Custom prompts: passing arguments ($1..$9, $ARGUMENTS) + @ file picker + frontmatter hints

[evandavid1]

Key features

• Custom prompts accept arguments: $1..$9, $ARGUMENTS, and $$ (literal)
• @ file picker in composer: type @ to fuzzy‑search and insert quoted paths
• Frontmatter hints: optional description + argument-hint shown in palette (body stripped before send)

Why

• Make saved prompts reusable with runtime parameters.
• Improve discoverability with concise, helpful hints in the slash popup.
• Preserve privacy and approvals; no auto‑execution added.

Details

• Protocol: extend CustomPrompt with description, argument_hint (optional).
• Core: parse minimal YAML‑style frontmatter at file top; strip it from the submitted body.
• TUI: expand arguments; insert @ paths; render description/argument-hint or fallback excerpt.
• Docs: prompts.md updated with frontmatter and argument examples.

Tests

• Frontmatter parsing (description/argument-hint extracted; body stripped).
• Popup rows show description + argument-hint; excerpt fallback; builtin name collision.
• Argument expansion for $1..$9, $ARGUMENTS, $$; quoted args and @ path insertion.

Safety / Approvals

• No changes to approvals or sandboxing; prompts do not auto‑run tools.

Related

• Closes Custom prompts - passing arguments #2890
• Related /Custom-Prompts NOT support argument (e.g "@" etc) input #3265
• Complements Saved prompts: transcript redaction + per-submission custom instructions #3403

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[evandavid1]

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[evandavid1]

Converting to draft to align with the Contributing guide (feature proposals should be discussed/approved before review). This PR implements a narrowly scoped, backward‑compatible change set and addresses existing enhancement requests (#2890) and related reports (#3265). I’m happy to adjust scope or split this further per maintainer guidance. Requesting a maintainer’s thumbs‑up on the approach (arguments .., , 44259; @ file picker inserts paths; optional frontmatter hints surfaced in the palette; no tool auto‑exec; tests + docs included).

[evandavid1]

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[dedrisian-oai]

Hey @evandavid1, looks great and thanks a ton for your contribution! 🙌

In the interest of being very quick ⚡️ I'm going to merge this into a new branch (feat/custom-prompts-frontmatter) and make some modifications to combine it with named args. Will hopefully be merged into main soon.