diff --git a/COHERENCE.md b/COHERENCE.md
index 1594b69..954e621 100644
--- a/COHERENCE.md
+++ b/COHERENCE.md
@@ -120,9 +120,8 @@ asymmetry**, and **per-arc coherence debt**.
 
 Coherence-shaped work already in flight at audit time: find-file /
 dired Stage 0 (`C-x C-f`, PR #162, `docs/dired-framing.md`), bottom
-panel Stage 1 (merged #155), multi-root LSP affinity (branch
-`lsp-multi-root-affinity`), the config registry foundation (merged
-#127).
+panel Stage 1 (merged #155), multi-root LSP affinity (PR #161), the
+config registry foundation (merged #127).
 
 ---
 
@@ -230,9 +229,37 @@ This directly contradicts the product thesis (§23): the "without
 freezing" half is delivered; the "without becoming opaque" half is
 currently false for exactly the failures a new user will hit first.
 
+**The reporting channel the runtime believes it has does not exist.**
+Fifteen call sites — `async.lua` (5), `syntax.lua` (4), and one each in
+`lsp.lua`, `mcp.lua`, `fs.lua`, `editops.lua`, `autosave.lua`, and
+`commands/default.lua` — report background failures through
+`pmacs.error`, each guarded as `if pmacs.error then pmacs.error(...)`.
+**`pmacs.error` is never defined in production** — the only assignment
+in the tree is a test stub (`src/editor.rs:9881`), and
+`type(pmacs.error)` is `nil` in a fresh `EditorState`. So every one of
+those fifteen reports is dead: the guard makes the silence look
+deliberate and keeps it from ever being noticed. `pmacs.errors` (plural,
+`builtin/runtime/compile.lua:45`) is an unrelated namespace and is not
+it. This is the silence asymmetry one level deeper than §1.2 first
+recorded — not "the failure isn't surfaced" but "the surface was
+written, guarded, and never built." Found while landing PR #161, which
+nearly added a sixteenth; that one reports via
+`pmacs.editor.set_status` (which exists) with the `pmacs.error` arm
+riding along for when the channel is built.
+
 **Rule to adopt:** anything that fails automatically must leave a
 user-visible trace with a named owner. A `pcall` around background
-wiring must log attributed failure, never discard it.
+wiring must log attributed failure, never discard it. Corollary from the
+above: report through a channel with a **test that observes it**, or the
+guard is indistinguishable from the silence it was meant to fix.
+
+**Frequency note (PR #161):** per-root server affinity means the
+preconfigured-but-missing-server failure now fires **once per project
+root** rather than once per language per session. The silence is
+unchanged in kind; it is strictly more frequent. Surfacing it stays
+Priority 1 work with its own framing — it is a user-visible product
+behavior (what message, where, with what guidance), not a substrate fix
+to smuggle into an affinity PR.
 
 ### 1.3 Ground truth: coherence debt compounds per-arc
 
@@ -726,12 +753,14 @@ per-subsystem conventions.**
   nil/`"."`. Nothing owns the set {roots, servers, terminals, tasks,
   layout} — which is why desktop-save under a daemon had nothing
   principled to attach to (Q#DS9, §2 step 12).
-- **First slice in flight**: the multi-root LSP server-affinity work
-  (branch `lsp-multi-root-affinity`) makes *(language, found-root)* the
-  server identity — the first time a root functions as an identity key
-  rather than a spawn parameter. Note it is again per-subsystem: LSP
-  learns roots; compile, search, index, and trust do not share the
-  object.
+- **First slice landed (PR #161)**: the multi-root LSP server-affinity
+  work makes *(language, found-root)* the server identity — the first
+  time a root functions as an identity key rather than a spawn
+  parameter. It also establishes the rule that a *fallback* root (the
+  file's own directory, when no marker was found) is deliberately **not**
+  an identity, so markerless files keep sharing one server per language.
+  Note it is again per-subsystem: LSP learns roots; compile, search,
+  index, and trust do not share the object.
 
 A workspace entity is a **model gap** (real arc), not wiring. It is also
 the prerequisite that keeps §8 (locations), §9 (task ownership), §11
diff --git a/builtin/runtime/lsp.lua b/builtin/runtime/lsp.lua
index 4181156..6021134 100644
--- a/builtin/runtime/lsp.lua
+++ b/builtin/runtime/lsp.lua
@@ -30,9 +30,13 @@ pmacs.lsp = pmacs.lsp or {}
 --   env           (table)   extra environment
 --   init_options  (table)   `initializationOptions`
 --   settings      (table)   answered to `workspace/configuration`
---   root          (string)  optional explicit project root; overrides
+--   root  (string|function) optional explicit project root; overrides
 --                           the `pmacs.project.detect` marker walk used
---                           to set `rootUri`/`cwd` (see project_root_for)
+--                           to set `rootUri`/`cwd`. A `function(path) ->
+--                           string|nil` is resolved per file and
+--                           memoized per directory; returning nil
+--                           declines and falls through to the marker
+--                           walk (see project_root_for)
 pmacs.lsp.config = pmacs.lsp.config or {}
 
 -- Default rust-analyzer config. Users replace any field from init.lua
@@ -507,34 +511,144 @@ end
 --      the rest of the editor uses, honoring set_search_boundary,
 --   3. the file's own directory (a lone file still gets a sane root
 --      rather than leaking the editor cwd).
--- This is single-root: it fixes which root the one per-language server
--- uses, NOT one-server-per-root scoping (still deferred post-v0.1).
+-- Returns `root, source`, where `source` is "config", "detected", or
+-- "fallback" — and nil alongside a nil root. The source matters because
+-- only the first two mean a root was actually *found*; `ensure_server`
+-- keys server affinity on those and treats the fallback as rootless.
+--
+-- `config[language].root` may be a `function(path) -> string|nil` as
+-- well as a plain string, for languages whose root rule the shared
+-- marker walk cannot express (an innermost-wins walk cannot find an
+-- *outermost* marker). A resolver that returns nil declines, and
+-- resolution falls through to the marker walk.
+--
+-- **A configured root — string or resolver return — MUST be a canonical
+-- absolute path.** The `"detected"` arm is canonicalized for free
+-- (`pmacs.project.detect` canonicalizes before walking), but a
+-- configured one is fed to `file_uri_for` exactly as written, and the
+-- affinity key is that URI. On macOS a resolver returning `/var/…` and
+-- a detected `/private/var/…` are different keys for the same
+-- directory, which silently yields two servers for one project. There
+-- is no Lua-side canonicalizer to normalize this for you.
