ver 1.5.1 — duplicate-gate precision (common tokens, cross-kind)

Live 1.5.0 use caught the gate blocking a decision note over the single
vault-common token "echo" (min-normalized overlap gives any one-token
entity a 1.0 score). New echo_index.gate_candidates() + token_df():

- gate blocks same-kind candidates only; cross-kind name collisions
  (a decision titled after its project) warn instead of blocking
- a lone shared token blocks only when unique to that entity (df == 1);
  multi-token overlaps still block

fuzzy_candidates (advisory warnings) and exit-76/--merge-into/--force
semantics unchanged. +3 offline unit tests, gate e2e cases restructured
+2 new; verified live both directions. All suites green.

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

echo-memory.plugin.src/skills/echo-memory/scripts/test_echo_client.py

@@ -148,6 +148,51 @@ def test_fuzzy_candidates_ignores_common_and_short_tokens() -> None:
     assert echo_index.fuzzy_candidates(index, "data pipeline") == []
 
 
+def test_gate_candidates_blocks_same_kind_rare_token() -> None:
+    # The blocking case the gate exists for: same kind, and the shared token is unique
+    # to that one entity — "Robert Smith" vs the person bob-smith must gate.
+    index = {"entities": {"bob-smith": {"path": "resources/people/bob-smith.md",
+                                        "kind": "person", "title": "Bob Smith",
+                                        "aliases": []}}}
+    gated = echo_index.gate_candidates(index, "Robert Smith", kind="person")
+    assert gated and gated[0][0] == "bob-smith"
+
+
+def test_gate_candidates_skips_cross_kind() -> None:
+    # A company/decision named after a person or project is intentional naming, not a
+    # duplicate — cross-kind lookalikes warn but never block.
+    index = {"entities": {"bob-smith": {"path": "resources/people/bob-smith.md",
+                                        "kind": "person", "title": "Bob Smith",
+                                        "aliases": []}}}
+    assert echo_index.gate_candidates(index, "Smith Consulting", kind="company") == []
+    # ...but the advisory candidate list still surfaces it:
+    assert echo_index.fuzzy_candidates(index, "Smith Consulting")
+
+
+def test_gate_candidates_skips_single_vault_common_token() -> None:
+    # The live 1.5.0 false positive: "echo" appears in many entity names, so any title
+    # containing it scored 1.0 against every single-token "echo" entity. A lone shared
+    # token only blocks when it is unique to that entity (df == 1).
+    ents = {
+        "echo": {"path": "projects/active/echo.md", "kind": "project",
+                 "title": "echo", "aliases": []},
+        "echo-v-05": {"path": "projects/archived/echo-v.05.md", "kind": "project",
+                      "title": "echo-v.05", "aliases": []},
+    }
+    assert echo_index.gate_candidates({"entities": ents}, "echo handbook",
+                                      kind="project") == []
+    # multi-token overlap still blocks, even when the individual tokens are common:
+    ents["echo-memory-system"] = {"path": "projects/active/echo-memory-system.md",
+                                  "kind": "project", "title": "echo memory system",
+                                  "aliases": []}
+    ents["echo-memory-notes"] = {"path": "resources/concepts/echo-memory-notes.md",
+                                 "kind": "concept", "title": "echo memory notes",
+                                 "aliases": []}
+    gated = echo_index.gate_candidates({"entities": ents}, "echo memory platform",
+                                       kind="project")
+    assert [s for s, _, _ in gated] == ["echo-memory-system"]
+
+
 def test_aliases_in_frontmatter_flow_and_block() -> None:
     flow = '---\ntype: project\naliases: ["echo memory", "echo plugin"]\n---\n# x\n'
     assert echo_index.aliases_in_frontmatter(flow) == ["echo memory", "echo plugin"]