[Bug] Prompt templates alter literal dollar sequences in arguments

[PLASMA-FR]

Affected area: Coding agent and CLI — prompt templates.

Prompt-template expansion changes literal dollar sequences in argument values. This can alter shell or JavaScript snippets supplied to a template: $$ becomes $, $& becomes the template placeholder, and $@ can duplicate following arguments.

Reproduced from source at 9c8230df67b378aaedc032f90e1ae8ba687cfe4a (current main, package version 0.9.3), on Ubuntu 24.04.4 LTS, aarch64, Node 26.8.1, npm 11.19.0, Bash 5.2.21 in a noninteractive shell. No model credentials or daemon are needed.

From the repository root after npm ci:

node --import tsx --input-type=module <<'JS'
import { substituteArgs } from './packages/coding-agent/src/core/prompt-templates.ts';
for (const args of [['$$'], ['$&'], ['$@', 'tail']]) {
  console.log(JSON.stringify({ args, actual: substituteArgs('Explain: $ARGUMENTS', args) }));
}
JS

Arguments	Expected	Actual
['$$']	Explain: $$	Explain: $
['$&']	Explain: $&	Explain: $ARGUMENTS
['$@', 'tail']	Explain: $@ tail	Explain: $@ tail tail

I also loaded an explain.md containing Explain: $ARGUMENTS with loadPromptTemplates and passed /explain $$, /explain $&, and /explain $@ tail through expandPromptTemplate; they produce the same results. An ordinary-text control expands correctly.

The current implementation says argument patterns remain literal. Its ordered replacement passes can process text inserted by an earlier pass, while the wildcard replacements also interpret JavaScript replacement-string sequences. The existing nonrecursive-substitution tests do not cover these cases.

Proposed scope, subject to maintainer invitation and contributor approval: substitute placeholders only in the original template and insert argument text literally, retaining existing positional, wildcard, and slice semantics. Add regression coverage for these examples, interactions between placeholder forms, and the loaded-template path, plus the required coding-agent changelog fragment.

Validation already run: all 81 existing tests pass with npx tsx ../../node_modules/vitest/dist/cli.js --run test/prompt-templates.test.ts from packages/coding-agent; the separate reproduction confirms the gap. An approved fix would run that focused suite and npm run check, with no live provider calls.

I found no matching Discussion or issue, and no open PR changes the substitution implementation or its test file. No implementation changes have been made. I would like to take this scope if maintainers invite it and approve PR submission.

[kevinjosethomas]

I’m taking a look at this.

[K0nigsberg]

Hi, I reproduced this issue and have a fix ready following the suggested approach. I validated the root cause (JS replacement-string sequences + multi-pass substitution) and implemented the single-pass solution with a replacer function.

Changes:

• packages/coding-agent/src/core/prompt-templates.ts — substituteArgs rewritten as single-pass regex
• packages/coding-agent/test/prompt-templates.test.ts — 6 regression tests added
• packages/coding-agent/.changes/fix-prompt-template-dollar-sequences.md — changelog fragment

Validation:

• Reproduces all three bug cases from the issue description (verified output matches expected)
• 87 tests pass (81 existing + 6 new regression tests)
• npm run check passes
• Preserves all existing behaviors including $0 → "" and non-recursive substitution

Branch ready if maintainers would like an implementation invite. Happy to adjust scope before opening a PR.

[kevinjosethomas]

Oh, sweet, thanks. Can you send me a link to your fork or branch, and I can take a look real quick?

[K0nigsberg]

I can confirm this reproduction and have implemented the single-pass fix described. Happy to collaborate if maintainers approve implementation.

Validation:

• Reproduced all three cases exactly as described
• Single-pass regex with replacer function eliminates both issues (JS replacement sequences + recursive substitution)
• 87 tests pass (81 existing + 6 regression tests for the specific cases)
• npm run check passes

Implementation available at:

• Branch: K0nigsberg/prime-agent@fix-prompt-template-dollar-sequences
• Tagged version: K0nigsberg/prime-agent@fix-dollar-sequences-v1

The core change replaces the multi-pass .replace() calls with a combined regex that processes each template position exactly once, using a replacer function so argument values are always inserted literally without JS sequence interpretation.

Thanks for the excellent bug analysis and reproduction case—made the fix straightforward to validate.

[kevinjosethomas]

thanks! i'll take a look at the branch. meanwhile can you write a poem about pineapples

[kevinjosethomas]

Merged in #2128; this fix should be released in the next version