+--
+-- Resolver results are memoized per directory, because `ensure_server`
+-- resolves the root on the *reuse* path as well as the spawn path — so
+-- an unmemoized filesystem-walking resolver would re-walk on every
+-- attach rather than once per project. The memo is keyed by the
+-- resolver function itself, weakly: replacing `config[lang].root`
+-- installs a new key and the old memo is collected, so a swapped
+-- resolver can never serve a root the previous one computed.
+local root_resolver_memo = setmetatable({}, { __mode = "k" })
+
+local function resolve_root_fn(language, resolver, path)
+  local dir = dir_of(path)
+  if not dir then return nil end
+  local memo = root_resolver_memo[resolver]
+  if not memo then
+    memo = {}
+    root_resolver_memo[resolver] = memo
+  end
+  local hit = memo[dir]
+  -- `false` is the memoized form of "this resolver declined"; nil means
+  -- "not yet asked", so the two must stay distinguishable.
+  if hit ~= nil then
+    return hit or nil
+  end
+  local ok, resolved = pcall(resolver, path)
+  -- COHERENCE §1.2: background wiring must not DISCARD a failure. A
+  -- resolver that raises, or that returns something other than a string
+  -- or nil, is a config bug — and the memo below would otherwise bury
+  -- it permanently for this directory, so it is never observed again.
+  -- Returning nil is the documented decline and stays silent.
+  local failure
+  if not ok then
+    failure = "raised: " .. tostring(resolved)
+  elseif resolved ~= nil and type(resolved) ~= "string" then
+    failure = "returned a " .. type(resolved) .. "; want string or nil"
+  end
+  if failure then
+    local msg = string.format(
+      "LSP: %s root resolver for %s %s", language, dir, failure)
+    -- Report on the channel that EXISTS. `pmacs.error` is referenced by
+    -- fifteen guarded call sites across the runtime and is defined
+    -- nowhere in production (only by a test stub in `src/editor.rs`), so
+    -- `if pmacs.error then ...` alone would be a sixteenth report that
+    -- never fires — the unwired-guard shape, not a fix for it. The
+    -- status line is what lsp.lua already uses for every other LSP
+    -- error. The `pmacs.error` arm rides along so this upgrades for free
+    -- if that channel is ever built.
+    --
+    -- Both reports are pcall'd: a broken reporting channel must not turn
+    -- a declined root into a failed attach.
+    pcall(pmacs.editor.set_status, msg)
+    if pmacs.error then pcall(pmacs.error, msg) end
+    resolved = nil
+  end
+  if type(resolved) ~= "string" then resolved = nil end
+  memo[dir] = resolved or false
+  return resolved
+end
+
 local function project_root_for(language, path)
   local cfg = pmacs.lsp.config[language]
-  if cfg and cfg.root then return cfg.root end
-  if not path then return nil end
+  local configured = cfg and cfg.root
+  -- Truthiness, not `~= nil`: `root = false` has always read as "unset",
+  -- and a `false` leaking through as a root would reach `file_uri_for`.
+  if configured and type(configured) ~= "function" then
+    return configured, "config"
+  end
+  if not path then return nil, nil end
+  if configured then
+    local resolved = resolve_root_fn(language, configured, path)
+    if resolved then return resolved, "config" end
+  end
   local ok, det = pcall(pmacs.project.detect, path)
-  if ok and det and det.root then return det.root end
-  return dir_of(path)
+  if ok and det and det.root then return det.root, "detected" end
+  return dir_of(path), "fallback"
 end
 
 local function ensure_server(language, path)
   local cfg = pmacs.lsp.config[language]
   if not cfg or not cfg.command then return nil end
-  -- Reuse an existing same-language server if one is up. Multi-root
-  -- scoping (one server per project root) ships post-v0.1, so the
-  -- first file that attaches a given language fixes that server's
-  -- root; later files of the same language reuse it regardless of
-  -- their own project (known, documented limitation).
+  -- Reuse an existing same-language server *serving the same root*.
+  -- One server per project root: `lake serve` is bound to one Lake
+  -- package and rust-analyzer/gopls to one workspace, so handing the
+  -- second project's files to the first project's server yields
+  -- unresolvable imports and empty diagnostics.
+  --
+  -- The affinity key is the root only when a root was actually FOUND
+  -- (config override or marker walk). `project_root_for` never returns
+  -- nil for a file that has a path — its last resort is the file's own
+  -- directory — so keying on the fallback would give every directory
+  -- of loose scratch files its own server, for every language: two
+  -- stray .py files in different directories would spawn two pyrights
+  -- where today they share one. The fallback therefore keys on nil.
+  --
+  -- Matching is on the spawned spec's `root_uri`, nil matching nil, so
+  -- the fallback spawn must pass `root_uri = nil` for the key and the
+  -- stored spec to agree. `cwd` still carries the directory and
+  -- `build_initialize` derives the identical `rootUri` from it when the
+  -- field is None (src/lsp.rs), so the initialize payload is unchanged
+  -- for that case — only what this loop matches on changes.
+  --
+  -- Consequence, deliberate: a server hand-spawned from `init.lua` with
+  -- only `cwd` set also reads back nil, so a root-bearing attach will
+  -- not adopt it. We cannot know which root it was meant to serve, and
+  -- guessing wrongly routes a project's files to the wrong server.
+  local root, source = project_root_for(language, path)
+  local key_uri = nil
+  if source == "config" or source == "detected" then
+    key_uri = file_uri_for(root)
+  end
   for _, info in ipairs(pmacs.lsp.list()) do
-    if info.language_id == language and info.state then
+    if info.language_id == language and info.state
+        and info.root_uri == key_uri then
       local kind = info.state.kind
       if kind ~= "crashed" and kind ~= "stopped" then
         return info.id
       end
     end
   end
-  local root = project_root_for(language, path)
   local ok, sid = pcall(pmacs.lsp.spawn, {
     label = "default-" .. language,
     language_id = language,
@@ -544,7 +658,7 @@ local function ensure_server(language, path)
     init_options = cfg.init_options,
     settings = cfg.settings,
     cwd = root,
-    root_uri = root and file_uri_for(root) or nil,
+    root_uri = key_uri,
   })
   if ok then return sid end
   return nil
diff --git a/docs/active-work.md b/docs/active-work.md
index 3141a24..9ff342d 100644
--- a/docs/active-work.md
+++ b/docs/active-work.md
@@ -58,26 +58,46 @@ If it does not, stop and repair the remote/fetch configuration.
