fix(cli): reject a standalone assertion with no arguments

[Chemaclass]

🤔 Background

Related #877

exec_assert computed last_index as args_count - 1 without checking the count.
With no arguments that is -1, and Bash 3.x has no negative array subscripts, so the
expansion failed with a raw bad array subscript — and the run still exited 0.

docs/standalone.md presents this subcommand for integration and end-to-end checks, so
a mistyped invocation in a deploy script reported success.

💡 Changes

• Reject an assertion invoked with no arguments, naming it in the message, and exit non-zero
• Removes a Bash 3.0 compatibility violation (negative array subscript) flagged by .claude/rules/bash-style.md
• Add acceptance coverage for both crash shapes plus a guard that a single-argument assertion (assert empty "") still succeeds

[Chemaclass]

🤔 Background

Related #877

exec_assert computed last_index as args_count - 1 without checking the count.
With no arguments that is -1, and Bash 3.x has no negative array subscripts, so the
expansion failed with a raw bad array subscript — and the run still exited 0.

docs/standalone.md presents this subcommand for integration and end-to-end checks, so
a mistyped invocation in a deploy script reported success.

💡 Changes

• Reject an assertion invoked with no arguments, naming it in the message, and exit non-zero
• Removes a Bash 3.0 compatibility violation (negative array subscript) flagged by .claude/rules/bash-style.md
• Add acceptance coverage for both crash shapes plus a guard that a single-argument assertion (assert empty "") still succeeds

[Chemaclass]

🤔 Background

Related #877

exec_assert computed last_index as args_count - 1 without checking the count.
With no arguments that is -1, and Bash 3.x has no negative array subscripts, so the
expansion failed with a raw bad array subscript — and the run still exited 0.

docs/standalone.md presents this subcommand for integration and end-to-end checks, so
a mistyped invocation in a deploy script reported success.

💡 Changes

• Reject an assertion invoked with no arguments, naming it in the message, and exit non-zero
• Removes a Bash 3.0 compatibility violation (negative array subscript) flagged by .claude/rules/bash-style.md
• Add acceptance coverage for both crash shapes plus a guard that a single-argument assertion (assert empty "") still succeeds

[Chemaclass]

🤔 Background

Related #877

exec_assert computed last_index as args_count - 1 without checking the count.
With no arguments that is -1, and Bash 3.x has no negative array subscripts, so the
expansion failed with a raw bad array subscript — and the run still exited 0.

docs/standalone.md presents this subcommand for integration and end-to-end checks, so
a mistyped invocation in a deploy script reported success.

💡 Changes

• Reject an assertion invoked with no arguments, naming it in the message, and exit non-zero
• Removes a Bash 3.0 compatibility violation (negative array subscript) flagged by .claude/rules/bash-style.md
• Add acceptance coverage for both crash shapes plus a guard that a single-argument assertion (assert empty "") still succeeds

[Chemaclass]

🤔 Background

Related #877

exec_assert computed last_index as args_count - 1 without checking the count.
With no arguments that is -1, and Bash 3.x has no negative array subscripts, so the
expansion failed with a raw bad array subscript — and the run still exited 0.

docs/standalone.md presents this subcommand for integration and end-to-end checks, so
a mistyped invocation in a deploy script reported success.

💡 Changes

• Reject an assertion invoked with no arguments, naming it in the message, and exit non-zero
• Removes a Bash 3.0 compatibility violation (negative array subscript) flagged by .claude/rules/bash-style.md
• Add acceptance coverage for both crash shapes plus a guard that a single-argument assertion (assert empty "") still succeeds

[Chemaclass]

🤔 Background

Related #877

exec_assert computed last_index as args_count - 1 without checking the count.
With no arguments that is -1, and Bash 3.x has no negative array subscripts, so the
expansion failed with a raw bad array subscript — and the run still exited 0.

docs/standalone.md presents this subcommand for integration and end-to-end checks, so
a mistyped invocation in a deploy script reported success.

💡 Changes

• Reject an assertion invoked with no arguments, naming it in the message, and exit non-zero
• Removes a Bash 3.0 compatibility violation (negative array subscript) flagged by .claude/rules/bash-style.md
• Add acceptance coverage for both crash shapes plus a guard that a single-argument assertion (assert empty "") still succeeds

[Chemaclass]

🤔 Background

Related #877

exec_assert computed last_index as args_count - 1 without checking the count.
With no arguments that is -1, and Bash 3.x has no negative array subscripts, so the
expansion failed with a raw bad array subscript — and the run still exited 0.

docs/standalone.md presents this subcommand for integration and end-to-end checks, so
a mistyped invocation in a deploy script reported success.

💡 Changes

• Reject an assertion invoked with no arguments, naming it in the message, and exit non-zero
• Removes a Bash 3.0 compatibility violation (negative array subscript) flagged by .claude/rules/bash-style.md
• Add acceptance coverage for both crash shapes plus a guard that a single-argument assertion (assert empty "") still succeeds

[Chemaclass]

🤔 Background

Related #877

exec_assert computed last_index as args_count - 1 without checking the count.
With no arguments that is -1, and Bash 3.x has no negative array subscripts, so the
expansion failed with a raw bad array subscript — and the run still exited 0.

docs/standalone.md presents this subcommand for integration and end-to-end checks, so
a mistyped invocation in a deploy script reported success.

💡 Changes

• Reject an assertion invoked with no arguments, naming it in the message, and exit non-zero
• Removes a Bash 3.0 compatibility violation (negative array subscript) flagged by .claude/rules/bash-style.md
• Add acceptance coverage for both crash shapes plus a guard that a single-argument assertion (assert empty "") still succeeds