chore(agents): restore evidence sharing after the asset purge

Issue #49 removed game assets from git. It also, silently, removed the only
transport agents had for showing each other evidence: each agent works in its
OWN clone, so "commit the screenshot, the other one pulls it" was the mechanism,
and PROTOCOL.md's file table said so in as many words -- "evidence cited by a
finding -> git". That row sat directly above "🔴 Never commit game content",
which is how 76 MB accumulated: the two contradicted each other and the table
won, because it was the one that told you what to do.

WHAT REPLACES IT

  * one host directory, `Sylpheed/docs/re/captures/`, bind-mounted read-write
    into BOTH agents at /work/docs/re/captures. All three -- host, decoder,
    port -- see the same files live, every citation resolves, and nothing can
    reach git history. Read-write on purpose: showing each other a screenshot
    is the point.
  * PROTOCOL.md's table rewritten. Cited evidence -> present but never
    committed; derived measurements (csv/tsv/txt/log/json) -> still git, they
    are our numbers not game content; evidence that must cross MACHINES ->
    attached to the issue or PR, because a bare clone has no captures.

Verified, not assumed: container A wrote a .png there, a SEPARATE container B
read it back, the host saw it, `git status` reported 0 changes, and
`git check-ignore` named the rule.

THE CHECKER WAS RED ON EVERY CLEAN CHECKOUT

A fresh clone/worktree/CI has no captures, so it called all 134 citations
dangling and exited 1. A gate that is red before anyone changes anything is one
people learn to ignore -- the exact failure this file already carries a comment
about. It now distinguishes "no captures here" (expected, explains itself,
exit 0) from "these are missing" (real, exit 1, unchanged when assets ARE
present). Both paths tested.

ALSO
  * `sylph-decoder` no longer mounts `xenia-rs` -- retired repo, gone from disk,
    the mount pointed at nothing.
  * CONSOLIDATION.md closed: it still described captures as committed and the
    history fork as undecided. Both are settled.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

docker/decoder/sylph-decoder

@@ -122,11 +122,19 @@ docker_args() {
     # (file offset = VA - 0x82000000), which removes the need to boot the
     # emulator and scrape /dev/shm to get at it. An earlier belief that this
     # file was STALE was tested and refuted -- it is current.
-    -v "${SYLPH_XENIA_RS:-$PROJECT/xenia-rs}:/xenia-rs:ro"
     -v "${SYLPH_PE:-$PROJECT/Project Sylpheed - Arc of Deception (USA, Europe) (En,Ja).pe}:/image/sylpheed.pe:ro"
     -e "SYLPHEED_DB=/xenia-rs/sylpheed.db"
     -e "SYLPHEED_PE=/image/sylpheed.pe"
     -e "SYLPHEED_IMAGE_BASE=0x82000000"
+    # 🔴 EVIDENCE IS SHARED, NOT COMMITTED (issue #49). Each agent works in its
+    # OWN clone, so a gitignored capture written in one container is invisible to
+    # the other and to the human -- git used to be the transport and no longer is.
+    # One host directory, bind-mounted into both agents, is: all three see the
+    # same files live, every `docs/re/captures/...` citation resolves everywhere,
+    # and nothing can reach git history. Read-write on purpose -- showing each
+    # other a screenshot is the point.
+    -v "${SYLPH_CAPTURES:-$PROJECT/Sylpheed/docs/re/captures}:/work/docs/re/captures"
+
     # The shared exchange: transient files with provenance, outside git history.
     -v "sylpheed-exchange:/exchange"
     -e "PROJECT_DIR=/work"