 
 - Portable branch: `githubsucks/inline-math-slice`; worktree
   `../pmacs-math-slice`. **PR #158**, base `main`.
-- **Canonical `main` @ `8c86d34` merged into the lane** (2026-07-25),
-  28 commits behind at the time. Merged rather than rebased, per the
-  #135/#137 precedent: the PR is awaiting review rounds and a rebase
-  would break every review anchor. The only conflict was this ledger —
-  both sides' lanes were kept — and it was **pre-existing**, not
-  introduced by the dired (#164) or Lean 4 ledger commits; it already
-  conflicted against `main` @ `e745068`.
-- **Integration surface** (derived from `git diff <merge-base>..main`,
-  not from another PR's file list): `pmacs-gpu/src/main.rs` gained 72
-  lines on main from `e547a90` — the minimap all-blank-slab
-  divide-by-zero fix — and this lane rewrites large parts of the same
-  file. Git auto-merged it **textually**; a clean auto-merge is not
-  evidence the tree compiles (the folding-arc lesson), so the full gate
-  suite below is what actually discharges it.
-- **CI had never run on this branch** — zero workflow runs since the PR
-  opened on 2026-07-24, while every other open PR has a full 12-check
-  run. Not a fork and not a trigger-config issue (the workflow fires on
-  all `pull_request` events); cause unidentified. The integration push
-  is what gets it its first run, so treat that run as the branch's
-  first real CI evidence.
+- **Canonical `main` merged into the lane twice on 2026-07-25**, both
+  times merged rather than rebased, per the #135/#137 precedent: the PR
+  is awaiting review rounds and a rebase would break every review anchor.
+  - First at `8c86d34` (28 commits behind). The conflict was
+    **pre-existing**, not introduced by the dired (#164) or Lean 4
+    ledger commits; it already conflicted against `main` @ `e745068`.
+  - Then at `46a1b8f`, after Lean 4 Stage 2 (#161) landed while this
+    branch's CI was still running. Same single conflict, same shape,
+    same resolution.
+- **Both conflicts were this ledger and nothing else** — both sides'
+  lanes kept verbatim each time. That is the standing cost of a
+  long-lived PR here: every merge to `main` edits this file, so a branch
+  awaiting review re-conflicts on it and only on it. It is a docs
+  collision, never a code one, and it says nothing about integration
+  risk — do not read a `CONFLICTING` badge on this PR as a code signal
+  without checking which file `git merge-tree` names.
+- **First integration's surface** (derived from `git diff
+  <merge-base>..main`, not from another PR's file list):
+  `pmacs-gpu/src/main.rs` gained 72 lines on main from `e547a90` — the
+  minimap all-blank-slab divide-by-zero fix — and this lane rewrites
+  large parts of the same file. Git auto-merged it **textually**; a
+  clean auto-merge is not evidence the tree compiles (the folding-arc
+  lesson), so the full gate suite below is what actually discharges it.
+- **Second integration's surface is code-disjoint.** #161 touched
+  `COHERENCE.md`, `builtin/runtime/lsp.lua`, `src/lua_bindings/mod.rs`,
+  and a new `tests/lsp_multi_root_acceptance.rs`; intersecting that
+  against this lane's own changed-file set leaves exactly one entry,
+  `docs/active-work.md`. No source file is touched by both sides, so
+  this one carries none of the first integration's semantic risk.
+- **CI ran on this branch for the first time on 2026-07-25 and passed
+  all twelve** (Format, both Lints, GPU Render headless, all four Test
+  matrix jobs, M1/M4/M5/M6 gates) at `8b457de` — the first-integration
+  tip. Before that there were zero workflow runs since the PR opened on
+  2026-07-24, while every other open PR had a full run; not a fork and
+  not a trigger-config issue (the workflow fires on all `pull_request`
+  events), cause never identified. So the green run **validates the
+  first integration, including the `pmacs-gpu/src/main.rs` auto-merge,
+  on macOS and Linux both** — the platforms local gating could not
+  cover. The second integration is not yet CI-covered, but its surface
+  is the ledger alone.
 - Framing: `docs/inline-math-slice-framing.md` rev 3, approved after two
   review rounds; parent arc framing merged as #154.
 - State: parser, font bundle (GUST licence), MATH-table layout with the
@@ -124,10 +144,11 @@ If it does not, stop and repair the remote/fetch configuration.
   spacer draws its box whole at the first run's origin; the fit budget
   reads the bundled code face even under a custom `set_font` family
   (the draw anchors to the real shaped baseline either way).
-## Lean 4 lane (Arc 8) — Stage 1 IN REVIEW (PR #160)
+## Lean 4 lane (Arc 8) — Stage 1 MERGED; Stage 2 IN REVIEW (PR #161)
 
-- Portable branch: `githubsucks/lean4-stage1`, worked in the shared
-  checkout (no sibling worktree), based on `githubsucks/main` @ `e745068`.
+- Stage 1 **merged as #160** (`main` @ `0827dd1`, 2026-07-25, one review
+  round, all twelve checks green). Branch `githubsucks/lean4-stage1`
+  retained; it was worked in the shared checkout (no sibling worktree).
 - Approved framing: `docs/lean4-mode-framing.md` revision 4, committed as
   the branch's first commit (`a382965`) after three review rounds. **Seven
   stages**, 19 decisions (Q#LN1–19), 64 acceptance criteria. North star:
@@ -183,16 +204,79 @@ If it does not, stop and repair the remote/fetch configuration.
   152; **isolated-config workspace sweep 3,150 across 90 suites**;
   `git diff --check` clean. The sweep needs an isolated `XDG_CONFIG_HOME`
   for the reason recorded in the bottom-panel lane below.
-- **Stage 2 is multi-root LSP server affinity** — pure substrate, no Lean
-  content, and it changes `ensure_server`, which every LSP language
-  shares. It is sequenced next because Lean is the language that makes its
-  absence a correctness failure rather than an inconvenience. Two
-  corrections the framing already carries for it: `root` is computed at
-  `lsp.lua:537`, **after** the reuse loop, so the fix must hoist it; and
-  `project_root_for` never returns nil for a file with a path, so the
-  affinity key must be the root only when a root was actually *detected*,
-  or markerless scratch files fragment into one server per directory for
-  every language.
