diff --git a/tests/functional.fish b/tests/functional.fish
deleted file mode 100644
index e4d1651..0000000
--- a/tests/functional.fish
+++ /dev/null
@@ -1,114 +0,0 @@
-# Copyright (C) 2026 Rootiest
-# SPDX-License-Identifier: AGPL-3.0-or-later
-#
-# Functional checks for foundational config behavior. Sourced inside a
-# fully-loaded, sandboxed interactive fish session by tests/run-tests.fish
-# -- see that file for the sandbox setup. Each test_* function returns 0
-# on pass, non-zero on fail; functional_test_main collects and runs them.
-
-function test_xdg_defaults
-    test -n "$XDG_CONFIG_HOME" -a -n "$XDG_CACHE_HOME" \
-        -a -n "$XDG_DATA_HOME" -a -n "$XDG_STATE_HOME"
-end
-
-function test_path_additions
-    contains -- "$HOME/.local/bin" $PATH
-end
-
-function test_cdpath
-    contains -- "$HOME/projects" $CDPATH
-end
-
-function test_vi_key_bindings
-    test "$fish_key_bindings" = fish_vi_key_bindings
-end
-
-function test_abbreviations_loaded
-    abbr -q n
-end
-
-function test_core_functions_defined
-    for f in cat logs config-help fish-deps check_fish_deps config-settings
-        if not functions -q $f
-            echo "    missing function: $f"
-            return 1
-        end
-    end
-end
-
-function test_exit_rewired
-    functions -q exit
-    and functions exit | string match -q '*smart_exit*'
-end
-
-function test_op_registry_lookup
-    functions -q __fish_config_op_registry_lookup
-    or return 1
-    set -l tags (__fish_config_op_registry_lookup config cdpath)
-    test $status -eq 0 -a (count $tags) -gt 0
-end
-
-function test_privacy_variables
-    test "$DO_NOT_TRACK" = "1" -a "$DISABLE_TELEMETRY" = "1"
-end
-
-function test_privacy_op_registry_lookup
-    functions -q __fish_config_op_registry_lookup
-    or return 1
-    set -l tags (__fish_config_op_registry_lookup config privacy)
-    test $status -eq 0 -a "$tags" = "overrides/privacy"
-end
-
-function test_op_enabled_fail_open
-    # An identity/site pair with no registry entry must resolve to
-    # enabled -- the documented fail-open default.
-    __fish_config_op_enabled __fish_config_test_never_registered somesite
-end
-
-function test_greeting_function_defined
-    functions -q fish_greeting
-end
-
-function test_agents_vault_defined
-    for f in agents-vault _agents_vault_dir _agents_repo_slug \
-        _agents_repo_ensure_symlink _agents_repo_sync \
-        _agents_repo_install_tools
-        if not functions -q $f
-            echo "    missing function: $f"
-            return 1
-        end
-    end
-end
-
-function test_wrappers_call_agents_vault
-    functions -q claude; or return 1
-    functions claude | string match -q '*agents-vault*'; or return 1
-    functions -q agy; or return 1
-    functions agy | string match -q '*agents-vault*'
-end
-
-function test_vault_dir_honors_override
-    set -l saved
-    set -q __fish_agent_vault_dir; and set saved $__fish_agent_vault_dir
-    set -g __fish_agent_vault_dir /tmp/vault-override-check
-    set -l got (_agents_vault_dir)
-    set -e __fish_agent_vault_dir
-    test (count $saved) -gt 0; and set -g __fish_agent_vault_dir $saved
-    test "$got" = /tmp/vault-override-check
-end
-
-function functional_test_main
-    set -l names (functions -a | string match 'test_*' | sort)
-    set -l failed 0
-    for name in $names
-        if $name
-            echo "  PASS  $name"
-        else
-            echo "  FAIL  $name"
-            set failed (math $failed + 1)
-        end
-    end
-    echo ""
-    echo (math (count $names) - $failed)"/"(count $names)" passed"
-    return $failed
-end
diff --git a/tests/lib.fish b/tests/lib.fish
new file mode 100644
index 0000000..2edfc91
--- /dev/null
+++ b/tests/lib.fish
@@ -0,0 +1,62 @@
+#!/usr/bin/env fish
+# Copyright (C) 2026 Rootiest
+# SPDX-License-Identifier: AGPL-3.0-or-later
+#
+# Shared assertion and reporting core for tests/test-*.fish.
