Instruction files stack from the project root down to the working directory

instructionChain (spec 3.0.0, filesystem.md): from the boundary — the project
root — down to the start directory, outermost first, each directory gives the
first of AGENTS.md, CLAUDE.md that is a file really inside the project; one
that is not (a link out) is passed over and the walk goes on below it. Before,
only the nearest file counted. The chain's files are named to the model by
their path in the project; agentsBlock reads them all: none means "make one",
and git is settled when any of them settles it.

Conformance runner for the `instructions` area (all 9 cases pass).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/conformance.ts

@@ -18,11 +18,24 @@ import { parseInfo, titleFor } from "../src/prototype/fence.ts"
 import { resolveBase } from "../src/library/store.ts"
 import { NarrowError, narrowParameters, type Narrow } from "../src/harness.ts"
 import { fillPrompt } from "../src/prompt/fill.ts"
+import { instructionChain } from "../src/prompt/assemble.ts"
 import { applyOps, type Op, type Target } from "../src/memory/store.ts"
 import { jobNote, type NoteCase } from "../src/jobs/note.ts"
 
 type Case = Record<string, unknown>
 
+/** Whether a path is at `ro` or above under `grants` (fs_access's rule: the most specific grant on
+ *  the path or above it wins; none where nothing is granted). No grants at all: everything readable. */
+function readableUnder(grants: Record<string, string> | undefined, path: string): boolean {
+  if (!grants) return true
+  let best: string | undefined
+  for (const g of Object.keys(grants)) {
+    const covers = g === "/" || path === g || path.startsWith(g + "/")
+    if (covers && (best === undefined || g.length > best.length)) best = g
+  }
+  return best !== undefined && grants[best] !== "none"
+}
+
 export const AREAS: Record<string, (c: Case) => unknown> = {
   hardline: (c) => hardlineCommand(c.line as string, BUILTIN_HARDLINE)?.id ?? null,
   split: (c) => splitCommand(c.line as string),
@@ -96,6 +109,12 @@ export const AREAS: Record<string, (c: Case) => unknown> = {
     return { ok: r.ok, entries: r.ok ? r.after : c.entries, message: r.message, usage: r.usage, shown: Boolean(r.entries) }
   },
   jobs: (c) => jobNote(c as unknown as NoteCase),
+  // The instruction chain (filesystem.md): the CLI's own walk, with the case's files and grants as
+  // what it may read.
+  instructions: (c) => {
+    const files = new Set(c.files as string[])
+    return instructionChain(c.boundary as string, c.start as string, (p) => files.has(p) && readableUnder(c.grants as Record<string, string> | undefined, p))
+  },
   library_scope: (c) => resolveBase(c.bases as { id: string; name: string }[], c.base as string | null),
   toolcall_index: (c) => {
     // The deltas as the OpenAI stream carries them: `function.name` and `function.arguments`.