin/mlx_server.rs:763. The message is otherwise accurate (--pp-size and --pp-layers are both real), which makes the one wrong name more misleading than a vague message, because the other two names check out.

The comment at src/commands/generate.rs:362-364 points at docs/en/distributed/pipeline-parallelism.md and docs/en/distributed/tensor-parallelism.md. Neither exists; docs/en/ has never been part of this repository, and these are the only two docs/en/ references in src/. The real operator document is docs/distributed.md.

Proposed Solution

1. Change --tensor-parallel-size to --tp-size in the ensure! message.
2. Repoint the two comment references at docs/distributed.md, or drop them if that document does not cover 2D composition.

Implementation Notes

• Message and comment text only; the validation logic is unchanged.
• Worth a quick sweep of the neighbouring ensure! messages in the same function while there: --pp-micro-batch-size (src/commands/generate.rs:356), --pp-size, and --pp-layers all resolve, but the file is the kind of place where one wrong name suggests checking the rest.

Acceptance Criteria

• Every flag named in the message is one the binary accepts.
• No docs/en/ reference remains in src/.
• grep -rn -- "--tensor-parallel-size" src/ returns nothing.
• Message text only; the validation logic is unchanged.

Original Suggestion

Title: fix(cli): a 2D-parallelism error tells the user to pass --tensor-parallel-size, which does not exist

Problem / Background

src/commands/generate.rs:367-371 validates a 2D (pipeline × tensor) parallel topology and
fails with:

ensure!(
    pp.pp_size >= 2 || pp.pp_layers.is_some(),
    "2D parallelism requires --pp-size >= 2 (or an explicit --pp-layers spec) \
     alongside --tensor-parallel-size > 1"
);

There is no --tensor-parallel-size flag. The tensor-parallel rank count is --tp-size,
defined at src/main.rs:728, src/main.rs:1378, and src/bin/mlx_server.rs:763, with no
--tensor-parallel-size alias anywhere in the tree.

A user who hits this error and follows its instruction gets
error: unexpected argument '--tensor-parallel-size' found. The message is otherwise
accurate and actionable — --pp-size and --pp-layers are both real — which makes the one
wrong name more misleading than a vague message would be, because the other two names in the
same sentence check out.

Second defect in the same block

The comment three lines above, src/commands/generate.rs:362-364, points at the operator
guide:

// 2D (PP x TP) composition is now supported. See
// `docs/en/distributed/pipeline-parallelism.md` and
// `docs/en/distributed/tensor-parallelism.md` for the operator guide.

Neither file exists. docs/en/ has never been part of this repository
(git log --all -- docs/en is empty). These are the only two docs/en/ references in
src/, so fixing them here clears the pattern from the code entirely. The real
operator-facing document is docs/distributed.md.

Proposed solution

1. Change --tensor-parallel-size to --tp-size in the ensure! message.
2. Repoint the two comment references at docs/distributed.md, or drop them if that
   document does not cover 2D composition.

Acceptance criteria

• Every flag named in the message is one the binary accepts.
• No docs/en/ reference remains in src/.
• grep -rn -- "--tensor-parallel-size" src/ returns nothing.
• Message text only; the validation logic is unchanged.

Technical considerations

Worth a quick sweep of the neighbouring ensure! messages in the same function while you
are there — --pp-micro-batch-size (src/commands/generate.rs:356), --pp-size and
--pp-layers all resolve, but the file is the kind of place where one wrong name suggests
checking the rest.