+#
+# One assertion: `check <label> <want> <got>`, string equality. Status
+# assertions use the two-line form, which is the point -- it can say "I
+# expected exactly 1", where a pass/fail predicate can only say "non-zero":
+#
+#     __fish_config_op_cascade __probe_cat
+#     check "all unset -> enabled" 0 $status
+#
+# That distinction matters here: __fish_variable_check returns four distinct
+# codes (0 truthy, 1 falsy, 2 unset/empty, 3 unrecognized) and the cascade's
+# behavior depends on telling 2 and 3 apart from 1.
+#
+# Boolean assertions use the idiom the vault suite already uses throughout:
+#
+#     check "label" true (some-test; and echo true; or echo false)
+
+set -g TESTS_RUN 0
+set -g TESTS_FAILED 0
+
+# The driver always sets this; the fallback is for running a suite by hand.
+if set -q FISH_CONFIG_TEST_ROOT
+    set -g repo_root $FISH_CONFIG_TEST_ROOT
+else
+    set -g repo_root (realpath (dirname (status filename))/..)
+end
+
+function section
+    echo ""
+    echo "== $argv[1] =="
+end
+
+function check --argument-names label want got
+    set -g TESTS_RUN (math $TESTS_RUN + 1)
+    if test "$want" = "$got"
+        echo "  PASS  $label"
+    else
+        echo "  FAIL  $label"
+        echo "        want: $want"
+        echo "        got:  $got"
+        set -g TESTS_FAILED (math $TESTS_FAILED + 1)
+    end
+end
+
+function report
+    echo ""
+    echo (math $TESTS_RUN - $TESTS_FAILED)"/$TESTS_RUN passed"
+    if set -q FISH_CONFIG_TEST_COUNTS
+        echo "$TESTS_RUN $TESTS_FAILED" >>$FISH_CONFIG_TEST_COUNTS
+    end
+    # Explicit terminal status, never a trailing `if` (AGENTS.md item 5).
+    # This is form, not a bug fix: fish clamps `exit`/`return` to 255 rather
+    # than wrapping mod 256, so `exit $TESTS_FAILED` could not have produced
+    # a false green. Verified: `fish -c 'exit 256'` -> 255, while
+    # `sh -c 'exit 256'` -> 0. A boolean is still the right shape -- it
+    # composes with `and`/`or`, which a raw count does not.
+    test $TESTS_FAILED -eq 0
+end
diff --git a/tests/run-tests.fish b/tests/run-tests.fish
index 59bc260..7379bf4 100755
--- a/tests/run-tests.fish
+++ b/tests/run-tests.fish
@@ -4,15 +4,19 @@
 #
 # CI test runner for this fish configuration.
 #   1. Syntax-lints every tracked .fish file (fish -n).
-#   2. Copies the config-relevant files into a throwaway sandbox (never
-#      the live checkout -- this repo doubles as a real ~/.config/fish,
-#      so a symlinked sandbox would let universal-variable writes like
-#      first-run's escape into the real, gitignored fish_variables file)
-#      and loads it as an isolated interactive session.
-#   3. Runs the functional checks in tests/functional.fish inside that
-#      loaded session.
-#   4. Runs tests/test-agents-vault.fish as its own process; that suite
-#      builds its own throwaway repos and needs no loaded config.
+#   2. Discovers tests/test-*.fish and reads the mode each suite declares
+#      in its own header (`# MODE: isolated` or `# MODE: in-session`).
+#   3. Runs each isolated suite as its own --no-config fish process with
+#      throwaway XDG dirs.
+#   4. Sources every in-session suite into ONE sandboxed interactive fish
+#      session built from a copy of this config (never the live checkout
+#      -- this repo doubles as a real ~/.config/fish, so a symlinked
+#      sandbox would let universal-variable writes like first-run's escape
+#      into the real, gitignored fish_variables file).
+#   5. Sums the per-suite assertion counts and reports a total.
+#
+# Assertions come from tests/lib.fish (section/check/report); suites are
+# never special-cased here by name.
 #
 # Usage: fish tests/run-tests.fish
 
@@ -42,61 +46,154 @@ if test $lint_failed -ne 0
     set overall_failed 1
 end
 
-# ---- Phase 2: isolated load + functional checks --------------------------
+# ---- Phase 2: discover suites --------------------------------------------
+# Mode is declared by the suite, not by this driver. Detection is
+# case-insensitive so a near-miss like "# Mode: in-session" is caught rather
+# than silently read as "no marker"; the comparison is exact so only the two
+# real spellings are accepted. Absence means isolated, the safe default -- a
+# suite that forgets the marker gets its own clean process instead of being
+# injected into a loaded session, and no typo can ever promote a suite into
+# in-session. Duplicate markers resolve first-match-wins.
