docs: cut the 0.4.0 changelog section

[pdfinn]

Summary

The changelog's [Unreleased] section had not been touched since #528
(2026-08-23), leaving ~30 commits undocumented. Cutting a release on top of
that would ship notes that omit most of the cycle's security work and, worse,
omit two changes a reader has to be told about explicitly.

Renamed to 0.4.0 rather than 0.3.7: the wallet leaving experimental, a new
LLM backend, whole-/usr durability, and a removal are past a patch bump.

Changes

• [Unreleased] -> [0.4.0] - 2026-09-12.
• New Runtime tree & build section. dis/ is no longer tracked (Make the tracked runtime tree exactly what the source compiles to #559) and
  the experimental Go-on-Dis work was removed (Remove the experimental Go-on-Dis work #566) — both change what a
  clone contains, so they lead rather than sit in a footnote.
• Security rewritten for this cycle's focus: the mounts and the pathname
  stack themselves, not the control grammars above them — MREADONLY
  attenuation (fix(veltro): enforce read-only namespace mounts #586), mount boundaries across parent walks (fix(emu): preserve mount boundaries across parent walks (INFR-470) #600), the
  traversal escape (fix(veltro,emu): close the namespace traversal escape and harden delegation evidence #537), materialized runtime profiles (fix(veltro): materialize audited runtime profiles (INFR-456) #591/fix(build): sync generated MREADONLY constant #592/fix(veltro): remove campaign-only runtime hooks (INFR-466) #596/fix(veltro): remove duplicate runtime profiles (INFR-466) #598),
  the hidden audit fallback in restrictns (fix(veltro): avoid hidden audit fallback (INFR-459) #593), COW overlays keyed by path
  (fix(veltro): share COW overlays across tools by keying on path (INFR-435) #571), campaign metadata failing closed (fix(security): fail closed on campaign metadata #580), bounded lucibridge tool
  calls (fix(lucibridge): bound native tool calls #599), truthful grantable catalogue (fix(veltro): expose truthful grantable tool catalogue #544). The earlier ~40 fixes are
  retained as a trailing summary.
• New Emulator, JIT & shell reliability section (INFR-421 typecom slab,
  Linux fault reporting, devfs Fsinfo, pthread leader lifetime, sh
  waitfd).
• New Testing & compliance section (escape-room harness out of the product
  tree plus ring-fence, grind fixes, evidence scorecard).
• codex-gate maturation folded into the existing LLM backends section.

Testing

Documentation only — no code paths touched.

• Tests pass (/tests/runner.dis -v) — unaffected; verified separately
  that the tree builds and tools/verify-dis-build.sh produces all 964
  manifest modules at this base
• New tests added (if applicable) — n/a, docs only
• Tested on: macOS arm64 (build verification)

Checklist

• Code follows the existing style of the file(s) modified
• No .dis build artifacts committed from appl/ or tests/
• Documentation updated (if applicable) — this is the documentation
• No secrets, API keys, or credentials included

Design principles — none apply; this PR adds no interface, service, script, or
external fetch. Every claim in the new sections is sourced from the commit or
PR body it cites rather than inferred from the subject line.

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