R1: the CI timings measured on the runner

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EhqxQ49eCju4CzKYNjZzwT

docs/milestones/R1.md

@@ -217,6 +217,17 @@ The framework is rebuilt with our SDK settings (ADR 0006), and the rebuilt libra
 | Host tests and coverage | 49 s | 33 s |
 | Rebuilding locally with nothing changed | 77 s | 13 s |
 
-The runner's own first run after this change is still a slow one: it has no mark yet, so it rebuilds the framework once more, then keeps it.
+### Measured on the runner (pull request #76, 2026-10-07)
+
+| Run | Tools | Tests and coverage | The firmware | The whole job |
+|---|---|---|---|---|
+| Before (run 81) | 15 s | 55 s | 358 s | 434 s |
+| The first with the new workflow: no mark yet, the framework is rebuilt once more and the caches fill | 16 s | 59 s | 354 s | 431 s |
+| The next commit (only the workflow changed) | 10 s | 36 s | **51 s** | **100 s** |
+| The same commit again | 10 s | 36 s | **18 s** | **66 s** |
+
+In the 51-second run, 245 objects came from the cache and 43 were compiled: `version.cpp`, as expected, and all 42 files of `src/`, which had not changed. In the run after it, all 290 came from the cache. So the objects of `src/` made by the run that rebuilt the framework were not reusable by a normal run, and those of a normal run are: the two-pass build that rebuilds the framework compiles `src/` with something different on its command line. It costs one 51-second run after each framework rebuild, which is rare; I did not look for what differs.
+
+The firmware step with everything cached is 18 seconds: the libraries are downloaded and unpacked (4 s), the dependency scan (5 s), fetching 290 objects, the link and the image (the last 11 s). A pull request that changes a few files should land between that and 51 seconds.
 
 **What it costs:** the build cache grows by about 40 MB a run (each linked firmware is kept) and is started again past 3 GB; ccache is held to 1 GB.