+set -l isolated_suites
+set -l session_suites
+for f in (find $script_dir -name 'test-*.fish' | sort)
+    set -l decl (grep -im1 '^# *mode:' $f)
+    if test -z "$decl"
+        set -a isolated_suites $f
+    else if test "$decl" = "# MODE: in-session"
+        set -a session_suites $f
+    else if test "$decl" = "# MODE: isolated"
+        set -a isolated_suites $f
+    else
+        echo "  FAIL  "(basename $f)": unrecognized mode declaration: $decl" >&2
+        set overall_failed 1
+    end
+end
+
+set -l counts (mktemp)
+
+# ---- Phase 3: isolated suites --------------------------------------------
+# HOME is deliberately NOT overridden here. Read this before "improving" it.
+#
+# Overriding XDG_CONFIG_HOME/XDG_DATA_HOME plus --no-config is what makes these
+# runs isolated: the universal-variable file fish can reach is a fresh empty
+# one, and no config.fish/conf.d is loaded. Without that, an "isolated" suite
+# runs against the user's LIVE config and real universal variables -- this repo
+# doubles as a real ~/.config/fish -- so a guard test doing
+# `set -e __fish_config_op_logging` would erase a real universal variable out of
+# the running shell. Measured: $__fish_config_op_registry_keys has 65 entries
+# under a plain `fish`, 0 under `fish --no-config`.
+#
+# `env -i HOME=$sandbox` was tried and REJECTED. It looks strictly more
+# hermetic, but test-agents-vault.fish's hermeticity floor snapshots the real
+# $HOME/.claude/memory and $HOME/.gemini/antigravity-cli and asserts them
+# unchanged at the end. Point HOME at a sandbox and both snapshots read "absent"
+# before and after: the assertions still pass while asserting nothing. A change
+# that turns a real assertion into a tautology without turning anything red is
+# the worst failure mode a test harness has. Keeping HOME real is what keeps
+# those two assertions biting.
+#
+# Overriding XDG_DATA_HOME is a hermeticity gain on top of the isolation:
+# _agents_vault_dir falls back to
+# ${XDG_DATA_HOME:-$HOME/.local/share}/agent-vault, so a vault path that no test
+# overrode lands in a temp dir instead of the user's real ~/.local/share.
+for suite in $isolated_suites
+    echo ""
+    echo "== "(string replace $repo_root/ '' $suite)" =="
+    set -l xdg (mktemp -d)
+    env XDG_CONFIG_HOME=$xdg/cfg XDG_DATA_HOME=$xdg/data \
+        FISH_CONFIG_TEST_ROOT=$repo_root FISH_CONFIG_TEST_COUNTS=$counts \
+        fish --no-config $suite
+    if test $status -ne 0
+        set overall_failed 1
+    end
+    command rm -rf $xdg
+end
+
+# ---- Phase 4: in-session suites ------------------------------------------
+# All in-session suites share ONE sandboxed interactive session: building it
+# (copying the config, starting fish -i) is the expensive part.
+#
+# The config is COPIED, never symlinked. This repo doubles as a real
+# ~/.config/fish, so a symlinked sandbox would let universal-variable writes
+# like first-run's escape into the real, gitignored fish_variables file.
+if test (count $session_suites) -gt 0
+    echo ""
+    echo "== Sandboxed load + session checks =="
+
+    set -l sandbox (mktemp -d)
+    set -l sandbox_cfg $sandbox/xdgcfg/fish
+    mkdir -p $sandbox_cfg
+    # path-setup only adds directories that already exist (fish_add_path is a
+    # no-op on missing paths), so give it $HOME/.local/bin to find.
+    mkdir -p $sandbox/home/.local/bin
+
+    # Every utility below goes through `command`. This driver runs under the
+    # very config it tests, which shadows these: `cp` is an alias for `cp -i`,
+    # `rm` is a trash wrapper, `cat` resolves to bat. Only `cp` is an actual
+    # hazard today -- `-i` on a non-empty destination reads EOF in a
+    # non-interactive runner and SILENTLY SKIPS the copy while exiting 0,
+    # which would leave the sandbox missing config files and report success.
+    # `rm -rf` and `cat` were measured and behave correctly as-is (the rm
+    # wrapper bails to `command rm` on any non-recursive flag, so -rf really
+    # deletes and does not trash). Prefixed anyway: a test runner must not
+    # depend on the configuration under test.
