Add Git attribution and profile email selection - #14924

Prototype overview and documentation

DO NOT MERGE. This stack is almost entirely vibe coded. These drafts are for handy review and prototyping, not merging as-is.

Expect the code to be really bad in places: highly coupled, handling edge cases that do not really matter, or doing suspiciously fragile things like parsing GraphQL request bodies.

I suspect some of the suspicious code also exposes the complexity of this feature set, because account selection, Git configuration, scope precedence, worktrees, SSH and API requests all interact.

The prototype experience is the purpose, not the code. I want to find out whether the experience is useful, not defend this implementation or treat it as a design to preserve.

Description

Follow on from #14923

Choosing the authentication account does not choose the name and email used on Git commits. This PR adds optional Git attribution to identities and explicit @public and @noreply email lookup.

Layer 5 of an eight-part prototype review stack. This is a way to review the design and implementation in smaller pieces, not a proposal to merge the current stack as-is.

How did you test this change?

I inspected the identity file containing Git attribution, made local commits in the main checkout and a linked worktree, and checked shared edits. I also exercised real profile lookups, fixed-address snapshots and a failed public-email lookup that preserved the previous value.

$ cat ~/.config/gh/identities/personal.gitconfig
...
[user]
	name = "William Martin"
	email = "william@example.invalid"
[credential "https://github.com"]
	username = "williammartin"

A real noreply profile lookup is a fixed snapshot

Literal attribution follows the repository family

Missing public email does not overwrite an identity

Key points

The included identity file supplies ordinary user.name and user.email defaults. Authentication remains separate, and Git can still apply stronger local or environment settings. These defaults do not independently distinguish author and committer.

Profile selectors resolve once and store a concrete address. Changing unrelated identity settings does not silently refresh it. The literal email addresses in local commit demonstrations are examples, not claims about an account profile.

Notes for reviewers

The profile-snapshot recording changes the identity account to demonstrate the current snapshot behaviour. I am not sure account edits should be supported at all. That unresolved design question is called out in the identity foundation PR, not endorsed by this recording.

The recordings use the product code at this layer, not a later stack endpoint. The included offline replay scripts are supplementary and do not reproduce the live-account recordings.

make
env -i HOME="$HOME" PATH=/usr/bin:/bin:/opt/homebrew/bin \
  /bin/bash script/multiaccount-review/05-attribution.sh --gh "$PWD/bin/gh"

Authorship and follow-up

Who wrote this:

• A human wrote it.
• An agent wrote it under close human direction.
• An agent wrote it independently, and no human has guided the implementation beyond the initial prompt.

Who answers review comments:

• @username will read and reply directly. Name the account.
• An agent will draft replies and @username will read them before they are posted.
• Nobody has explicitly committed to replying.

Acceptance Criteria

Prototype behaviour under review:

Given an identity has optional Git attribution.

When Git loads that identity through a matching binding.

Then the included defaults apply unless ordinary Git precedence selects a stronger value.

DO NOT MERGE