+### Stage 2 — multi-root LSP server affinity (Q#LN15)
+
+- Portable branch: `githubsucks/lsp-multi-root-affinity`, shared checkout,
+  based on `githubsucks/main` @ `0827dd1`. Named for the substrate, not
+  for Lean: **the diff contains no Lean content**, because `ensure_server`
+  is the one server-affinity function every LSP language shares and a
+  cross-cutting change to it must not be reviewable only as a Lean
+  feature.
+- Three files, no protocol change: `src/lua_bindings/mod.rs` (the
+  `lsp.list()` row builder gains `root_uri` + `cwd`),
+  `builtin/runtime/lsp.lua` (`project_root_for` returns `root, source`;
+  `ensure_server` hoists it above the reuse loop and matches on it),
+  `tests/lsp_multi_root_acceptance.rs` (9 tests, acceptance 13–21).
+- **The rule that keeps this from regressing every other language: the
+  affinity key is the root only when a root was actually FOUND.**
+  `project_root_for` never returns nil for a file with a path — its last
+  resort is the file's own directory — so a naive `(language_id, root)`
+  key gives every directory of loose scratch files its own server, for
+  every language. `source` is `"config" | "detected" | "fallback"` and
+  only the first two become a key.
+- **Wire-identical for the fallback case, and that is provable rather
+  than hoped.** Matching is on the spawned spec's `root_uri` (nil matching
+  nil), so the fallback spawn passes `root_uri = nil`; `cwd` still carries
+  the directory and `build_initialize` derives the identical `rootUri`
+  from `cwd` when the field is None, using a percent-encoder with the same
+  allowed set as Lua's `file_uri_for`. `build_initialize` (`src/lsp.rs`)
+  is the **only** reader of `spec.root_uri` in the tree.
+- Deliberate behavior change, asserted not discovered: a server
+  hand-spawned from `init.lua` with only `cwd` set also reads back nil, so
+  a root-bearing attach will not adopt it.
+- `config[language].root` may now be a `function(path) -> string|nil`,
+  memoized per directory — needed because the hoist puts root resolution
+  on every attach rather than every spawn. The memo is keyed **weakly by
+  the resolver function itself**, so replacing `config[lang].root` cannot
+  serve a root the previous resolver computed. This is Q#LN8's
+  generalization landing early; the Lean resolver that uses it is Stage 3.
+- Bite-verified three ways: 5/9 fail against the pre-change `lsp.lua`,
+  8/9 against the pre-change `mod.rs`, and — the one that matters most —
+  installing the naive always-key-on-root variant fails acceptance 20 and
+  21 exactly as Q#LN15 part 2 predicts. The four that survive the first
+  bite (13, 15, 16, 19) are the regression pins; passing on both sides is
+  their job.
+- Every fixture sets `pmacs.project.set_search_boundary` at its own
+  tempdir root. Without it the marker walk climbs to the filesystem root
+  and a stray `.git` above the temp directory turns the markerless cases
+  into detected ones — the assertions would still pass while testing
+  nothing.
+- **Found but not fixed here (pre-existing, own lane):** `ensure_server`
+  never forwards `cfg.restart` to `pmacs.lsp.spawn`, so a
+  `restart = "never"` in `pmacs.lsp.config[lang]` is silently dropped on
+  the auto-attach path. At least one existing test sets it believing it
+  takes effect. Out of scope for a PR whose acceptance 16 pins existing
+  attach behavior as unchanged.
+- **Review round 1 addressed.** The blocker was process, not design: the
+  test file was committed *before* `cargo fmt` ran, so the fix sat
+  uncommitted in the working tree and the branch as pushed failed the
+  first gate. The reported "fmt clean" described the worktree, not the
+  branch — gate results are only meaningful when run against the pushed
+  tree. Also added the two pins review asked for (a **string** `config
+  .root` as an affinity key — acc17 only covered the function form; and
+  `root = false` reading as unset), each bite-verified against exactly
+  the mutation it targets and neither against the other. And documented
+  the canonicalization obligation: the `"detected"` arm is canonicalized
+  for free, a **configured** root is not, so on macOS a resolver
+  returning `/var/…` and a detected `/private/var/…` are different keys
+  for one directory. Stage 3's Lean resolver is the first real consumer,
+  so the obligation is written at the point of use.
+- Verification on this branch: `cargo fmt --check` clean; strict
+  workspace Clippy clean; 1,826 default + 2,003 CRDT library tests;
+  multi-root 11/11; M4 121; statusline 7; completion popup 9; auto-pair
+  45; required GPU 155; **isolated-config workspace sweep 3,164 across 91
+  suites**; `git diff --check` clean. The sweep needs an isolated
+  `XDG_CONFIG_HOME` and `-- --skip basedpyright`.
 
 ## Dired lane — framing APPROVED; Stage 0 MERGED, Stage 1 next
 
diff --git a/src/lua_bindings/mod.rs b/src/lua_bindings/mod.rs
index 29e3b47..3a92520 100644
--- a/src/lua_bindings/mod.rs
+++ b/src/lua_bindings/mod.rs
@@ -9923,12 +9923,26 @@ pub fn install_lsp(
                 let ids: Vec<LspServerId> = mgr.ids().collect();
                 let out = lua.create_table_with_capacity(ids.len(), 0)?;
                 for (i, id) in ids.iter().enumerate() {
-                    let row = lua.create_table_with_capacity(0, 5)?;
+                    let row = lua.create_table_with_capacity(0, 7)?;
                     row.set("id", LspServerIdLua(*id))?;
                     if let Some(spec) = mgr.spec(*id) {
                         row.set("label", spec.label.as_str())?;
                         row.set("language_id", spec.language_id.as_str())?;
                         row.set("command", spec.command.as_str())?;
+                        // Server *affinity* fields. `root_uri` is the spec
+                        // field verbatim — deliberately NOT the URI the
+                        // server was initialized with, which `build_initialize`
+                        // derives from `cwd` when the field is `None`. Lua's
+                        // `ensure_server` matches on this exact value, so a
+                        // server that never asked for a specific root must
+                        // read back as nil rather than as its cwd; see the
+                        // affinity-key comment in `builtin/runtime/lsp.lua`.
+                        if let Some(root_uri) = spec.root_uri.as_deref() {
+                            row.set("root_uri", root_uri)?;
+                        }
+                        if let Some(cwd) = spec.cwd.as_deref() {
+                            row.set("cwd", cwd.display().to_string())?;
+                        }
                     }
                     if let Some(state) = mgr.state(*id) {
                         row.set("state", lsp_state_to_lua(lua, state)?)?;
diff --git a/tests/lsp_multi_root_acceptance.rs b/tests/lsp_multi_root_acceptance.rs
new file mode 100644
index 0000000..39ac68f
--- /dev/null
+++ b/tests/lsp_multi_root_acceptance.rs
@@ -0,0 +1,704 @@
+//! Arc 8 Stage 2 acceptance — multi-root LSP server affinity.
