[bug] teamai push --branch: team-config edits attach to an existing PR group instead of the new branch #800

Summary

teamai push --branch <name> was added in #690 (merged as 9d3a91c). A latent
grouping bug ships with it: when uncommitted teamai.yaml edits are pushed
alongside both an existing open-PR group and a new --branch group, the
config rides on the first group — which is always the reused existing PR —
so the explicit --branch never receives the config, and an unrelated review
gets modified.

Flagged as a P1 in the #690 review and merged as a known issue; filing it for
follow-up.

Root cause

In pushCore() the config rides on the first group and is then cleared:

// src/push.ts:1502
let configRider = pendingTeamConfig !== null;
...
for (const group of groups) {
  const outcome = await pushGroup({
    ...
    includeTeamConfig: configRider,   // src/push.ts:1513
    branch: options.branch,           // src/push.ts:1514
  });
  ...
  configRider = false;                // src/push.ts:1529 — only the first group gets it
}

But planPushGroups() (src/utils/pending-push.ts) always orders reused
(existing-PR) groups first and collapses all new resources into the single
trailing group:

// reused entries pushed first…
for (const entry of newestFirst) { ...; groups.push({ items, reuse: entry }); }
// …new resources appended last as one group
const rest = selected.filter((i) => !claimed.has(...));
if (rest.length > 0) groups.push({ items: rest });

So configRider is consumed by the reused group, and --branch (which only
sets branchName for the new group) never carries the config.

Impact

When triggered:

• the --branch destination does not get the teamai.yaml change (the
  feature silently no-ops for config); and
• an unrelated existing open PR is amended with the user's config edit, with no
  warning — it can be merged into the default branch as part of that PR and
  pollute the team-wide teamai.yaml.

The amendment is silent, so it is easy to miss until it has already spread.

Reproduction

1. Have an uncommitted teamai.yaml edit in the team-repo clone
   (e.g. after teamai source add, which writes but does not commit).
2. Have at least one unmerged open PR whose resources are selected again this
   run (forms a reuse group).
3. Run teamai push --branch <name> with a new resource in the same run.

Observed: the config lands on the existing PR's branch, not <name>; <name>
carries only the new resource.

Suggested fix

When options.branch is set, route configRider to the new group rather
than the first (reused) group — or reject the ambiguous combination
(edited teamai.yaml + existing-PR group + --branch) with a clear error,
mirroring the existing multi-new-group guard at src/push.ts:1478.

Related

Follow-up to #690 (fixes #663). Known P1 merged deliberately.

Environment

• Introduced by fix(push): honor explicit branches and protect dirty team clones #690 (merge commit 9d3a91c), current main.