fix(#1356): tea login resolution fails closed on a declared git identity (#1361)

Co-authored-by: fred <[email protected]>

packages/mosaic/framework/tools/git/detect-platform.sh

@@ -180,6 +180,66 @@ raise SystemExit(1)
 PY
 }
 
+# Map a host to the instance prefix used in canonical tea login names
+# ("<instance>-<identity>"). This deliberately mirrors the _idpfx case in
+# get_gitea_token(): the two credential paths must agree on what a host is called,
+# or an agent authenticates as itself on one path and as somebody else on the other.
+gitea_instance_for_host() {
+    case "${1:-}" in
+        git.uscllc.com)      echo usc ;;
+        git.mosaicstack.dev) echo mosaicstack ;;
+        *)                   return 1 ;;
+    esac
+}
+
+# Resolve the acting git identity, same precedence as get_gitea_token() step 0.
+# Prints "<identity>\t<source>" so the caller can name the source in an error.
+resolve_git_identity() {
+    local ident src
+    ident="${MOSAIC_GIT_IDENTITY:-}"
+    src="MOSAIC_GIT_IDENTITY"
+    if [[ -z "$ident" ]]; then
+        ident="$(git config --get mosaic.gitIdentity 2>/dev/null || true)"
+        src="git config mosaic.gitIdentity"
+    fi
+    [[ -n "$ident" ]] || return 1
+    printf '%s\t%s\n' "$ident" "$src"
+}
+
+# Map a repo owner to an instance. Used only by the --repo override path, which
+# has an owner and no host. Previously lived inline in lane-brief.sh; one copy so
+# the two override callers cannot drift apart.
+gitea_instance_for_owner() {
+    local owner="${1:-}"
+    owner="${owner%%/*}"
+    case "$owner" in
+        usc|USC)            echo usc ;;
+        mosaicstack|mosaic) echo mosaicstack ;;
+        *)                  return 1 ;;
+    esac
+}
+
+# Does a login of this name exist at all? The --repo override path cannot check
+# host agreement, because it has no host.
+tea_login_exists() {
+    local login_name="$1"
+    local logins_json
+    command -v tea >/dev/null 2>&1 || return 1
+    logins_json=$(tea login list --output json 2>/dev/null) || return 1
+    TEA_LOGINS_JSON="$logins_json" python3 - "$login_name" <<'PY_INNER'
+import json, os, sys
+want = sys.argv[1]
+try:
+    logins = json.loads(os.environ.get("TEA_LOGINS_JSON", "[]"))
+except Exception:
+    raise SystemExit(1)
+for login in logins if isinstance(logins, list) else []:
+    if str(login.get("name") or login.get("Name") or "") == want:
+        raise SystemExit(0)
+raise SystemExit(1)
+PY_INNER
+}
+
 tea_login_matches_host() {
     local login_name="$1" host="$2"
     local logins_json
@@ -276,6 +336,40 @@ get_gitea_login_for_host() {
         fi
     fi
 
+    # IDENTITY LADDER (#1356). Below this point the old code took the FIRST login
+    # matching the host, which is not an identity — with 43 logins on a fleet host,
+    # ~22 match one server, so a seat with no login of its own silently acted as
+    # whichever happened to be first in ~/.config/tea/config.yml. Gate 16 depends on
+    # author != reviewer, and borrowing satisfies it mechanically while violating it
+    # in fact. The token path already refuses to borrow; this is the same refusal.
+    #
+    # Enforced ONLY when an identity is resolvable, exactly like get_gitea_token():
+    # no identity means a human at a terminal, and neither path enforces there.
+    local ident ident_src inst canon
+    if IFS=$'\t' read -r ident ident_src < <(resolve_git_identity); then
+        if inst=$(gitea_instance_for_host "$host"); then
+            canon="${inst}-${ident}"
+            if tea_login_matches_host "$canon" "$host"; then
+                echo "$canon"
+                return 0
+            fi
+            # Say which of the two it is. "No such login" when tea is simply not
+            # installed is a diagnosis of a cause that was never checked, and it
+            # sends the reader off to create a login they cannot create.
+            if ! command -v tea >/dev/null 2>&1; then
+                echo "Error: git identity '$ident' requested (via $ident_src) for host '$host', but tea is not installed," >&2
+                echo "       so no login can be resolved. Refusing to guess an identity." >&2
+                return 1
+            fi
+            echo "Error: git identity '$ident' requested (via $ident_src) for host '$host', but no tea login named '$canon' exists." >&2
+            echo "       Refusing to borrow another login. Acting as a different identity would satisfy gate 16 mechanically while violating it." >&2
+            echo "       Create it with:  ~/.config/mosaic/tools/fleet/seat-logins.sh --apply --seat $ident" >&2
+            return 1
+        fi
+        # Identity known but the host is not a Mosaic instance. Fall through: the
+        # canonical name is undefined for it, so there is nothing to enforce.
+    fi
+
     login=$(find_tea_login_for_host "$host" || true)
     if [[ -n "$login" ]]; then
         echo "$login"
@@ -351,14 +445,41 @@ raise SystemExit(1)
 PY
 }
 
+# Resolve a login for an explicit --repo override, which supplies an owner and no
+# host. Takes "owner" or "owner/repo".
+#
+# The old body fell through to get_default_tea_login(), which returns the
+# default-marked login or, failing that, the first login of ANY host — arbitrary
+# identity, chosen by config file order. That is the #1356 fail-open in its worst
+# form, because unlike the host path it does not even constrain the server.
 get_gitea_login_for_repo_override() {
-    local login
+    local owner="${1:-}"
+    local login ident ident_src inst canon
 
     if [[ -n "${GITEA_LOGIN:-}" ]]; then
         echo "$GITEA_LOGIN"
         return 0
     fi
 
+    if IFS=$'\t' read -r ident ident_src < <(resolve_git_identity); then
+        if inst=$(gitea_instance_for_owner "$owner"); then
+            canon="${inst}-${ident}"
+            if tea_login_exists "$canon"; then
+                echo "$canon"
+                return 0
+            fi
+            echo "Error: git identity '$ident' (via $ident_src) has no tea login '$canon' for owner '${owner%%/*}'." >&2
+            echo "       Create it with:  ~/.config/mosaic/tools/fleet/seat-logins.sh --apply --seat $ident" >&2
+            return 1
+        fi
+        echo "Error: git identity '$ident' (via $ident_src) is set, but owner '${owner%%/*}' maps to no known instance," >&2
+        echo "       so the login name cannot be derived. Refusing to fall back to an arbitrary login." >&2
+        echo "       Set GITEA_LOGIN to name the login explicitly." >&2
+        return 1
+    fi
+
+    # No identity: a human at a terminal. Unchanged, and the same place the token
+    # path stops enforcing.
     login=$(get_default_tea_login || true)
     if [[ -n "$login" ]]; then
         echo "$login"