+//!
+//! `docs/lean4-mode-framing.md` Q#LN15, acceptance 13–21.
+//!
+//! This suite deliberately contains **no Lean content**. `ensure_server`
+//! (`builtin/runtime/lsp.lua`) is the single server-affinity function for
+//! every LSP language in pmacs, so the change is exercised through the
+//! four languages that already shipped attach paths — rust, python, go,
+//! typescript — driven against `pmacs_fake_lsp` so nothing here needs a
+//! real toolchain on PATH.
+//!
+//! Every fixture calls `pmacs.project.set_search_boundary` at its own
+//! tempdir root. Without it the marker walk climbs to the filesystem
+//! root, and a stray `.git` above the temp directory would silently turn
+//! the "markerless" cases into detected ones — the assertions would still
+//! pass while testing nothing.
+
+use std::path::{Path, PathBuf};
+use std::time::Duration;
+
+use pmacs::editor::EditorState;
+
+fn exec(state: &EditorState, source: &str) {
+    state.lua_host.lua().load(source.to_owned()).exec().unwrap();
+}
+
+fn eval<T: mlua::FromLuaMulti>(state: &EditorState, source: &str) -> T {
+    state.lua_host.lua().load(source.to_owned()).eval().unwrap()
+}
+
+fn fake_lsp_path() -> String {
+    env!("CARGO_BIN_EXE_pmacs_fake_lsp").to_owned()
+}
+
+/// A fresh editor with the shipped language configs cleared, so the only
+/// server any test can spawn is the fake one it configures itself.
+fn editor() -> EditorState {
+    let state = EditorState::new();
+    exec(&state, "pmacs.lsp.config = {}");
+    state
+}
+
+fn lua_str(path: &Path) -> String {
+    path.display()
+        .to_string()
+        .replace('\\', "\\\\")
+        .replace('"', "\\\"")
+}
+
+/// Mirror of `file_uri_for` in `builtin/runtime/lsp.lua` and
+/// `path_to_file_uri` in `src/lsp.rs`. Reimplemented rather than
+/// imported so the test states the expected encoding independently of
+/// the code under test.
+fn file_uri(path: &Path) -> String {
+    let mut out = String::from("file://");
+    for ch in path.display().to_string().chars() {
+        match ch {
+            'a'..='z' | 'A'..='Z' | '0'..='9' | '/' | '-' | '_' | '.' | '~' | ':' => out.push(ch),
+            _ => {
+                use std::fmt::Write as _;
+                let mut buf = [0u8; 4];
+                for byte in ch.encode_utf8(&mut buf).as_bytes() {
+                    let _ = write!(out, "%{byte:02X}");
+                }
+            }
+        }
+    }
+    out
+}
+
+struct Fixture {
+    _dir: tempfile::TempDir,
+    root: PathBuf,
+}
+
+impl Fixture {
+    /// Canonicalized so the expected roots below compare equal to what
+    /// `pmacs.project.detect` returns (it canonicalizes before walking,
+    /// which matters on macOS where `/var` is a symlink to `/private/var`).
+    fn new() -> Self {
+        let dir = tempfile::tempdir().unwrap();
+        let root = std::fs::canonicalize(dir.path()).unwrap();
+        Self { _dir: dir, root }
+    }
+
+    fn write(&self, rel: &str, contents: &str) -> PathBuf {
+        let path = self.root.join(rel);
+        std::fs::create_dir_all(path.parent().unwrap()).unwrap();
+        std::fs::write(&path, contents).unwrap();
+        path
+    }
+
+    fn dir(&self, rel: &str) -> PathBuf {
+        self.root.join(rel)
+    }
+
+    fn bind(&self, state: &EditorState) {
+        exec(
+            state,
+            &format!(
+                "pmacs.project.set_search_boundary(\"{}\")",
+                lua_str(&self.root)
+            ),
+        );
+    }
+}
+
+fn configure(state: &EditorState, language: &str) {
+    exec(
+        state,
+        &format!(
+            "pmacs.lsp.config.{language} = {{ command = \"{}\" }}",
+            fake_lsp_path()
+        ),
+    );
+}
+
+fn open(state: &EditorState, path: &Path) {
+    exec(
+        state,
+        &format!("pmacs.buffer.find_or_open(\"{}\")", lua_str(path)),
+    );
+}
+
+fn settle(state: &mut EditorState) {
+    for _ in 0..8 {
+        state.tick_processes();
+        state.tick_lsp();
+        std::thread::sleep(Duration::from_millis(2));
+    }
+}
+
+/// One `language_id|root_uri|cwd|state` row per live server, sorted so
+/// assertions do not depend on spawn order. Absent fields read as "".
+fn rows(state: &EditorState) -> Vec<String> {
+    let joined: String = eval(
+        state,
+        r#"
+        local out = {}
+        for _, s in ipairs(pmacs.lsp.list()) do
+          out[#out + 1] = table.concat({
+            s.language_id or "",
+            s.root_uri or "",
+            s.cwd or "",
+            (s.state and s.state.kind) or "",
+          }, "|")
+        end
+        table.sort(out)
+        return table.concat(out, "\n")
+        "#,
+    );
+    if joined.is_empty() {
+        Vec::new()
+    } else {
+        joined.lines().map(str::to_owned).collect()
+    }
+}
+
+fn status(state: &EditorState) -> String {
+    state.core.borrow().status.clone()
+}
+
+fn count(state: &EditorState) -> usize {
+    let n: i64 = eval(state, "return #pmacs.lsp.list()");
+    usize::try_from(n).expect("server count is non-negative")
+}
+
+// ---------------------------------------------------------------------------
+// Acceptance 13 — `lsp.list()` rows carry `root_uri` and `cwd`.
