§9 acceptance: grep-zero sweep — every internal x.ai/grok identifier renamed

The PRD's first acceptance gate now holds: grep -RinE '\bx\.ai\b|grok'
crates/ --include='*.rs' → 0 matches (exempt: NOTICE and third-party
license archives, README provenance, and the required 'Based on Grok
Build Open Source' attribution, now sourced from version_attribution.txt).

Wire-visible renames (both sides in this repo, changed in lockstep):
- Auth method id 'grok.com' → 'kimi-code' (AuthMethodKind::KimiCode).
- Every x.ai/* and _x.ai/* ACP ext method and meta key → kigi/* /
  _kigi/* (~200 names; grokShell → kigiShell). Session-file replay keeps
  a read-side alias for the legacy '_x.ai/session/update' method so
  existing updates.jsonl histories load; writes emit only the new name
  (both directions test-pinned).
- Agent types grok-build* → kigi* with a documented legacy-prefix alias
  at resolution time so persisted sessions keep resolving.
- ToolNamespace/BuiltinAgentName GrokBuild* → Kigi* (wire snake_case
  kigi/kigi_concise/kigi_hashline; schema regenerated); grok_build
  implementation dirs renamed to kigi*.
- x-grok-* headers → x-kigi-*, __GROK_* sentinels → __KIGI_*, themes
  grokday/groknight → kigiday/kiginight (old persisted values fall back
  to the default theme), web_fetch allowlist xAI hosts → kimi.com +
  moonshot platforms, changelog CDN → this repo, grok-build changelog
  archives deleted.
- BYOK default endpoint removed: [endpoints] api_base_url is now truly
  optional with NO default — consumers fail fast with the flag name when
  unset (no silent x.ai egress). Mock harnesses inject it explicitly.
- System-prompt identity fixed: 'released by xAI' → 'an unofficial
  community CLI for Kimi' (template + regenerated encrypted form).

Also repaired pre-existing grok-era test debt found by the sweep: the
stale trace_classify default-model pin, the grok-pager UA label test,
pty-harness stale-binary reuse and non-hermetic moonshot routing (a PTY
test could previously reach the real api.moonshot.cn), and the outdated
oauth fixture scope key.

Gates: §9 grep 0; fmt clean; workspace check/clippy 0/0 (-D warnings);
FULL cargo test --workspace: 234 suites, 21,961 passed, 0 failed;
deny advisories ok.

crates/codegen/kigi-agent/src/prompt/context.rs

@@ -144,13 +144,13 @@ pub struct PromptContext {
     /// stdio / generic-ACP).
     #[serde(default)]
     pub is_non_interactive: bool,
-    /// Identity in the primary grok-build system prompt (`You are <label>…`).
+    /// Identity in the primary kigi system prompt (`You are <label>…`).
     /// Not the UI picker name. Defaults to [`DEFAULT_SYSTEM_PROMPT_LABEL`].
     #[serde(default = "default_system_prompt_label")]
     pub system_prompt_label: String,
 }
-/// Default identity on trim-tool-descriptions (`You are Grok released by xAI`).
-pub const DEFAULT_SYSTEM_PROMPT_LABEL: &str = "Grok";
+/// Default identity on trim-tool-descriptions (`You are Kigi released by xAI`).
+pub const DEFAULT_SYSTEM_PROMPT_LABEL: &str = "Kigi";
 fn default_system_prompt_label() -> String {
     DEFAULT_SYSTEM_PROMPT_LABEL.to_string()
 }
@@ -427,9 +427,9 @@ mod tests {
     #[test]
     fn test_placeholders_system_prompt_label_override() {
         let mut ctx = test_context();
-        ctx.system_prompt_label = "Grok Internal".into();
+        ctx.system_prompt_label = "Kigi Internal".into();
         let p = ctx.placeholders();
-        assert_eq!(p["system_prompt_label"], "Grok Internal");
+        assert_eq!(p["system_prompt_label"], "Kigi Internal");
     }
     #[test]
     fn test_missing_system_prompt_label_deserializes_to_default() {
@@ -1229,7 +1229,7 @@ mod tests {
             ("plan", plan),
         ] {
             assert!(
-                !prompt.contains("You are a Grok Build agent"),
+                !prompt.contains("You are a Kigi agent"),
                 "{name} prompt should not duplicate base template identity"
             );
         }