fix(decoder): give the container the Canary it is supposed to run

The database mount below was one of three ways the decoder could not reach its
own oracle. The other two are here.

`run-canary` never looked in `Checked/`. It tried `Release/` then `Debug/`, and
both of those exist on this box -- an Aug 28 binary and a Jul 19 one. They boot
the game perfectly well and carry NO `audit_61` branch probe, so a probe run
against either returns zero hits that read as a finding about the game rather
than as a stale binary. Configuration is now the outer loop and location the
inner one, so a `Checked` build anywhere beats a `Release` build anywhere;
`$XENIA_BIN` still overrides everything. Measured here: `Checked` has
`audit_61_branch_probe_pcs`, `Release` and `Debug` do not.

The launcher also now says which instrumentation is missing BEFORE the run,
because the alternative is reading an empty log afterwards and guessing.

`build-canary` built `$PROJECT_DIR/xenia-canary`, which does not exist in this
container -- the source is bind-mounted at `/canary` and the launcher already
exports `XENIA_SRC=/canary`. CONTAINER-NOTES has carried that defect since
2026-08-29 with a symlink workaround and a warning to remember to delete the
symlink afterwards. It now reads `$XENIA_SRC` first, so there is nothing to
remember. Its default configuration moves Release -> Checked to match what
`run-canary` picks; the old default spent a full build on a binary nothing ran.

Two documented blockers are refuted rather than deleted, since the sequence of
wrong readings is what makes the right one checkable: the CONTAINER-NOTES
symlink dance (the warm build volume it was configured against is gone too,
removed in the 2026-09-18 cleanup, so the next build configures cleanly against
`/canary`), and `upstream-baseline.md`'s "`version.h` is never generated" --
`CMakeLists.txt` generates it at configure time now, with a stub fallback.

`decoder-loop.md` claimed the oracle was at `Linux/Release/` and that the probe
was on two side branches; both were true when written and neither is now.

Verified: five pick_bin cases against the extracted function body, and `strings`
on all three real binaries.

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

docs/agents/CONTAINER-NOTES.md

@@ -12,13 +12,20 @@ already went wrong once.
 * **The toolchain is real.** `tools/re-capture/rebuild_canary.sh` exists because
   the old box had no cmake/ninja/clang and only runtime sonames, so it hand-
   relinked object files. **Do not use it here.** Use `build-canary`.
-  🔴 **But `build-canary` does not work in this container as it stands
+  ✅ **FIXED 2026-09-21 — `build-canary` now reads `$XENIA_SRC` first**, which the
+  launcher already sets to `/canary`, so there is no symlink to make and none to
+  forget. The two paragraphs below are kept because they are how the defect was
+  found and refuted, but **neither describes the script any more.**
+
+  🔴 ~~**`build-canary` does not work in this container as it stands
   (2026-08-29).** It builds `${PROJECT_DIR:-/work}/xenia-canary`, which **does
   not exist here** — the Canary source is at **`/canary`** (`$XENIA_SRC`). The
   warm 235 MB tree at `/sylph-home/re/canary-build` is configured with
   `CMAKE_HOME_DIRECTORY=/work/xenia-canary`, also missing, and its
   `build-Release.ninja` carries **no per-file rules** — it wants to re-run CMake
-  first, which would fail on the absent source root.
+  first, which would fail on the absent source root.~~ The warm tree is gone too:
+  every `sylph-*` volume was removed in the 2026-09-18 cleanup, so the next build
+  configures from scratch against `/canary` and caches the right source root.
 
   ✅ **The conclusion drawn from all that is REFUTED (2026-08-31).** The note went
   on to say *"any Canary change is a full reconfigure against `/canary` plus a full
@@ -38,9 +45,10 @@ already went wrong once.
   warm 235 MB tree is otherwise intact and the ninja re-run resolves its rules
   from the symlink.
 
