chore(release): 0.8.4

Version 0.8.3 -> 0.8.4 in pyproject.toml, __init__.py and uv.lock, and the
guard pin in [tool.uv.sources] moved from v1.3.0 to v1.4.0 (uv.lock follows
via `uv lock`: the guard's version, source and requires-dist lines, nothing
else). CHANGELOG [Unreleased] closed as [0.8.4] with K3-21's and K3-22's
entries moved as written, plus one entry for the guard pin: 1.4.0 parses a
flow sequence of plain scalars that 1.3.0 refused (26 of 28 frontmatter
blocks refused by 1.3.0, 0 of 28 by 1.4.0, on one five-document bundle).
Dependency range llm-ingestion-guard>=1.2,<2.0 unchanged.

README: the four install lines and llms.txt's one to @v0.8.4, the guard
pairing prose to v0.8.4 / v1.4.0, the pip fallback to @v1.4.0, a v0.8.4
row as the current tag (seventeen checker rules), and the suite count
(1783 collected, 1782 passed, 1 skipped) with its history extended.

No behaviour change in src/ beyond the version string.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

CHANGELOG.md

@@ -7,6 +7,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [0.8.4] — 2026-09-11
+
 ### Added
 
 - **`parent` reaches the reader (K3-21 A).** `okf consume` resolves a
@@ -43,6 +45,14 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   path repeats the document's directory in 675 bodies and moved the delivered
   set on 2 of 8 questions at the default `k` (3 of 8 at `k` 50), hit@k
   unchanged.
+- **The guard pin moves from `v1.3.0` to `v1.4.0`** (`[tool.uv.sources]`, and
+  the pip fallback in the README). Installing `@v0.8.4` gives a different
+  guard than installing `@v0.8.3`: 1.4.0 parses a flow sequence of plain
+  scalars -- `source_offset: [1, 24]`, `derived: [number]` -- where 1.3.0
+  raised "a flow sequence admits flow mappings only". Measured with both
+  guards' `parse_frontmatter` on one bundle built from the five-document
+  project: 1.3.0 refuses 26 of its 28 frontmatter blocks, 1.4.0 refuses 0 of
+  28. The dependency range `llm-ingestion-guard>=1.2,<2.0` is unchanged.
 
 ### Fixed