Part of the docs-migration chore (issue #708). Remove GitHub issue
numbers from inline comments, option descriptions, and rustdoc —
these are contextless noise for anyone reading the code without
access to the original discussions. Replace with prose that captures
the same rationale directly.
No functional change. Build still clean (cargo check passes).
Drops the hardcoded `nixpkgs.url = "github:NixOS/nixpkgs/nixos-25.11"`
from the meta flake renderer. meta now declares:
nixpkgs.follows = "hyperhive/nixpkgs";
nixpkgs-unstable.follows = "hyperhive/nixpkgs-unstable";
so every agent-level `inputs.<X>.inputs.nixpkgs.follows = "nixpkgs"`
resolves transitively to hyperhive's own pin. One channel decision
in the whole tree (hyperhive/flake.nix line 5), no second source
to drift.
`closes #317` invariant still holds: `nixpkgs` is a single canonical
name in the meta tree, it just resolves through hyperhive instead
of being its own root input.
Also:
- bump hyperhive/flake.nix line 5: `nixos-25.11` → `nixos-26.05`,
flake.lock relocked
- flake_check.rs fixtures bumped cosmetically (synthetic data, not
shape-affecting)
- rename + rewrite `render_flake_declares_canonical_nixpkgs` →
`render_flake_aliases_nixpkgs_to_hyperhive`; asserts the new
follows-form AND the absence of any literal `nixpkgs.url`
- drop the now-redundant `render_flake_collapses_hyperhive_nixpkgs_via_follows`
test (the old indirection it covered no longer exists)
Closes#526.