+    command cp $repo_root/config.fish $sandbox_cfg/
+    test -f $repo_root/fish_plugins
+    and command cp $repo_root/fish_plugins $sandbox_cfg/
+    for d in functions conf.d completions integrations themes data
+        test -d $repo_root/$d
+        and command cp -r $repo_root/$d $sandbox_cfg/
+    end
+
+    set -l srcs
+    for s in $session_suites
+        set -a srcs "source $s;"
+    end
+
+    set -l err_file (mktemp)
+    env -i \
+        HOME=$sandbox/home \
+        XDG_CONFIG_HOME=$sandbox/xdgcfg \
+        PATH="$PATH" \
+        TERM=xterm \
+        __fish_config_op_autoexec=off \
+        FISH_CONFIG_TEST_ROOT=$repo_root \
+        FISH_CONFIG_TEST_COUNTS=$counts \
+        fish -i -c "source $repo_root/tests/lib.fish; $srcs report" \
+        2>$err_file
+    set -l session_status $status
+
+    set -l stderr_out (command cat $err_file)
+    command rm -rf $sandbox $err_file
+
+    if test -n "$stderr_out"
+        # Diagnostic only, not a gate: on machines with vendor fish configs
+        # (e.g. CachyOS's cachyos-fish-config, which this repo's config.fish
+        # sources when present) unrelated vendor warnings can land here. Real
+        # breakage in this repo's own code is caught by the assertions.
+        echo "  Session stderr output (informational):"
+        printf '%s\n' $stderr_out
+    end
+
+    if test $session_status -ne 0
+        set overall_failed 1
+    end
+end
+
+# ---- Phase 5: totals -----------------------------------------------------
+set -l total_run 0
+set -l total_failed 0
+for line in (command cat $counts)
+    set -l parts (string split ' ' -- $line)
+    set total_run (math $total_run + $parts[1])
+    set total_failed (math $total_failed + $parts[2])
+end
+command rm -f $counts
+
 echo ""
-echo "== Sandboxed load + functional checks =="
-
-set -l sandbox (mktemp -d)
-set -l sandbox_cfg $sandbox/xdgcfg/fish
-mkdir -p $sandbox_cfg
-# path-setup only adds directories that already exist (fish_add_path is a
-# no-op on missing paths), so give it $HOME/.local/bin to find.
-mkdir -p $sandbox/home/.local/bin
-
-cp $repo_root/config.fish $sandbox_cfg/
-test -f $repo_root/fish_plugins
-and cp $repo_root/fish_plugins $sandbox_cfg/
-for d in functions conf.d completions integrations themes data
-    test -d $repo_root/$d
-    and cp -r $repo_root/$d $sandbox_cfg/
-end
-
-set -l err_file (mktemp)
-env -i \
-    HOME=$sandbox/home \
-    XDG_CONFIG_HOME=$sandbox/xdgcfg \
-    PATH="$PATH" \
-    TERM=xterm \
-    __fish_config_op_autoexec=off \
-    fish -i -c "source $repo_root/tests/functional.fish; functional_test_main" \
-    2>$err_file
-set -l functional_status $status
-
-set -l stderr_out (cat $err_file)
-rm -rf $sandbox $err_file
-
-if test -n "$stderr_out"
-    # Diagnostic only, not a gate: on machines with vendor fish configs
-    # (e.g. CachyOS's cachyos-fish-config, which this repo's config.fish
-    # sources when present) unrelated vendor warnings can land here. Real
-    # breakage in this repo's own code is caught by the assertions below.
-    echo "  Session stderr output (informational):"
-    printf '%s\n' $stderr_out
-end
-
-if test $functional_status -ne 0
-    set overall_failed 1
-end
-
-# ---- Phase 3: hermetic vault helper tests --------------------------------
-# Run as its own fish process rather than inside the sandboxed session:
-# the suite builds its own throwaway git repos and binds the vault, claude
-# and agy roots to them, so it needs no loaded config and must never see
-# the real ~/.claude.
-echo ""
-echo "== Vault helper tests =="
-fish $repo_root/tests/test-agents-vault.fish
-if test $status -ne 0
+echo "TOTAL: "(math $total_run - $total_failed)"/$total_run assertions passed"
+if test $total_failed -ne 0
     set overall_failed 1
 end
 
diff --git a/tests/test-agents-vault.fish b/tests/test-agents-vault.fish
index 0d85e6d..5628e1f 100644
--- a/tests/test-agents-vault.fish
+++ b/tests/test-agents-vault.fish
@@ -8,12 +8,9 @@
 #
 # Usage: fish tests/test-agents-vault.fish
 
-set -l here (realpath (dirname (status filename)))
-set -g repo_root (realpath $here/..)