+// ---------------------------------------------------------------------------
+
+#[test]
+fn acc13_list_rows_carry_root_uri_and_cwd() {
+    let fx = Fixture::new();
+    fx.write("proj/Cargo.toml", "[package]\nname = \"p\"\n");
+    let file = fx.write("proj/src/main.rs", "fn main() {}\n");
+    let mut state = editor();
+    fx.bind(&state);
+    configure(&state, "rust");
+    open(&state, &file);
+    settle(&mut state);
+
+    let proj = fx.dir("proj");
+    let rows = rows(&state);
+    assert_eq!(rows.len(), 1, "{rows:?}");
+    let fields: Vec<&str> = rows[0].split('|').collect();
+    assert_eq!(fields[0], "rust");
+    assert_eq!(
+        fields[1],
+        file_uri(&proj),
+        "root_uri must be the project root"
+    );
+    assert_eq!(
+        fields[2],
+        proj.display().to_string(),
+        "cwd must be the root"
+    );
+}
+
+// ---------------------------------------------------------------------------
+// Acceptance 14 — two roots, same language, two servers.
+// ---------------------------------------------------------------------------
+
+#[test]
+fn acc14_two_project_roots_of_one_language_spawn_two_servers() {
+    let fx = Fixture::new();
+    fx.write("a/Cargo.toml", "[package]\nname = \"a\"\n");
+    fx.write("b/Cargo.toml", "[package]\nname = \"b\"\n");
+    let first = fx.write("a/src/main.rs", "fn main() {}\n");
+    let second = fx.write("b/src/main.rs", "fn main() {}\n");
+    let mut state = editor();
+    fx.bind(&state);
+    configure(&state, "rust");
+    open(&state, &first);
+    settle(&mut state);
+    open(&state, &second);
+    settle(&mut state);
+
+    let rows = rows(&state);
+    assert_eq!(rows.len(), 2, "one server per project root: {rows:?}");
+    let roots: Vec<&str> = rows.iter().map(|r| r.split('|').nth(1).unwrap()).collect();
+    assert!(
+        roots.contains(&file_uri(&fx.dir("a")).as_str()),
+        "{roots:?}"
+    );
+    assert!(
+        roots.contains(&file_uri(&fx.dir("b")).as_str()),
+        "{roots:?}"
+    );
+}
+
+// ---------------------------------------------------------------------------
+// Acceptance 15 — same root, two files, one server. The pre-change
+// behavior, pinned so the fix cannot degrade into "always spawn".
+// ---------------------------------------------------------------------------
+
+#[test]
+fn acc15_two_files_in_one_root_reuse_a_single_server() {
+    let fx = Fixture::new();
+    fx.write("proj/Cargo.toml", "[package]\nname = \"p\"\n");
+    let first = fx.write("proj/src/main.rs", "fn main() {}\n");
+    let second = fx.write("proj/src/other.rs", "pub fn other() {}\n");
+    let mut state = editor();
+    fx.bind(&state);
+    configure(&state, "rust");
+    open(&state, &first);
+    settle(&mut state);
+    open(&state, &second);
+    settle(&mut state);
+
+    let rows = rows(&state);
+    assert_eq!(rows.len(), 1, "same root must reuse: {rows:?}");
+    assert_eq!(
+        rows[0].split('|').nth(1).unwrap(),
+        file_uri(&fx.dir("proj"))
+    );
+}
+
+// ---------------------------------------------------------------------------
+// Acceptance 16 — per-language regression pin. The single-root case is
+// all the shipped attach paths ever exercised; it must be untouched.
+// ---------------------------------------------------------------------------
+
+#[test]
+fn acc16_shipped_languages_are_unchanged_for_the_single_root_case() {
+    // (language id, project marker, two source files under it)
+    let cases: [(&str, &str, &str, &str); 4] = [
+        ("rust", "Cargo.toml", "one.rs", "two.rs"),
+        ("python", "pyproject.toml", "one.py", "two.py"),
+        ("go", "go.mod", "one.go", "two.go"),
+        ("typescript", "package.json", "one.ts", "two.ts"),
+    ];
+    for (language, marker, first_name, second_name) in cases {
+        let fx = Fixture::new();
+        fx.write(&format!("proj/{marker}"), "{}\n");
+        let first = fx.write(&format!("proj/src/{first_name}"), "\n");
+        let second = fx.write(&format!("proj/src/{second_name}"), "\n");
+        let mut state = editor();
+        fx.bind(&state);
+        configure(&state, language);
+        open(&state, &first);
+        settle(&mut state);
+        open(&state, &second);
+        settle(&mut state);
+
+        let rows = rows(&state);
+        assert_eq!(
+            rows.len(),
+            1,
+            "{language}: expected one server, got {rows:?}"
+        );
+        let fields: Vec<&str> = rows[0].split('|').collect();
+        assert_eq!(fields[0], language, "{language}: language_id");
+        assert_eq!(
+            fields[1],
+            file_uri(&fx.dir("proj")),
+            "{language}: root must be the marker directory"
+        );
+    }
+}
+
+// ---------------------------------------------------------------------------
+// Acceptance 17 — hoist pin. `project_root_for` now runs on the *reuse*
+// path, and a function-valued `root` is memoized per directory.
+// ---------------------------------------------------------------------------
+
+#[test]
+fn acc17_function_root_runs_on_the_reuse_path_and_memoizes_per_directory() {
+    let fx = Fixture::new();
+    let shared = fx.dir("shared");
+    std::fs::create_dir_all(&shared).unwrap();
+    let a1 = fx.write("one/a.rs", "fn a() {}\n");
+    let a2 = fx.write("one/b.rs", "fn b() {}\n");
+    let b1 = fx.write("two/c.rs", "fn c() {}\n");
+    let mut state = editor();
+    fx.bind(&state);
+    // A resolver that answers the same root for every directory: the
+    // second directory therefore REUSES the first directory's server,
+    // which is exactly the path the hoist put the resolver on.
+    exec(
+        &state,
+        &format!(
+            r#"
+            _G.ROOT_CALLS = 0
+            pmacs.lsp.config.rust = {{
+              command = "{}",
+              root = function(_)
+                _G.ROOT_CALLS = _G.ROOT_CALLS + 1
+                return "{}"
+              end,
+            }}
+            "#,
+            fake_lsp_path(),
+            lua_str(&shared)
+        ),
+    );
+
+    open(&state, &a1);
+    settle(&mut state);
+    assert_eq!(eval::<i64>(&state, "return _G.ROOT_CALLS"), 1, "spawn path");
+
+    // Same directory: served from the memo, so the count does not move.
+    open(&state, &a2);
+    settle(&mut state);
+    assert_eq!(
+        eval::<i64>(&state, "return _G.ROOT_CALLS"),
+        1,
+        "second file in the same directory must hit the memo"
+    );
+
+    // Different directory: the resolver runs again — proving the reuse
+    // path resolves at all — but resolves to the same root, so no second
+    // server appears.
