docs(experts): update core-expert + kernel-overview + §10 for v1.4.x lifecycle and pre-merge gate

[Brian Krabach (bkrabach)]

Summary

Updates the in-repo expert context (agents/core-expert.md, context/kernel-overview.md) to surface recent kernel changes (v1.4.0/v1.4.1), and rewrites docs/CORE_DEVELOPMENT_PRINCIPLES.md §10 so it no longer contradicts context/release-mandate.md § Pre-Merge Gate.

This is a docs-only PR. No code changes. No version bump needed (no wheel-shipped code touched).

Why now

Two recent landings created a doc gap that PR #67's round-3 review surfaced:

1. PR feat(lifecycle): add on_session_ready() post-composition lifecycle hook #63 (on_session_ready) shipped via v1.4.1 — added a new optional second module lifecycle hook with its own contract (fork semantics, failure event, dispatch ordering, no-timeout, Python-only scope). None of this was reflected in core-expert.md or kernel-overview.md, so anyone consulting those would not know the lifecycle pair exists.
2. PR docs(release-mandate): add pre-merge gate requiring release readiness in PR #64 (release-mandate pre-merge gate) — codified the new release model (merge-is-release, in-PR readiness proof, core owner merges). core-expert.md still labeled its release mode "Post-Merge Gate" and docs/CORE_DEVELOPMENT_PRINCIPLES.md §10 still described the post-merge bump-then-tag flow. Direct readers of those files would follow the wrong process.

Adversarial review by systems-design:systems-design-critic (the "crusty old engineer" pass) confirmed both gaps as load-bearing and identified additional missed items (@core:CONTRACTS.md not referenced anywhere in core-expert.md, lifecycle signatures missing from the Module Protocols code-block listing) which are also addressed here.

What changed

agents/core-expert.md

• Renamed RELEASE Mode "Post-Merge Gate" → "Pre-Merge Gate"; rewrote body to cite release-mandate.md § Pre-Merge Gate as authoritative and explicitly state it supersedes §10
• Listed the five in-PR requirements with the same phrasing as release-mandate.md
• Added new MODULE LIFECYCLE Mode covering mount + on_session_ready; cites CONTRACTS.md; surfaces the no-timeout footgun, Python-only polyglot scope, module:on_session_ready_failed event, fork-per-session semantics
• Knowledge Base: added @core:CONTRACTS.md (was missing entirely) as the canonical cross-boundary reference; added @core:context/release-mandate.md as authoritative for the gate; clarified docs/contracts/ subdirectory as protocol-specific deep dives, not the cross-boundary map

context/kernel-overview.md

• "What the Kernel Provides" → new "Module Lifecycle" subsection naming mount() and on_session_ready() with concise descriptions and a pointer to CONTRACTS.md
• "Module Protocols" → new "Module Lifecycle" subsection with mount() and on_session_ready() signature blocks alongside the existing five protocols (was inconsistent: protocols had signatures, lifecycle didn't)

docs/CORE_DEVELOPMENT_PRINCIPLES.md §10 (full rewrite)

• Title: "Every Merge Gets a Release" → "Merge Is Release"
• Body rewritten to describe the pre-merge gate model: PR proves readiness, merge button is publish button
• Lists the five in-PR requirements (atomic version bump, Rust/Python symmetry, fresh wheel, E2E smoke test result, no [tool.uv.sources] git overrides)
• Documents who merges (core owner) and the merge-as-release flow
• Cross-references release-mandate.md as canonical
• Preserves valid prior content (the bump_version.py script details, the wheel-build workflow trigger, downstream-repo scope clause)
• Recovery section retained with explicit yank-then-fix-forward steps

Scope notes

• Per the critic, dropped a proposed update to bundle-awareness.md (foundation) — would have been context poisoning of a thin awareness pointer.
• foundation-expert and amplifier-expert get matching updates in separate PRs (one per repo).

Verification

git diff --stat main:

 agents/core-expert.md               | 80 +++++++++++++++++++++++++++++--------
 context/kernel-overview.md          | 27 +++++++++++++
 docs/CORE_DEVELOPMENT_PRINCIPLES.md | 74 ++++++++++++++++++++--------------
 3 files changed, 133 insertions(+), 48 deletions(-)

No code changed; no tests required. The expert files are reference docs loaded on demand by their respective agents.