+source (realpath (dirname (status filename)))/lib.fish
 set -p fish_function_path $repo_root/functions
 
-set -g TESTS_RUN 0
-set -g TESTS_FAILED 0
 set -g TMPDIRS
 
 # The suite is hermetic against $HOME and ~/.claude, but it was not
@@ -50,18 +47,6 @@ set -gx GIT_CONFIG_VALUE_0 false
 set -gx GIT_CONFIG_KEY_1 init.defaultBranch
 set -gx GIT_CONFIG_VALUE_1 main
 
-function check --argument-names label want got
-    set -g TESTS_RUN (math $TESTS_RUN + 1)
-    if test "$want" = "$got"
-        echo "  PASS  $label"
-    else
-        echo "  FAIL  $label"
-        echo "        want: $want"
-        echo "        got:  $got"
-        set -g TESTS_FAILED (math $TESTS_FAILED + 1)
-    end
-end
-
 # Failure injection that survives uid 0.
 #
 # These fixtures used to force a failure with `chmod 500` on a parent
@@ -1995,6 +1980,4 @@ set -e __fish_agent_vault_claude_home
 set -e __fish_agent_vault_agy_root
 
 cleanup
-echo ""
-echo (math $TESTS_RUN - $TESTS_FAILED)"/$TESTS_RUN passed"
-exit $TESTS_FAILED
+report
diff --git a/tests/test-guards.fish b/tests/test-guards.fish
new file mode 100644
index 0000000..b41423d
--- /dev/null
+++ b/tests/test-guards.fish
@@ -0,0 +1,331 @@
+#!/usr/bin/env fish
+# Copyright (C) 2026 Rootiest
+# SPDX-License-Identifier: AGPL-3.0-or-later
+#
+# Table-driven coverage of the opinionated-component guard system:
+# __fish_variable_check, __fish_config_op_cascade,
+# __fish_config_op_registry_lookup and __fish_config_op_enabled.
+#
+# Runs isolated (no `# MODE:` marker, which means isolated): the driver gives
+# this process temp XDG dirs and --no-config, so there is no loaded config and
+# no universal variables. That is load-bearing in both directions --
+#
+#   * these cases `set -e` real guard variable names, including
+#     __fish_config_op_logging and __fish_config_opinionated. Under a plain
+#     `fish` those erase from the innermost scope holding the variable, which
+#     for a user with the variable set universally means destroying a real
+#     universal variable. The temp XDG_CONFIG_HOME is what makes that
+#     impossible.
+#   * the two `set -p` / `source` lines below are what make the FORK's code the
+#     code under test. Their failure modes differ and the difference matters:
+#     forgetting the fish_function_path prepend fails LOUDLY (the guard
+#     functions are unresolvable under --no-config and a call exits 127, which
+#     can never equal an expected 0/1/2/3, so every case turns red), while
+#     forgetting the registry source fails SILENTLY (__fish_config_op_enabled
+#     fail-opens on a missing entry, so a third of the table would pass for
+#     entirely the wrong reason). Hence the explicit precondition below.
+
+source (realpath (dirname (status filename)))/lib.fish
+set -p fish_function_path $repo_root/functions
+source $repo_root/conf.d/__fish_config_op_registry.fish
+
+section "guards: preconditions"
+
+check "the fork's registry is loaded" 65 (count $__fish_config_op_registry_keys)
+
+section "__fish_variable_check: truthy"
+
+for v in 1 true yes on y Y TRUE ON
+    set -g __probe_v $v
+    __fish_variable_check __probe_v
+    check "truthy '$v' -> 0" 0 $status
+end
+
+section "__fish_variable_check: falsy"
+
+for v in 0 false no off n OFF FALSE
+    set -g __probe_v $v
+    __fish_variable_check __probe_v
+    check "falsy '$v' -> 1" 1 $status
+end
+
+section "__fish_variable_check: neither"
+
+set -e __probe_v
+__fish_variable_check __probe_v
+check "unset -> 2" 2 $status
+
+set -g __probe_v ""
+__fish_variable_check __probe_v
+check "empty string -> 2" 2 $status
+
+set -g __probe_v banana
+__fish_variable_check __probe_v
+check "unrecognized -> 3" 3 $status
+
+__fish_variable_check
+check "no argument -> 2" 2 $status
+
+set -g __probe_v a b
+__fish_variable_check __probe_v
+check "multi-element list -> 3" 3 $status
+set -e __probe_v
+
+section "cascade: category only"
+
+# Invented variable names the real config can never set, so nothing ambient can
+# perturb these -- only the C5 and master cases below need real names.
