implement the includeCoAuthoredBy option

[CodinCat]

let me know if you want to merge this. I'll resolve the conflicts and feel free to just close this PR if you don't want this to be added.

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fix #919

Add the include_co_authored_by option. The behavior is copied from Claude Code.

When it's true (default) the prompt remains unchanged. I copied the original prompt and verified it with a temporary test:

test("bash.txt", () => {
  const bashTxtPath = join(process.cwd(), "packages/opencode/src/tool/bash-backup.txt")
  const currentContent = readFileSync(bashTxtPath, "utf-8")
  expect(replaceCoAuthoredMessage()).toBe(currentContent)
})

And this is how the three places look when it's false. This should be the same as Claude Code:

1

2

3

---

actual usage:

true:

false:

[samholmes]

Can confirm this works nicely, thanks!

An alternative implementation which leverages no custom templating system and instead opts in for using mustache: https://github.com/sst/opencode/pull/1430