docs: map custom_instructions to --append-system-prompt (#1480)#1484
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docs: map custom_instructions to --append-system-prompt (#1480)#1484farmer-data wants to merge 1 commit into
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) The v1 migration guide mapped the v0 `custom_instructions` input to `claude_args: --system-prompt`, but these have different semantics: `custom_instructions` *appended* to Claude Code's default system prompt, while `--system-prompt` *replaces* it entirely. Users who followed the guide silently lost the whole built-in system prompt (tool-usage guidance, sub-agent conventions, etc.), keeping only their few custom lines. Fixes anthropics#1480: - Map `custom_instructions` -> `--append-system-prompt` (matches v0 append semantics) in the deprecated-inputs table, the migration example, and the checklist. - Correct the claude_args options table: `--system-prompt` replaces the entire prompt; add an `--append-system-prompt` row for append behavior. Docs-only; no code changes. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Summary
Fixes #1480. The v1 migration guide maps the v0
custom_instructionsinput toclaude_args: --system-prompt, but the semantics differ:custom_instructions(v0) appended to Claude Code's default system prompt.--system-promptreplaces the entire default system prompt.Anyone following the guide silently lost the whole built-in Claude Code system prompt (tool-usage guidance, sub-agent conventions, etc.), keeping only their custom lines. The append-semantics equivalent is
--append-system-prompt.Credit to @szihs for the report and the self-contained reproducer in #1480, which captures the composed
systemfield on the wire and shows--system-promptdropping the default prompt while--append-system-promptsupplements it.Changes (
docs/migration-guide.md, docs-only)custom_instructions→--append-system-promptin the deprecated-inputs table, the migration example, and the migration checklist.claude_argsoptions table:--system-promptreplaces the entire default system prompt; add an--append-system-promptrow for append behavior.Scope
Covers suggestions (1) and (2) from #1480. The optional runtime warning when
claude_argscontains--system-prompt— suggestion (3) — is a code change and is intentionally left as a separate follow-up.Verification
bun run format:check→ clean--append-system-promptthroughclaude_args.🤖 Generated with Claude Code