+set -e __fish_config_opinionated __probe_cat __probe_cat_sub
+
+__fish_config_op_cascade __probe_cat
+check "all unset -> enabled" 0 $status
+
+set -g __probe_cat 0
+__fish_config_op_cascade __probe_cat
+check "category falsy -> disabled" 1 $status
+
+set -g __probe_cat 1
+__fish_config_op_cascade __probe_cat
+check "category truthy -> enabled" 0 $status
+
+set -g __probe_cat garbage
+__fish_config_op_cascade __probe_cat
+check "category unrecognized defers to master -> enabled" 0 $status
+set -e __probe_cat
+
+section "cascade: subcategory beats category"
+
+set -g __probe_cat 0
+set -g __probe_cat_sub 1
+__fish_config_op_cascade __probe_cat __probe_cat_sub
+check "sub on, category off -> enabled" 0 $status
+
+set -g __probe_cat 1
+set -g __probe_cat_sub 0
+__fish_config_op_cascade __probe_cat __probe_cat_sub
+check "sub off, category on -> disabled" 1 $status
+
+set -e __probe_cat_sub
+set -g __probe_cat 0
+__fish_config_op_cascade __probe_cat __probe_cat_sub
+check "sub unset, category off -> disabled" 1 $status
+
+set -g __probe_cat_sub garbage
+__fish_config_op_cascade __probe_cat __probe_cat_sub
+check "sub unrecognized defers, category off -> disabled" 1 $status
+set -e __probe_cat __probe_cat_sub
+
+__fish_config_op_cascade __probe_cat ""
+check "empty subcategory argument -> category-only chain" 0 $status
+
+section "cascade: the master is an off switch only"
+
+set -g __fish_config_opinionated 0
+__fish_config_op_cascade __probe_cat
+check "master off, category unset -> disabled" 1 $status
+
+set -g __probe_cat 1
+__fish_config_op_cascade __probe_cat
+check "master off, category on -> enabled" 0 $status
+set -e __probe_cat
+
+set -g __fish_config_opinionated 1
+__fish_config_op_cascade __probe_cat
+check "master on, category unset -> enabled" 0 $status
+
+set -g __fish_config_opinionated garbage
+__fish_config_op_cascade __probe_cat
+check "master unrecognized, category unset -> enabled" 0 $status
+set -e __fish_config_opinionated
+
+section "cascade: C5 logging is opt-in"
+
+# Uses the REAL __fish_config_op_logging name because the opt-in list lives
+# inside the cascade keyed on it. AGENTS.md: "C5 is opt-in (do not 'fix' this)"
+# -- unset or unrecognized means off, and the master switch cannot enable it.
+# If any of these three fail, that is a real defect: record it in
+# JOB-BRIEF-FINDINGS.md, do not repair the guard.
+set -e __fish_config_op_logging __fish_config_opinionated
+
+__fish_config_op_cascade __fish_config_op_logging
+check "C5 unset -> disabled" 1 $status
+
+set -g __fish_config_opinionated 1
+__fish_config_op_cascade __fish_config_op_logging
+check "C5 unset + master truthy -> still disabled" 1 $status
+set -e __fish_config_opinionated
+
+set -g __fish_config_op_logging garbage
+__fish_config_op_cascade __fish_config_op_logging
+check "C5 unrecognized is not consent -> disabled" 1 $status
+
+set -g __fish_config_op_logging on
+__fish_config_op_cascade __fish_config_op_logging
+check "C5 explicit truthy -> enabled" 0 $status
+
+set -g __fish_config_op_logging off
+__fish_config_op_cascade __fish_config_op_logging
+check "C5 explicit falsy -> disabled" 1 $status
+set -e __fish_config_op_logging
+
+section "cascade: C5 subcategories inherit opt-in"
+
+# The opt-in check reads chain[-1], which is always the CATEGORY variable, so
+# nesting inherits "off unless explicit" with no per-subcategory special case.
+set -e __fish_config_op_logging_terminal_capture
+
+__fish_config_op_cascade __fish_config_op_logging __fish_config_op_logging_terminal_capture
+check "C5 sub unset, C5 unset -> disabled" 1 $status
+
+set -g __fish_config_op_logging_terminal_capture 1
+__fish_config_op_cascade __fish_config_op_logging __fish_config_op_logging_terminal_capture
+check "C5 sub explicit truthy -> enabled" 0 $status
+
+set -g __fish_config_op_logging_terminal_capture 0
+set -g __fish_config_op_logging on
+__fish_config_op_cascade __fish_config_op_logging __fish_config_op_logging_terminal_capture
+check "C5 sub falsy, C5 truthy -> disabled" 1 $status
+set -e __fish_config_op_logging_terminal_capture __fish_config_op_logging
+
+section "registry lookup"
+
+__fish_config_op_registry_lookup cat "" >/dev/null
+check "known unsited key found" 0 $status
+
+set -l t (__fish_config_op_registry_lookup cat "")
+check "cat's tags" aliases/filesystem "$t"
+
+__fish_config_op_registry_lookup nosuchthing "" >/dev/null
+check "unknown identity -> not found" 1 $status
+
+set -l t2 (__fish_config_op_registry_lookup config cdpath)
+check "sited key config:cdpath" overrides/environment "$t2"
+
+# The key is the identity:site PAIR, not the identity alone.
