M0: compilable skeleton — Kigi 0.1.0 fork surgery

Hard fork of xai-org/grok-build (Apache-2.0) re-targeted as Kigi, an
unofficial Kimi Code CLI community build.

Rename & identity
- 72 xai-*/xai-grok-* crates -> kigi-* (explicit: xai-grok-pager-bin ->
  kigi-bin [binary `kigi`], xai-grok-pager -> kigi-tui; rest mechanical);
  ptyctl, ptyctl-cli, third_party/ unchanged; proto package
  xai.grok.tools.v1 -> kigi.tools.v1
- Config home ~/.kigi (KIGI_SHARE_DIR override), env prefix GROK_* ->
  KIGI_*, `kigi --version` carries the unofficial-community-build notice
- clap identity, help text, startup banner, prompt templates rebranded
  (templates re-encrypted)

Deletions (PRD removal list #5/#6/#7/#9/#10)
- voice input (xai-grok-voice) and all TUI wiring
- telemetry: Mixpanel client, external OTel stream, Sentry, OTLP layers,
  trace/GCS/S3 upload queues (kigi-file-utils halved), workspace upload
  module & dc_log, heap-profile uploader, auth-diagnostics uploader,
  session-analytics halves of feedback; local zero-egress observability
  preserved in new kigi-log crate (unified log, --debug firehose,
  subsystem file logs, opt-in instrumentation)
- announcements (crate, remote-settings fields, TUI surfaces)
- plugin marketplace (crate, sources/browse/CTA/extensions-modal tab);
  direct plugin install/uninstall/update via kigi-agent git_install kept
- relay/gateway/assets endpoints and features (agent relay, headless
  relay transport, gateway bridge, LeaderEnvUrls); leader IPC socket now
  ~/.kigi/leader.sock + KIGI_LEADER_SOCKET, no ws-url derivation
- functional types rehomed instead of deleted: PermissionMode ->
  kigi-config-types, McpInitStrategy -> kigi-mcp, PrCreationSource ->
  session signals, TerminalDiagnostics -> kigi-pager-render, agent_id ->
  shell util

Endpoints
- kigi-env rewritten: single production KigiEndpoints {coding_api_base_url
  https://api.kimi.com/coding/v1 (KIGI_CODE_BASE_URL), oauth_host
  https://auth.kimi.com (KIGI_OAUTH_HOST), update_base_url (GitHub
  Releases API), upgrade_page_url}; GrokBuildEnvironment enum deleted

Toolchain & workspace hygiene
- Rust 1.97.0 pinned; edition 2024; full cargo update; git2 hoisted to
  workspace at 0.21 (Option->Result API migration), quick-xml 0.41
- Root Cargo.toml hand-maintained (PRD §8.1): version 0.1.0 inherited by
  all members, members sorted, unused deps pruned
- cargo-deny advisories gate (deny.toml with documented transitive
  exceptions); CI workflow (check/clippy/fmt/deny/test, macOS+Linux)
- cross-crate test seams re-gated behind `test-support` cargo feature;
  insta snapshot baselines renamed to the kigi_tui prefix
- clippy --workspace --all-targets: zero warnings; fmt clean

Fixes surfaced by the port
- updater probe/installer divergence (bin/kigi vs bin/grok symlink set)
- idle model-metadata refresh dead under KIGI_CODE_BASE_URL override
  (new is_effective_coding_endpoint_url, loopback+override aware)
- macOS symlinked-TMPDIR fixture canonicalization (foreign_sessions,
  fast-worktree); RSS measurement tests serialized via serial_test

Docs & legal (Apache §4)
- NOTICE added (upstream attribution + change statement); THIRD-PARTY
  notices sustained; kigi-tools ported-code notices extended; README,
  CONTRIBUTING, SECURITY, AGENTS.md rewritten

Out of scope for M0 (tracked): Kimi auth/inference (M1), search/fetch,
command parity, config import (M2), Computer Hub excision & final
brand-token sweep (M2), distribution & self-update rewrite (M3).

crates/codegen/kigi-log/src/sampling_log.rs

@@ -0,0 +1,70 @@
+//! Tracing layer for `target: "sampling_log"` → `~/.kigi/logs/sampling.jsonl`.
+//! Enable with `--log-sampling` or `KIGI_LOG_SAMPLING=1`.
+
+use std::sync::Mutex;
+
+use tracing::Subscriber;
+use tracing_subscriber::fmt::writer::BoxMakeWriter;
+use tracing_subscriber::layer::Layer;
+use tracing_subscriber::registry::LookupSpan;
+
+use kigi_config::kigi_home;
+
+use crate::instrumentation::{NoOpLayer, TargetFilterLayer};
+
+const ENV_VAR: &str = "KIGI_LOG_SAMPLING";
+const LOG_FILE: &str = "sampling.jsonl";
+const TARGET: &str = "sampling_log";
+
+static GUARD: std::sync::OnceLock<Mutex<Option<tracing_appender::non_blocking::WorkerGuard>>> =
+    std::sync::OnceLock::new();
+
+pub fn layer<S>() -> Box<dyn Layer<S> + Send + Sync>
+where
+    S: Subscriber + for<'span> LookupSpan<'span> + Send + Sync + 'static,
+{
+    if !std::env::var(ENV_VAR).is_ok_and(|v| matches!(v.as_str(), "1" | "true" | "on")) {
+        return Box::new(NoOpLayer::new());
+    }
+
+    let path = kigi_home().join(crate::unified_log::LOG_DIR).join(LOG_FILE);
+
+    if let Some(parent) = path.parent()
+        && let Err(e) = std::fs::create_dir_all(parent)
+    {
+        tracing::warn!("failed to create sampling log dir: {e}");
+        return Box::new(NoOpLayer::new());
+    }
+
+    if crate::unified_log::file_size(&path) >= crate::unified_log::MAX_SIZE {
+        crate::unified_log::trim_file(&path);
+    }
+
+    let file = match std::fs::OpenOptions::new()
+        .create(true)
+        .append(true)
+        .open(&path)
+    {
+        Ok(f) => f,
+        Err(e) => {
+            tracing::warn!("failed to open sampling log: {e}");
+            return Box::new(NoOpLayer::new());
+        }
+    };
+
+    let (non_blocking, guard) = tracing_appender::non_blocking(file);
+    let guard_slot = GUARD.get_or_init(|| Mutex::new(None));
+    if let Ok(mut slot) = guard_slot.lock() {
+        *slot = Some(guard);
+    }
+
+    let fmt_layer = tracing_subscriber::fmt::layer()
+        .json()
+        .with_current_span(false) // `spans` array already carries the full ancestor list
+        .with_ansi(false)
+        .with_timer(tracing_subscriber::fmt::time::UtcTime::rfc_3339())
+        .with_target(false)
+        .with_writer(BoxMakeWriter::new(non_blocking));
+
+    Box::new(TargetFilterLayer::new(fmt_layer, TARGET))
+}