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-markdown/src/checkpoint.rs

@@ -0,0 +1,58 @@
+//! Checkpoint types for incremental markdown rendering.
+//!
+//! This module defines types for identifying stable boundaries in markdown text
+//! where rendered output can be "frozen" and cached. Content before a checkpoint
+//! will not change regardless of what text is appended after it.
+//!
+//! # Design
+//!
+//! Checkpoints are only created at **top-level** (depth=0) block boundaries. Blocks
+//! nested inside lists, blockquotes, or tables cannot be checkpoints because the
+//! outer container might continue.
+//!
+//! # Example
+//!
+//! ```text
+//! # Heading          <- Checkpoint after this (heading at depth=0)
+//!
+//! Paragraph text.    <- Checkpoint after blank line (paragraph at depth=0)
+//!
+//! - List item        <- NO checkpoint (inside list)
+//!   ```code```       <- NO checkpoint (code block inside list)
+//! - Another item
+//!                    <- Checkpoint here (list closed at depth=0)
+//! ```
+
+/// A position in the source text where rendered content can be frozen.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct Checkpoint {
+    /// Byte offset in source text (exclusive end of frozen region).
+    /// Content in `text[..source_bytes]` can be cached.
+    pub source_bytes: usize,
+    /// Number of output lines that correspond to this checkpoint.
+    /// Lines `0..output_lines` can be frozen.
+    pub output_lines: usize,
+    /// What kind of block ended at this checkpoint.
+    pub kind: CheckpointKind,
+}
+
+/// The type of markdown block that created a checkpoint.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum CheckpointKind {
+    /// A heading (any level: h1-h6)
+    Heading,
+    /// A paragraph followed by a blank line
+    Paragraph,
+    /// A fenced or indented code block
+    CodeBlock,
+    /// A blockquote that closed at top level
+    BlockQuote,
+    /// A list (ordered or unordered) that closed at top level
+    List,
+    /// A thematic break (horizontal rule: ---, ***, ___)
+    ThematicBreak,
+    /// A table that closed at top level
+    Table,
+    /// A raw HTML block
+    HtmlBlock,
+}