+__fish_config_op_registry_lookup cat wrongsite >/dev/null
+check "known identity, wrong site -> not found" 1 $status
+
+section "op_enabled: against the real registry"
+
+set -e __fish_config_op_aliases __fish_config_op_aliases_filesystem
+set -e __fish_config_opinionated
+
+__fish_config_op_enabled cat
+check "cat, nothing set -> enabled" 0 $status
+
+__fish_config_op_enabled cat.fish
+check "a .fish suffix is stripped" 0 $status
+
+set -g __fish_config_op_aliases 0
+__fish_config_op_enabled cat
+check "cat, aliases off -> disabled" 1 $status
+
+set -g __fish_config_op_aliases_filesystem 1
+__fish_config_op_enabled cat
+check "cat, aliases off but its subcategory on -> enabled" 0 $status
+set -e __fish_config_op_aliases __fish_config_op_aliases_filesystem
+
+# Fail-open: an unclassified identity, or one whose doc header has no
+# # COMPONENT section, resolves to enabled. This is what keeps user-authored
+# and third-party functions unaffected.
+__fish_config_op_enabled __totally_unregistered somesite
+check "no registry entry -> fail open" 0 $status
+
+section "op_enabled: always/* and AND, via a synthetic registry"
+
+# Why this fixture exists, so nobody deletes it as redundant:
+#
+# The generated registry has 65 entries, EVERY ONE carrying exactly one tag,
+# and contains no always/on or always/off anywhere (measured 2026-09-07
+# against conf.d/__fish_config_op_registry.fish). So three documented
+# semantics -- always/off, always/on, and AND-across-tags -- have no reachable
+# case in production data and would otherwise go completely untested.
+#
+# The registry is just two global lists, and in isolated mode nothing else in
+# this process reads them, so overriding them is free.
+set -g __fish_config_op_registry_keys "syn_on:" "syn_off:" "syn_and:" "syn_bare:" "syn_multi:"
+set -g __fish_config_op_registry_values \
+    "always/on" \
+    "always/off" \
+    "aliases/filesystem integrations/notifications" \
+    "aliases" \
+    "always/off always/on"
+
+set -e __fish_config_op_aliases __fish_config_op_integrations __fish_config_opinionated
+
+__fish_config_op_enabled syn_off
+check "always/off -> disabled" 1 $status
+
+set -g __fish_config_op_aliases 1
+__fish_config_op_enabled syn_off
+check "always/off ignores an enabled category" 1 $status
+set -e __fish_config_op_aliases
+
+__fish_config_op_enabled syn_on
+check "always/on -> enabled" 0 $status
+
+set -g __fish_config_op_aliases 0
+__fish_config_op_enabled syn_on
+check "always/on short-circuits a disabled category" 0 $status
+set -e __fish_config_op_aliases
+
+__fish_config_op_enabled syn_multi
+check "always/off beats always/on" 1 $status
+
+section "op_enabled: AND across tagged sub-categories"
+
+__fish_config_op_enabled syn_and
+check "both categories default -> enabled" 0 $status
+
+set -g __fish_config_op_aliases 0
+__fish_config_op_enabled syn_and
+check "first tag's category off -> disabled" 1 $status
+set -e __fish_config_op_aliases
+
+set -g __fish_config_op_integrations 0
+__fish_config_op_enabled syn_and
+check "second tag's category off -> disabled" 1 $status
+set -e __fish_config_op_integrations
+
+set -g __fish_config_op_aliases 1
+set -g __fish_config_op_integrations 1
+__fish_config_op_enabled syn_and
+check "both explicitly on -> enabled" 0 $status
+set -e __fish_config_op_aliases __fish_config_op_integrations
+
+section "op_enabled: a tag with no slash"
+
+# Degenerate but harmless: with no '/', $parts[2] is empty and the derived
+# subcategory name gets a trailing underscore. That name is simply always
+# unset, so the chain falls through to the category. Pinned so a future reader
+# does not mistake it for a bug.
