Phase 1: mechanical echo→chorus rename with back-compat shims

Identity rename, no behavior change (CHORUS-PLAN.md Phase 1):
- Plugin echo-memory → chorus-memory: manifest (v2.0.0-alpha.1), skill dir,
  16 scripts (chorus.py, chorus_config.py, …), EchoError → ChorusError,
  /chorus-* commands, hook paths, docs, scaffold seeds, eval harness,
  build.py. Docs endpoint → chorusapi.mpm.to.
- Env ECHO_* → CHORUS_*; config → ~/.claude/chorus-memory/config.json;
  state dir → ~/.chorus-memory/; marker → _agent/chorus-vault.md.

Back-compat shims (one major version):
- chorus_config aliases legacy ECHO_* env at import; reads a legacy
  echo-memory config.json when no CHORUS config exists (writes never
  land there); doctor/config report the legacy source.
- State dir honors an existing ~/.echo-memory when the new dir is absent
  (offline queue not stranded).
- Marker dual-probe in load/doctor/bootstrap/lint/sweep/migrate: a
  pre-fork _agent/echo-vault.md counts as bootstrapped; bootstrap repair
  won't write a second marker; routing gains agent-marker-legacy (GET).

Verified: 25/25 unit tests, scaffold + routing-sync checks, 4 mock e2e
suites, run_eval metrics unchanged, +6 shim smoke tests green.
Rebuilt chorus-memory.plugin (79 entries).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

eval/test_patch_semantics.py

@@ -3,7 +3,7 @@
 
 These are exactly the behaviors the shipped naive mock cannot reproduce (it appends
 everything at EOF), so without this the section-replace / section-append / missing-
-heading / frontmatter-replace paths are untested. Drives the real echo.py against
+heading / frontmatter-replace paths are untested. Drives the real chorus.py against
 mock_olrapi_hifi.py.
 
 Run:  python test_patch_semantics.py [--port 8820]
@@ -20,7 +20,7 @@ import urllib.request
 from pathlib import Path
 
 HERE = Path(__file__).resolve().parent
-ECHO = HERE.parent / "echo-memory.plugin.src" / "skills" / "echo-memory" / "scripts" / "echo.py"
+CHORUS = HERE.parent / "chorus-memory.plugin.src" / "skills" / "chorus-memory" / "scripts" / "chorus.py"
 KEY = "test-key-not-a-real-secret"
 
 failures = []
@@ -58,9 +58,9 @@ def main():
     srv = subprocess.Popen([sys.executable, str(HERE / "mock_olrapi_hifi.py"), "--port", str(a.port)],
                            stdout=subprocess.PIPE, stderr=subprocess.STDOUT, text=True)
 
-    def echo(*args):
-        env = dict(os.environ, ECHO_BASE=base, ECHO_KEY=KEY, ECHO_VERIFY="0")
-        return subprocess.run([sys.executable, str(ECHO), *args], capture_output=True, text=True, env=env)
+    def chorus(*args):
+        env = dict(os.environ, CHORUS_BASE=base, CHORUS_KEY=KEY, CHORUS_VERIFY="0")
+        return subprocess.run([sys.executable, str(CHORUS), *args], capture_output=True, text=True, env=env)
 
     def ground(path):
         _, body = http("GET", f"{base}/__debug__?path={path}")
@@ -80,30 +80,30 @@ def main():
 
         # replace: Scope body becomes new; Other untouched.
         http("PUT", f"{base}/vault/{doc}", seed)
-        echo("patch", doc, "replace", "heading", "Doc::Scope", tmp("new scope"))
+        chorus("patch", doc, "replace", "heading", "Doc::Scope", tmp("new scope"))
         g = ground(doc) or ""
         check("heading replace swaps section body", "new scope" in g and "old scope" not in g, g)
         check("heading replace leaves sibling section intact", "## Other\nkeep me" in g, g)
 
         # append: lands INSIDE the section (before '## Other'), not at EOF.
-        echo("patch", doc, "append", "heading", "Doc::Scope", tmp("appended line"))
+        chorus("patch", doc, "append", "heading", "Doc::Scope", tmp("appended line"))
         g = ground(doc) or ""
         check("heading append inserts within the section (not EOF)",
               "appended line" in g and g.index("appended line") < g.index("## Other"), g)
 
         # prepend: lands at the TOP of the section body.
-        echo("patch", doc, "prepend", "heading", "Doc::Scope", tmp("first line"))
+        chorus("patch", doc, "prepend", "heading", "Doc::Scope", tmp("first line"))
         g = ground(doc) or ""
         check("heading prepend inserts at section top",
               "first line" in g and g.index("first line") < g.index("new scope"), g)
 
-        # missing heading -> 400 -> echo.py exits non-zero (the silent-loss guard).
-        r = echo("patch", doc, "append", "heading", "Doc::Nope", tmp("lost?"))
+        # missing heading -> 400 -> chorus.py exits non-zero (the silent-loss guard).
+        r = chorus("patch", doc, "append", "heading", "Doc::Nope", tmp("lost?"))
         check("missing heading fails loud (non-zero exit)", r.returncode != 0, r.stderr)
         check("missing heading does not write", "lost?" not in (ground(doc) or ""))
 
         # frontmatter replace on an existing field updates it.
-        echo("fm", doc, "updated", "2026-06-22")
+        chorus("fm", doc, "updated", "2026-06-22")
         g = ground(doc) or ""
         check("frontmatter replace updates existing field", "updated: 2026-06-22" in g, g)
 
@@ -112,7 +112,7 @@ def main():
         # every other line is preserved. (The old contract failed loud on exactly the
         # notes that needed repair.)
         before = ground(doc) or ""
-        r = echo("fm", doc, "nonexistent_field", "x")
+        r = chorus("fm", doc, "nonexistent_field", "x")
         check("fm creates a missing field (create-or-replace)", r.returncode == 0,
               r.stderr or r.stdout)
         g = ground(doc) or ""
@@ -121,7 +121,7 @@ def main():
               all(line in g for line in before.splitlines() if line.strip()), g)
 
         # raw `patch replace frontmatter` (no fallback) still fails loud on a missing key.
-        r = echo("patch", doc, "replace", "frontmatter", "still_missing", tmp('"x"'))
+        r = chorus("patch", doc, "replace", "frontmatter", "still_missing", tmp('"x"'))
         check("raw frontmatter PATCH of a missing field fails loud", r.returncode != 0, r.stderr)
 
         print(f"\n{len(failures)} failure(s)" if failures else "\nall PATCH-semantics tests passed")