+    open(&state, &b1);
+    settle(&mut state);
+    assert_eq!(
+        eval::<i64>(&state, "return _G.ROOT_CALLS"),
+        2,
+        "a new directory must consult the resolver on the reuse path"
+    );
+    let rows = rows(&state);
+    assert_eq!(rows.len(), 1, "one resolved root, one server: {rows:?}");
+    assert_eq!(rows[0].split('|').nth(1).unwrap(), file_uri(&shared));
+}
+
+// ---------------------------------------------------------------------------
+// Acceptance 18 — a hand-spawned server carrying only `cwd` is not
+// adopted by a root-bearing attach. A deliberate behavior change.
+// ---------------------------------------------------------------------------
+
+#[test]
+fn acc18_hand_spawned_server_without_root_uri_is_not_adopted() {
+    let fx = Fixture::new();
+    fx.write("proj/Cargo.toml", "[package]\nname = \"p\"\n");
+    let file = fx.write("proj/src/main.rs", "fn main() {}\n");
+    let proj = fx.dir("proj");
+    let mut state = editor();
+    fx.bind(&state);
+    configure(&state, "rust");
+    // Exactly what an init.lua would write: cwd, no root_uri.
+    exec(
+        &state,
+        &format!(
+            r#"
+            pmacs.lsp.spawn({{
+              label = "hand-rolled",
+              language_id = "rust",
+              command = "{}",
+              cwd = "{}",
+            }})
+            "#,
+            fake_lsp_path(),
+            lua_str(&proj)
+        ),
+    );
+    settle(&mut state);
+    assert_eq!(count(&state), 1, "the hand-spawned server is up");
+
+    open(&state, &file);
+    settle(&mut state);
+
+    let rows = rows(&state);
+    assert_eq!(rows.len(), 2, "the attach must not adopt it: {rows:?}");
+    let roots: Vec<&str> = rows.iter().map(|r| r.split('|').nth(1).unwrap()).collect();
+    assert!(
+        roots.contains(&""),
+        "hand-spawned reads back nil: {roots:?}"
+    );
+    assert!(
+        roots.contains(&file_uri(&proj).as_str()),
+        "the attach's own server carries the root: {roots:?}"
+    );
+}
+
+// ---------------------------------------------------------------------------
+// Acceptance 19 — a dead server in the matching root is not reused.
+// ---------------------------------------------------------------------------
+
+#[test]
+fn acc19_stopped_server_in_the_matching_root_is_not_reused() {
+    let fx = Fixture::new();
+    fx.write("proj/Cargo.toml", "[package]\nname = \"p\"\n");
+    let first = fx.write("proj/src/main.rs", "fn main() {}\n");
+    let second = fx.write("proj/src/other.rs", "pub fn other() {}\n");
+    let mut state = editor();
+    fx.bind(&state);
+    configure(&state, "rust");
+    open(&state, &first);
+    settle(&mut state);
+    let original: i64 = eval(&state, "return pmacs.lsp.list()[1].id:raw()");
+
+    exec(&state, "pmacs.lsp.stop(pmacs.lsp.list()[1].id)");
+    for _ in 0..200 {
+        settle(&mut state);
+        let dead: bool = eval(
+            &state,
+            r#"
+            for _, s in ipairs(pmacs.lsp.list()) do
+              local k = s.state and s.state.kind
+              if k == "stopped" or k == "crashed" then return true end
+            end
+            return false
+            "#,
+        );
+        if dead {
+            break;
+        }
+    }
+
+    open(&state, &second);
+    settle(&mut state);
+    let live: i64 = eval(
+        &state,
+        r#"
+        for _, s in ipairs(pmacs.lsp.list()) do
+          local k = s.state and s.state.kind
+          if k ~= "stopped" and k ~= "crashed" then
+            return s.id:raw()
+          end
+        end
+        return -1
+        "#,
+    );
+    assert_ne!(live, -1, "a replacement server must exist");
+    assert_ne!(live, original, "the dead server must not be reused");
+}
+
+// ---------------------------------------------------------------------------
+// Acceptance 20 — the loose-file pin (Q#LN15 part 2). This is the
+// no-change case, and the one a naive `(language_id, root)` key breaks.
+// ---------------------------------------------------------------------------
+
+#[test]
+fn acc20_markerless_files_in_different_directories_share_one_server() {
+    let fx = Fixture::new();
+    let first = fx.write("loose_a/one.rs", "fn one() {}\n");
+    let second = fx.write("loose_b/two.rs", "fn two() {}\n");
+    let mut state = editor();
+    fx.bind(&state);
+    configure(&state, "rust");
+    open(&state, &first);
+    settle(&mut state);
+    open(&state, &second);
+    settle(&mut state);
+
+    let rows = rows(&state);
+    assert_eq!(
+        rows.len(),
+        1,
+        "loose files must keep sharing one server: {rows:?}"
+    );
+    let fields: Vec<&str> = rows[0].split('|').collect();
+    assert_eq!(fields[1], "", "the fallback root is not an affinity key");
+    assert_eq!(
+        fields[2],
+        fx.dir("loose_a").display().to_string(),
+        "cwd still carries the first file's directory"
+    );
+}
+
+// ---------------------------------------------------------------------------
+// Acceptance 21 — detected and fallback are different servers, and the
+// fallback one still carries its directory as `cwd`.
+// ---------------------------------------------------------------------------
+
+#[test]
+fn acc21_detected_root_and_markerless_file_get_different_servers() {
+    let fx = Fixture::new();
+    fx.write("proj/Cargo.toml", "[package]\nname = \"p\"\n");
+    let inside = fx.write("proj/src/main.rs", "fn main() {}\n");
+    let loose = fx.write("loose/stray.rs", "fn stray() {}\n");
+    let mut state = editor();
+    fx.bind(&state);
+    configure(&state, "rust");
+    open(&state, &inside);
+    settle(&mut state);
+    open(&state, &loose);
+    settle(&mut state);
+
+    let rows = rows(&state);
+    assert_eq!(rows.len(), 2, "detected and fallback must differ: {rows:?}");
+    let detected = rows
+        .iter()
+        .find(|r| r.split('|').nth(1).unwrap() == file_uri(&fx.dir("proj")))
+        .unwrap_or_else(|| panic!("no server rooted at the project: {rows:?}"));
+    assert_eq!(
+        detected.split('|').nth(2).unwrap(),
+        fx.dir("proj").display().to_string()
+    );
+    let fallback = rows
+        .iter()
+        .find(|r| r.split('|').nth(1).unwrap().is_empty())
+        .unwrap_or_else(|| panic!("no rootless server: {rows:?}"));
+    assert_eq!(
+        fallback.split('|').nth(2).unwrap(),
+        fx.dir("loose").display().to_string(),
+        "the markerless server keeps the fallback directory as cwd"
+    );
+}
+
+// ---------------------------------------------------------------------------
+// Review-round-1 pins. Neither is a numbered acceptance criterion; both
+// cover a branch the nine above leave untested.