+__fish_config_op_enabled syn_bare
+check "bare tag 'aliases' -> enabled by default" 0 $status
+
+set -g __fish_config_op_aliases 0
+__fish_config_op_enabled syn_bare
+check "bare tag honors its category" 1 $status
+set -e __fish_config_op_aliases
+
+section "op_enabled: C5 through the guard"
+
+# The path production code actually takes, as opposed to calling the cascade
+# directly. Same rule: unset means off and the master cannot enable it.
+set -g __fish_config_op_registry_keys "syn_log:"
+set -g __fish_config_op_registry_values "logging/terminal-capture"
+set -e __fish_config_op_logging __fish_config_op_logging_terminal_capture
+
+__fish_config_op_enabled syn_log
+check "C5-tagged component, nothing set -> disabled" 1 $status
+
+set -g __fish_config_opinionated 1
+__fish_config_op_enabled syn_log
+check "C5-tagged component + master truthy -> still disabled" 1 $status
+set -e __fish_config_opinionated
+
+set -g __fish_config_op_logging 1
+__fish_config_op_enabled syn_log
+check "C5-tagged component + explicit C5 on -> enabled" 0 $status
+set -e __fish_config_op_logging
+
+report
diff --git a/tests/test-session.fish b/tests/test-session.fish
new file mode 100644
index 0000000..a7f4e09
--- /dev/null
+++ b/tests/test-session.fish
@@ -0,0 +1,62 @@
+# Copyright (C) 2026 Rootiest
+# SPDX-License-Identifier: AGPL-3.0-or-later
+#
+# MODE: in-session
+#
+# Functional checks for foundational config behavior. Sourced by
+# tests/run-tests.fish into a fully-loaded, sandboxed interactive fish
+# session -- see that file for the sandbox setup. Assertions here are the
+# ones that genuinely need a loaded config; anything testable against a
+# single function belongs in an isolated suite instead.
+
+section "session: environment"
+
+check "XDG vars are all set" true (test -n "$XDG_CONFIG_HOME" -a -n "$XDG_CACHE_HOME" -a -n "$XDG_DATA_HOME" -a -n "$XDG_STATE_HOME"; and echo true; or echo false)
+check "PATH includes ~/.local/bin" true (contains -- "$HOME/.local/bin" $PATH; and echo true; or echo false)
+check "CDPATH includes ~/projects" true (contains -- "$HOME/projects" $CDPATH; and echo true; or echo false)
+check "vi key bindings active" fish_vi_key_bindings "$fish_key_bindings"
+check "abbreviations loaded" true (abbr -q n; and echo true; or echo false)
+check "privacy variables set" true (test "$DO_NOT_TRACK" = 1 -a "$DISABLE_TELEMETRY" = 1; and echo true; or echo false)
+
+section "session: functions"
+
+set -l missing
+for f in cat logs config-help fish-deps check_fish_deps config-settings
+    functions -q $f; or set -a missing $f
+end
+check "core functions defined" "" "$missing"
+
+check "exit is rewired to smart_exit" true (functions -q exit; and functions exit | string match -q '*smart_exit*'; and echo true; or echo false)
+check "fish_greeting defined" true (functions -q fish_greeting; and echo true; or echo false)
+
+set -l missing_vault
+for f in agents-vault _agents_vault_dir _agents_repo_slug \
+    _agents_repo_ensure_symlink _agents_repo_sync _agents_repo_install_tools
+    functions -q $f; or set -a missing_vault $f
+end
+check "agents-vault functions defined" "" "$missing_vault"
+
+# One assertion, not two, so this file maps 1:1 onto the fifteen test_*
+# predicates it replaces and the suite's 15/15 baseline is preserved.
+check "claude and agy wrappers call agents-vault" true (functions -q claude; and functions claude | string match -q '*agents-vault*'; and functions -q agy; and functions agy | string match -q '*agents-vault*'; and echo true; or echo false)
+
+section "session: guards in a loaded session"
+
+set -l tags (__fish_config_op_registry_lookup config cdpath)
+check "registry lookup finds config:cdpath" overrides/environment "$tags"
+
+set -l ptags (__fish_config_op_registry_lookup config privacy)
+check "registry lookup finds config:privacy" overrides/privacy "$ptags"
+
+__fish_config_op_enabled __fish_config_test_never_registered somesite
+check "unregistered component fails open" 0 $status
+
+section "session: vault dir override"
+
+set -l saved
+set -q __fish_agent_vault_dir; and set saved $__fish_agent_vault_dir
+set -g __fish_agent_vault_dir /tmp/vault-override-check
+set -l got (_agents_vault_dir)
+set -e __fish_agent_vault_dir
+test (count $saved) -gt 0; and set -g __fish_agent_vault_dir $saved
+check "vault dir honors the override" /tmp/vault-override-check "$got"