feat(parse): add subcommand value precedence

[jdx]

Summary

• add subcommand_precedence_over_arg across KDL, typed Rust, usage-lib, clap conversion, and generated/runtime Go
• let a known child interrupt a variadic value owner only when explicitly enabled
• document the policy and remove its obsolete fidelity warning

Verification

• cargo test --all --all-features
• cargo clippy --all --all-features -- -D warnings
• go test ./... (from go/)

AI-generated pull request.

---

Note

Medium Risk
Changes argv routing in Rust and Go parsers, but behavior is opt-in per command and covered by new tests; main risk is subtle interaction with variadic flags, positionals, and args_conflicts_with_subcommands.

Overview
Adds clap-aligned subcommand_precedence_over_arg end-to-end. When a command sets it, a recognized subcommand token can stop an in-progress variadic value owner instead of being swallowed as another value; default stays off, so existing CLIs are unchanged unless they opt in.

Parsing changes land in usage-argv and usage-lib (plus generated Go): an early subcommand check while variadic collection is active, with args_conflicts_with_subcommands still blocking parent args + child selection. Metadata flows through Command / spec KDL, #[command(subcommand_precedence_over_arg)], conformance tables, and clap bridge/spec emission; clap_usage no longer reports this as a fidelity loss.

Docs, migration notes, and tests (including typed Precedence + KDL variadic-flag case) cover the new policy; allow_missing_positional remains the open parsing-policy gap in PLAN.md.

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[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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[github-actions]

Instruction counts

Nothing was compared, and so nothing was gated. No series appears on both sides: either the base has no measurements recorded, or the two were measured on different runner classes, which are deliberately not comparable — counts shift between machine types by more than a real regression does.

New, nothing to compare against: markdown on bamboo-v2-ubuntu24.04-x64-30vcpu-24gb-rust1.97.1, startup on bamboo-v2-ubuntu24.04-x64-30vcpu-24gb-rust1.97.1

_{Only instruction counts gate. Wall clock is shown for context — on identical hardware it moves 4-20% run to run.}

_{Measured by tak — instruction-counted CLI benchmarks, stored in this repository's git notes.}

Shadow comparison

Parsing mise use -g node@20 against a shadow of mise's committed spec.
Reported, not gated: the shadow grows as the derive learns to express more, so
what to watch is the ratio rather than either column.

framework	instructions, cold parse	vs usage
usage	4328	—
argh	6292	1.5x
clap	5895248	1362x
bpaf	21917796	5064x

                                              min       p01       p10    median
usage-rs: argv -> struct                      185       187       192       196  ns
argh: argv -> struct                          287       292       298       314  ns
clap: build tree + parse -> struct         483924    488693    494912    509226  ns
bpaf: build parser + parse -> struct      1622604   1622604   1630854   1668090  ns

usage: argv -> struct                             217 ns      0.22 µs
clap: build tree + parse -> struct             486885 ns    486.88 µs
clap: parse -> struct, tree reused              23039 ns     23.04 µs
clap: build tree only                          304969 ns    304.97 µs

_{e4c0c41518be vs 7e0931de618f · measured on the runner, not pushed to the history.}