diff --git a/.claude/hooks/session-start.sh b/.claude/hooks/session-start.sh
new file mode 100755
index 0000000..8842cc3
--- /dev/null
+++ b/.claude/hooks/session-start.sh
@@ -0,0 +1,73 @@
+#!/bin/bash
+# SPDX-License-Identifier: MPL-2.0
+# SPDX-FileCopyrightText: 2026 Jonathan D.A. Jewell <j.d.a.jewell@open.ac.uk>
+#
+# SessionStart hook — Claude Code on the web (cloud sessions).
+#
+# Cloud sessions ship cargo but NOT Erlang/Elixir, which VeriSimDB's
+# orchestration layer (elixir-orchestration) needs. This hook installs
+# Erlang+Elixir, warms the Rust workspace, and best-effort prefetches the
+# Elixir deps, so a cloud session starts ready to build and test.
+#
+# Cloud-only: a no-op on local checkouts (your machine already has the
+# toolchain). Every step is best-effort — a blocked registry or network
+# must never abort session startup.
+#
+# Network note: `mix deps.get` needs outbound access to the Hex registry
+# (repo.hex.pm / builds.hex.pm). On a restrictive "Trusted" network
+# allowlist those are blocked (HTTP 403) and skipped cleanly; on "Full"
+# network access they complete. The cargo path works on Trusted (crates.io
+# is allowlisted). For faster, cached startup, the install step is better
+# moved to the environment's Setup Script (snapshotted once) — see
+# https://code.claude.com/docs/en/claude-code-on-the-web
+set -uo pipefail
+
+[ "${CLAUDE_CODE_REMOTE:-}" != "true" ] && exit 0
+
+ROOT="${CLAUDE_PROJECT_DIR:-$PWD}"
+cd "$ROOT" || exit 0
+
+LOG="${TMPDIR:-/tmp}/verisimdb-session-start.log"
+: >"$LOG"
+log() { echo "[verisimdb] $*"; }
+run() { "$@" >>"$LOG" 2>&1; } # best-effort: failures land in the log, never abort
+
+# ── Install Erlang + Elixir (idempotent: skip when already present) ────
+# Cloud images omit BEAM. Erlang/OTP 25 from apt + a precompiled Elixir
+# 1.17 (built for OTP 25) from GitHub satisfies elixir-orchestration's
+# `elixir: "~> 1.17"` requirement.
+if ! command -v mix >/dev/null 2>&1; then
+  log "installing Erlang (apt, OTP 25) + Elixir 1.17 (GitHub)…"
+  run apt-get update -qq
+  run apt-get install -y -qq erlang-nox
+  z="${TMPDIR:-/tmp}/elixir.zip"
+  if run curl -fsSL -o "$z" \
+      https://github.com/elixir-lang/elixir/releases/download/v1.17.3/elixir-otp-25.zip; then
+    run mkdir -p /usr/local/elixir && run unzip -o "$z" -d /usr/local/elixir
+    for b in elixir elixirc mix iex; do
+      [ -f "/usr/local/elixir/bin/$b" ] && run ln -sf "/usr/local/elixir/bin/$b" /usr/local/bin/
+    done
+  fi
+fi
+
+# ── Warm the Rust workspace (works on Trusted; the core of VeriSimDB) ──
+# `cargo fetch` downloads the whole workspace's dependency tree so later
+# `cargo build` / `cargo test` are offline-capable. A full `cargo build`
+# is deliberately NOT run — the ~20-crate workspace is heavy and this hook
+# is synchronous; it compiles on first use instead.
+log "fetching Rust workspace dependencies (cargo fetch)…"
+run cargo fetch --locked || run cargo fetch
+
+# ── Best-effort: Elixir orchestration deps (needs Hex; 403 on Trusted) ─
+if command -v mix >/dev/null 2>&1 && [ -f elixir-orchestration/mix.exs ]; then
+  log "fetching Elixir deps (best-effort; needs Hex registry access)…"
+  (
+    cd elixir-orchestration || exit 0
+    run mix local.hex --force
+    run mix local.rebar --force
+    run mix deps.get
+  )
+fi
+
+log "ready (full log: $LOG)."
+exit 0
diff --git a/.claude/settings.json b/.claude/settings.json
new file mode 100644
index 0000000..ea39e04
--- /dev/null
+++ b/.claude/settings.json
@@ -0,0 +1,15 @@
+{
+  "hooks": {
+    "SessionStart": [
+      {
+        "matcher": "startup|resume",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "$CLAUDE_PROJECT_DIR/.claude/hooks/session-start.sh"
+          }
+        ]
+      }
+    ]
+  }
+}
diff --git a/REUSE.toml b/REUSE.toml
index a6e45ec..1445c1b 100644
--- a/REUSE.toml
+++ b/REUSE.toml
@@ -148,6 +148,15 @@ precedence = "aggregate"
 SPDX-FileCopyrightText = "2026 Jonathan D.A. Jewell <j.d.a.jewell@open.ac.uk>"
 SPDX-License-Identifier = "MPL-2.0"
 
+# Claude Code on the web — SessionStart hook + settings
+[[annotations]]
+path = [
+  ".claude/**",
+]
+precedence = "aggregate"
+SPDX-FileCopyrightText = "2026 Jonathan D.A. Jewell <j.d.a.jewell@open.ac.uk>"
+SPDX-License-Identifier = "MPL-2.0"
+
 # Nickel config
 [[annotations]]
 path = [