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-crash-handler/README.md

@@ -0,0 +1,47 @@
+# kigi-crash-handler
+
+Crash handler for SIGBUS/SIGSEGV with best-effort backtrace capture.
+
+## How it works
+
+`install()` registers a `sigaction` handler. On crash it writes a binary blob (`GCRX` format) to `crash_dir/last-crash.bin` and restores the terminal via pre-computed escape sequences. The handler uses only async-signal-safe operations for file I/O, terminal restore, and re-raise.
+
+On next launch, `check_previous_crash()` reads the blob, resolves IPs to symbols via `backtrace`, writes `last-crash-report.txt`, and archives it (keeping the last 5 reports).
+
+No-ops on non-unix platforms. On musl-based Linux (release builds), the handler still records signal/address/version but skips frame capture since musl does not provide `backtrace()`.
+
+## Limitations
+
+### Frame capture is best-effort
+
+Frame capture uses two fully async-signal-safe techniques:
+1. The crash instruction pointer is extracted directly from the `ucontext_t` passed by the kernel.
+2. Additional frames are captured by walking the frame-pointer chain (RBP on x86_64, x29 on aarch64) with raw pointer reads.
+
+In release builds without `-C force-frame-pointers`, the frame-pointer chain may be incomplete or empty (the compiler omits frame pointers by default for optimization). The crash PC is always captured. In debug/dev builds, frame pointers are retained by default, producing fuller call stacks.
+
+### sigaltstack is per-thread
+
+The alternate signal stack is installed only on the thread that calls `install()`. Tokio worker threads do not inherit it. Stack overflows on worker threads will still trigger the handler (sigaction is process-wide), but without altstack protection the handler itself may fault on the overflowed stack.
+
+## Usage
+
+```rust
+use std::path::PathBuf;
+
+let crash_dir = PathBuf::from("/home/user/.myapp/crash");
+
+// check_previous_crash MUST be called before install(), because
+// install() opens last-crash.bin with O_TRUNC.
+if let Some(r) = kigi_crash_handler::check_previous_crash(&crash_dir) {
+    eprintln!("Crashed last session: {}", r.signal_name);
+    eprintln!("Report: {}", r.report_path.display());
+}
+
+// install() before any threads or async runtime — sigaltstack is per-thread.
+// Creates crash_dir if it does not exist.
+kigi_crash_handler::install(kigi_crash_handler::CrashHandlerConfig {
+    app_version: env!("CARGO_PKG_VERSION").to_string(),
+    crash_dir,
+});
+```