fix: stop the facet preset naming a prompt variable the harness dropped

The preset's persona row copied the deployment's suffix, "Your working directory
is {{cwd}}". The harness substitutes only registered prompt variables and throws
on an unregistered one during prompt assembly — so when a harness release stopped
registering `cwd` (only `provider` and `model` remain), every session on this
preset failed its first turn with

  unknown prompt variable "{{cwd}}" in section "deployment:persona-suffix"

and chat was dead rather than degraded. The row now carries the prefix only.

The folder is stated where it can follow the session instead: the facet binding
already names the facet, and now names the session folder as well when the two
differ — which is every conversation that started higher up and was narrowed, and
exactly the case where relative tool paths need saying out loud.

`test/presets.test.js` makes this class of failure impossible to reintroduce
silently: it scans every shipped preset for a variable reference and requires the
name to be one the harness registers, and holds this bundle's own rule and
binding text to no references at all. Restoring the old suffix fails it.

README.md

@@ -237,6 +237,27 @@ replaces the whole plugin list rather than merging into it, so the file is a
 frozen copy of `standard` that will not follow the harness when `standard`
 changes.
 
+### Prompt variables, and why the preset's persona has no suffix
+
+Both preset files used to copy the deployment's persona line, *Your working
+directory is {{cwd}}*. The harness registers prompt variables per section and an
+unregistered reference **throws during prompt assembly**, which fails the entire
+turn — not a warning, not a literal left in the text. That is not a hypothetical:
+a harness release stopped registering `cwd` (only `provider` and `model` remain),
+and every session on this bundle's preset failed with
+`unknown prompt variable "{{cwd}}" in section "deployment:persona-suffix"`.
+
+So neither preset carries that suffix now, and the folder is stated where it can
+follow the session instead: `facet-guard`'s runtime binding names the facet, and
+names the session folder too when the two differ — which is exactly the case
+where relative tool paths need saying out loud. `test/presets.test.js` scans both
+files for `{{…}}` and fails on any name outside `provider, model`, and the same
+test holds this bundle's own rule and binding text to no references at all.
+
+If a *deployment* still fails with that message on a non-facet preset, the
+reference is in the deployment's own `system-prompt` config (`personaSuffix`) or
+in a copy of the shipped `standard` patch, not in this bundle.
+
 ## What it does not cover
 
 Honest boundaries, because each one is a decision rather than an oversight:
@@ -264,7 +285,7 @@ Honest boundaries, because each one is a decision rather than an oversight:
 
 Verified:
 
-- 93 tests (`npm test`) over the scope algebra, the policy state, the guard, and
+- 95 tests (`npm test`) over the scope algebra, the policy state, the guard, and
   the browser half — including that containment is decided on canonical targets
   (a symlink inside the facet pointing outside it is refused), that a prefix is
   not a parent (`/a/room` does not contain `/a/roommate`), that a malformed tool
@@ -275,8 +296,10 @@ Verified:
   is refused when the directory it defaults to is outside the facet, that a
   delegated session inherits its parent's root at any depth and is not a way back
   out of a self-narrowing, that both listings normalise into one picker level and
-  that a file listing the Host confines still leaves a browsable one, and that
-  every `facet` result satisfies the tool's own declared output schema.
+  that a file listing the Host confines still leaves a browsable one, that no
+  preset or contributed prompt text references a prompt variable the harness
+  does not register, and that every `facet` result satisfies the tool's own
+  declared output schema.
 - The bundle's patch layers parse, merge and land correctly against the real
   profile: `dsh --profile web --patch ./cordis.patch.yml --patch
   ./presets/facet.patch.yml --dump-config` shows `facet-policy`, `preset-facet`,
@@ -354,7 +377,7 @@ lib/scope.js                 the pure half — argument extraction, text, reason
 lib/guard.js                 preset row: rule, binding, tool, pre-execute guard
 presets/facet.patch.yml      the `facet` agent preset
 presets/standard-compaction.patch.yml   optional: the same budget for `standard`
-test/                        93 tests
+test/                        95 tests
 ```
 
 `client/client.js` is a browser half rather than a module the host imports, and