tests: run the pytest row test_run_json_stream_fastpath in the full profiles, not 'fast' - #522

…#520, p2cx-rjfast label #522)

Brings in the two commits main gained since the last merge: the dispatch-only
fleet-post-capability workflow (#520) and the drop of the "fast" label from the
pytest row (#522, tests/cr150.d/p2cx-rjfast.cmake). No conflict; none of the 38
files of this branch is touched by either commit. The head the lab verifies and
the pull request opens from therefore contains current main.

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>

## What

Adds the `## 1.8.0 — 2026-10-27` section (with migration notes) to `CHANGELOG.md`, above `## 1.7.0`. `CHANGELOG.md` is the only file changed (+131/-0). Documentation only: no `src/`, `include/`, `docker/`, `scripts/`, `tests/` or workflow file is touched.

## Why

The engine release body is generated from git-log subjects only and carries no migration notes; the release notes users read are this file (and the GitHub release body edited from it after publish). The notes must be on main before the release dispatch.

## Content

- Compatibility and migration: exact pairing with codegen 1.8.0, regenerate C++ and relink every strategy library, no public header change, the new codegen `color` input type, the changed harness file `docker/run_json.py`.
- Faster `run_json` report handling (#517) with the measured table against 1.6.3 and 1.7.0 and the statement that the gap to 1.6.3 is not closed.
- Scratch placement restated (#518); the unused storage building block (#515; its allocation-gate sites are unreviewed, no bound claimed); a known limit (memory with never-filled pending orders, "a fix is planned for a later release").
- CI and release process: every merged change since 1.7.0 not listed above (#505-#510, #513, #514, #516, #519, #520, #522, #469, #481, #504). Every line is taken from the merged commit body; none claims a behaviour change for a tests-only or CI-only change.

Not in this commit (not on main at base `641349a`): the release gate, tmpwatch and the TvJO fix. Each gets one line from its merged PR body as a follow-up commit on this branch before this PR merges; this PR is meant to merge after those three.

## Checks

- Route: docs-only, `lab verify --via ci-only` (no sweep).
- Read as a committed diff by an independent reviewer: GO. All 18 engine commits `v1.7.0..641349a` have a bullet, none extra.
- Numbers: the #517 timings and RSS are the measurements in the #517 body; the ratios in the text were recomputed (1.77/0.36 = 4.9, 8.26/1.35 = 6.1, 8.94/5.39 = 1.66; 4.61/0.36 = 12.8, 22.31/1.35 = 16.5, 22.99/5.39 = 4.27).
- The heading date `2026-10-27` is the planned tag date and is corrected before the tag if the date moves.

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