feat(config)!: one ordering for configuration sources, and a bootstrap deny rule

$DSH_HOME/.env had just become an ordinary environment layer, which left the
harness resolving user-facing values from a flattened process.env that could
no longer say where a value came from. A key stored through the web page
stayed shadowed by an older key in the user's own .env. An endpoint could be
redirected by the project: the invoking directory's .env is materialized like
every other layer, and a base URL decides where a resolved API key is sent, so
a DEEPSEEK_BASE_URL written into a model-editable workspace would send the
user's credential — and the prompts carrying their code — to whatever host
that file named.

Give every user-facing value one ordering, with four kinds of source:

  explicit for this run     per-operation override, CLI argument
  > authored by deployment  --config / --config-replace
  > this launch's shell     inherited process environment
  > product-managed store   settings.yaml, .credentials.yaml
  > discovered file         $DSH_HOME/.env
  > defaults                schema default, shipped base, public default

The domains differ only in which tiers exist. The earlier split — credentials
ranking the environment over the managed file while settings ranked over the
environment — was inconsistent: the distinguishing fact is who authored the
source, not the domain.

packages/util/environment owns an immutable snapshot with per-layer
provenance. getFrom(name, sources) searches only the layers a caller names,
and omitting one is a refusal rather than a demotion: the adapters ask for
['process', 'user-env'], so no reordering can let a project file back into a
decision it was excluded from.

isBootstrapOnly rejects, before anything is materialized, any .env setting a
variable that governs how a process launches (PATH, SHELL, NODE_OPTIONS,
LD_PRELOAD), where code or model-visible instructions load from (the whole
DSH_* namespace, HOME, XDG_*), or how the network is reached (proxy and CA
variables). The namespace is denied wholesale so a switch added later cannot
become settable by being forgotten, and there is no opt-out.

verify-config-source-ownership keeps both rules: no unregistered process.env
read under packages/*/*/src (26 allowlisted with reasons), and no apiKey,
baseURL, or headers inlined from the environment in shipped Cordis config —
removing those inlines is what makes the deployment tier meaningful.

apps/cli/tests/tui-keyless-smoke.e2e.ts

@@ -672,9 +672,9 @@ describe('dsh CLI keyless smoke (apps/cli through the same PTY)', () => {
     // layering underneath it. The named file patches the `tui` row — a row the
     // SURFACE OVERLAY inserted, not one the base declares — proving a later
     // patch list reaches a row an earlier one inserted. The `!!js` expression
-    // renders both halves of the layering in one line: `DSH_LAYER_WELCOME` is
+    // renders both halves of the layering in one line: `OVERLAY_LAYER_WELCOME` is
     // set by BOTH .env files and must render the project value, while
-    // `DSH_USER_ONLY` exists only in the harness home's .env and must still
+    // `OVERLAY_USER_ONLY` exists only in the harness home's .env and must still
     // arrive. Credentials are not part of this: they live in
     // `.credentials.yaml`, which is never hoisted into `process.env`.
     const output = await smoke({
@@ -683,17 +683,17 @@ describe('dsh CLI keyless smoke (apps/cli through the same PTY)', () => {
       binScript: dshBinScript,
       configArgs: ['--config', '.dsh/config.yaml'],
       prepare: seedWorkspace({
-        workspace: { '.env': 'DSH_LAYER_WELCOME=PROJECT WINS.\n' },
+        workspace: { '.env': 'OVERLAY_LAYER_WELCOME=PROJECT WINS.\n' },
         harnessHome: {
-          '.env': 'DSH_LAYER_WELCOME=USER LAYER LOST.\nDSH_USER_ONLY=USER LAYER LOADED.\n',
+          '.env': 'OVERLAY_LAYER_WELCOME=USER LAYER LOST.\nOVERLAY_USER_ONLY=USER LAYER LOADED.\n',
           'config.yaml': [
             '- id: workspace-context',
             '  disabled: true',
             '- id: tui',
             '  config:',
             "    sessionId: !!js configuredAgentIdentities?.main?.id ?? 'main'",
-            '    welcome: !!js "(process.env.DSH_LAYER_WELCOME ?? \'PROJECT LAYER MISSING.\')'
-            + ' + \' \' + (process.env.DSH_USER_ONLY ?? \'USER LAYER MISSING.\')"',
+            '    welcome: !!js "(process.env.OVERLAY_LAYER_WELCOME ?? \'PROJECT LAYER MISSING.\')'
+            + ' + \' \' + (process.env.OVERLAY_USER_ONLY ?? \'USER LAYER MISSING.\')"',
             '',
           ].join('\n'),
         },