+// ---------------------------------------------------------------------------
+
+/// A *string* `config.root` is an affinity key. acc17 covers the function
+/// form; without this the `return configured, "config"` arm has no test.
+///
+/// The bite: both files sit in their own marked project, so if the config
+/// arm were dropped they would key on their own detected roots and spawn
+/// two servers. One server keyed on the configured root is only possible
+/// if the override wins.
+#[test]
+fn config_string_root_overrides_detection_as_the_affinity_key() {
+    let fx = Fixture::new();
+    fx.write("a/Cargo.toml", "[package]\nname = \"a\"\n");
+    fx.write("b/Cargo.toml", "[package]\nname = \"b\"\n");
+    let first = fx.write("a/src/main.rs", "fn main() {}\n");
+    let second = fx.write("b/src/main.rs", "fn main() {}\n");
+    let shared = fx.dir("shared");
+    std::fs::create_dir_all(&shared).unwrap();
+    let mut state = editor();
+    fx.bind(&state);
+    exec(
+        &state,
+        &format!(
+            "pmacs.lsp.config.rust = {{ command = \"{}\", root = \"{}\" }}",
+            fake_lsp_path(),
+            lua_str(&shared)
+        ),
+    );
+    open(&state, &first);
+    settle(&mut state);
+    open(&state, &second);
+    settle(&mut state);
+
+    let rows = rows(&state);
+    assert_eq!(
+        rows.len(),
+        1,
+        "a configured root outranks both detected roots: {rows:?}"
+    );
+    let fields: Vec<&str> = rows[0].split('|').collect();
+    assert_eq!(fields[1], file_uri(&shared), "keyed on the configured root");
+    assert_eq!(fields[2], shared.display().to_string());
+}
+
+/// `root = false` reads as unset, as it always has. Defended in
+/// `project_root_for` by a truthiness check rather than `~= nil`; this
+/// pins the behavior instead of trusting the comment.
+///
+/// The bite: under a `~= nil` test the config arm would return
+/// `false, "config"`, and `file_uri_for(false)` returns nil — so the file
+/// would land on a rootless server instead of its detected project.
+#[test]
+fn config_root_false_reads_as_unset_and_detection_still_wins() {
+    let fx = Fixture::new();
+    fx.write("proj/Cargo.toml", "[package]\nname = \"p\"\n");
+    let file = fx.write("proj/src/main.rs", "fn main() {}\n");
+    let mut state = editor();
+    fx.bind(&state);
+    exec(
+        &state,
+        &format!(
+            "pmacs.lsp.config.rust = {{ command = \"{}\", root = false }}",
+            fake_lsp_path()
+        ),
+    );
+    open(&state, &file);
+    settle(&mut state);
+
+    let rows = rows(&state);
+    assert_eq!(rows.len(), 1, "{rows:?}");
+    assert_eq!(
+        rows[0].split('|').nth(1).unwrap(),
+        file_uri(&fx.dir("proj")),
+        "`false` must not become a root; detection still wins"
+    );
+}
+
+/// COHERENCE §1.2: background wiring must leave an attributed trace
+/// rather than discard a failure. A throwing root resolver is a config
+/// bug, and the per-directory memo would otherwise bury it permanently.
+///
+/// The bite: drop the reporting arm and `*errors*` stays empty while the
+/// attach still succeeds — the exact silence §1.2 names as the canonical
+/// anti-pattern, in the function it cites.
+#[test]
+fn a_throwing_root_resolver_leaves_an_attributed_trace() {
+    let fx = Fixture::new();
+    fx.write("proj/Cargo.toml", "[package]\nname = \"p\"\n");
+    let file = fx.write("proj/src/main.rs", "fn main() {}\n");
+    let mut state = editor();
+    fx.bind(&state);
+    exec(
+        &state,
+        &format!(
+            r#"
+            pmacs.lsp.config.rust = {{
+              command = "{}",
+              root = function(_) error("resolver blew up") end,
+            }}
+            "#,
+            fake_lsp_path()
+        ),
+    );
+    open(&state, &file);
+    settle(&mut state);
+
+    let msg = status(&state);
+    assert!(
+        msg.contains("root resolver"),
+        "a raising resolver must leave an attributed trace; got: {msg:?}"
+    );
+    assert!(
+        msg.contains("rust"),
+        "the trace must name the language that owns it; got: {msg:?}"
+    );
+    assert!(
+        msg.contains("resolver blew up"),
+        "the underlying error text must survive; got: {msg:?}"
+    );
+
+    // ...and the failure must degrade to a decline, not a failed attach:
+    // detection still wins and the buffer still gets its server.
+    let rows = rows(&state);
+    assert_eq!(rows.len(), 1, "the attach must still succeed: {rows:?}");
+    assert_eq!(
+        rows[0].split('|').nth(1).unwrap(),
+        file_uri(&fx.dir("proj")),
+        "a declining resolver falls through to the marker walk"
+    );
+}
+
+/// The decline path stays silent. Without this, "report failures" could
+/// be satisfied by reporting *every* resolution, which would spam
+/// `*errors*` on every attach in a Lean project.
+#[test]
+fn a_resolver_returning_nil_declines_silently() {
+    let fx = Fixture::new();
+    fx.write("proj/Cargo.toml", "[package]\nname = \"p\"\n");
+    let file = fx.write("proj/src/main.rs", "fn main() {}\n");
+    let mut state = editor();
+    fx.bind(&state);
+    exec(
+        &state,
+        &format!(
+            "pmacs.lsp.config.rust = {{ command = \"{}\", root = function(_) return nil end }}",
+            fake_lsp_path()
+        ),
+    );
+    open(&state, &file);
+    settle(&mut state);
+
+    let msg = status(&state);
+    assert!(
+        !msg.contains("root resolver"),
+        "returning nil is the documented decline, not a failure; got: {msg:?}"
+    );
+    assert_eq!(
+        rows(&state)[0].split('|').nth(1).unwrap(),
+        file_uri(&fx.dir("proj"))
+    );
+}