-  ⚠️ **Remove the symlink when you are done.** `/work` is the repository, and
-  `xenia-canary` is not in `.gitignore`, so it shows up as untracked and can be
-  swept into a `git add -A`.
+  ⚠️ ~~**Remove the symlink when you are done.**~~ No longer needed — but if you
+  ever make one by hand, note that `/work` is the repository and `xenia-canary`
+  is not in `.gitignore`, so it shows up as untracked and can be swept into a
+  `git add -A`.
 * **numpy and Pillow are installed.** `entities2.py`, `flight_probe.py` and the
   image oracles work. Their absence used to look like a logic bug.
 

docs/agents/decoder-loop.md

@@ -57,7 +57,7 @@ rather than left in a document you might not reach.
 |---|---|---|
 | `/image/sylpheed.pe` | the decompressed executable image | `SYLPHEED_PE` |
 | `sylpheed.db` at the repo root | the disassembly database, 337 MB | — (`zq.py` finds it; `$SYLPHEED_DB` only to override) |
-| `/canary/build/bin/Linux/Release/xenia_canary` | the built oracle, inside the `/canary` mount | — |
+| `/canary/build/bin/Linux/Checked/xenia_canary` | the built oracle, inside the `/canary` mount | — |
 | `/disc` | the extracted disc | `SYLPHEED_DISC` |
 | `/iso/game.iso` | the retail ISO Canary boots | `SYLPH_ISO` |
 | `/canary` | the Canary source, read-write | `XENIA_SRC` |
@@ -67,11 +67,16 @@ rather than left in a document you might not reach.
 says so and prints the command that builds it. Query the database with
 `python3 tools/zq.py …`, never by reading a disassembly dump.
 
-⚠️ **The built Canary carries the `RE-INPUT`/`RE-DRAW` instrumentation but NOT
-the `audit_61` guest-PC branch probe** — that lives only on
-`auto/canary-instrumentation-snapshot-2026-07-28` and `phase-a-tracing`
-(fork issue #1), so a probe run needs those two commits on `sylpheed-re` and a
-rebuild first. Verified by `strings` on the binary, not assumed.
+⚠️ **Take the oracle from `Checked/`, not `Release/`.** `Checked` is what this
+tree actually builds (optimised, with assertions); the `Release/` binary beside
+it is a stale August build with no `audit_61` probe in it. `strings` on the two
+is how that was found, and is how to check any binary before quoting a run from
+it.
+
+The `Checked` build carries all three instrumentations — `RE-INPUT`, `RE-DRAW`
+and the `audit_61` guest-PC branch probe (fork PR #2 brought the probe onto
+`sylpheed-re`; before it, the probe lived only on `phase-a-tracing`). Verified
+by `strings` on the binary, not assumed.
 
 **The `.pe` is a flat VA dump**: file offset = `VA - 0x82000000`. Reading
 `0x820A1630` is `seek(0xA1630)`. No XEX decrypt, no LZX, **no booted emulator** —

docs/re/upstream-baseline.md

@@ -19,12 +19,13 @@ The instrumented branch stops at the Stage 02 briefing under a storm of
 behind `upstream/canary_experimental` (`a5a18f5c7`); our branch carries 50 of its
 own.
 
-* **`version.h` is never generated.** The build fails on
-  `trace_writer.cc:17: fatal error: 'version.h' file not found`. Upstream's
-  `xenia-build.py` writes it from git HEAD; the container's `build-canary`
-  wrapper does not invoke it, and our tree only builds because a stale copy from
-  an old `sylpheed-re` build sits in the build directory. Regenerated by hand in
-  exactly the format that script emits.
+* ~~**`version.h` is never generated.**~~ ✅ **FIXED — `CMakeLists.txt` now
+  generates it at configure time**, calling `xenia-build.py`'s
+  `generate_version_h()` and falling back to a stub if that fails, so a
+  CMake-direct build no longer depends on a stale copy in the build directory.
+  It used to fail on `trace_writer.cc:17: fatal error: 'version.h' file not
+  found`, and the fix had to exist before the 2026-09-18 cleanup deleted the
+  build volume that was carrying that stale copy.
 * **`build-canary` reports success on a failed build.** The harness recorded
   "completed (exit code 0)" while ninja had stopped with `1 error generated`.
   Only the missing binary gave it away.