feat(alias): forward positional args to templates via {{ args }}

[max-sixty]

Summary

Non-flag tokens after an alias name are forwarded to the template as {{ args }} — a space-joined, shell-escaped sequence. wt s some-branch with s = "wt switch {{ args }}" expands to wt switch some-branch.

Before: wt s some-branch errored with Unexpected argument 'some-branch' for alias 's'.

Why

Users want to pass arguments through to aliased commands — wt s foo → wt switch foo — without configuring --var foo=… for every possible parameter. Positional args are the natural fit.

Behavior

{{ args }} is a minijinja sequence. All four access patterns work:

Template	Render
{{ args }}	space-joined, per-element shell-escaped
{{ args[0] }}	first arg (escaped)
{{ args | length }}	count
{% for a in args %}	iteration

Each element is individually shell-escaped, so wt run 'a b' 'c;d' splices in as 'a b' 'c;d' and can't inject shell syntax. Positionals interleave freely with flags — wt deploy foo --dry-run bar collects ["foo", "bar"] into args.

--dry-run, --yes, -y, --var KEY=VALUE, and --KEY=VALUE parsing are unchanged.

Navigating the diff

• src/config/expansion.rs — new ShellArgs struct wraps Vec<String> and implements minijinja's Object trait with ObjectRepr::Seq. Its render() writes shell_escape::unix::escape of each element, space-joined. The shell-escape formatter in setup_template_env detects ShellArgs via downcast_object_ref and passes its Display through unmodified — so bare {{ args }} isn't double-escaped by the generic per-value escape. Iteration and indexing yield plain Value::from(String) that still flow through the generic formatter. New ALIAS_ARGS_KEY constant ("args") is the reserved context key carrying the JSON-encoded list.
• src/commands/alias.rs — AliasOptions gains a positional_args: Vec<String> field. AliasOptions::parse collects non-flag tokens into it instead of erroring. run_alias inserts the JSON-encoded list into context_map under ALIAS_ARGS_KEY right after build_hook_context. The sole special-case lives in expand_template, which rehydrates the key as a ShellArgs object; all other call sites (hooks, for-each, eval) are untouched and never see the key.
• validate_template — injects an empty ShellArgs so templates referencing {{ args }} pass pre-flight validation. args is added to TEMPLATE_VARS.
• docs/content/extending.md — new "Forwarding positional arguments" subsection under Aliases with a shell-safety guarantee and access-pattern examples.

Tests

3233 tests pass, lints clean. New:

• src/commands/alias.rs — test_parse snapshots extended with positional cases including interleaved flags and metacharacter-laden args. test_parse_errors no longer expects "Unexpected argument".
• src/config/expansion.rs — test_expand_template_args_sequence covers indexing, iteration, and length. test_expand_template_args_empty confirms empty renders to empty string. test_expand_template_args_shell_metachar_safety asserts the exact output for ['; rm -rf /', '$(whoami)', "a'b"]. test_validate_template_valid now covers {{ args }}, {{ args | length }}, and iteration.
• tests/integration_tests/step_alias.rs — end-to-end snapshots for wt step <alias> positionals, wt <alias> some-branch --dry-run, empty positionals, and sequence-style access.

Do-nots

• No changes to --dry-run, --yes, --var, or --KEY=VALUE parsing — the broader flag-handling question (whether alias-level flags should move pre-name) is being designed separately.
• No KEY=value bare-token parsing for vars — deferred.
• No change to wt step <alias> semantics beyond inheriting positional support via shared AliasOptions::parse.

This was written by Claude Code on behalf of Maximilian

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