diff --git a/.changeset/1778-thread-workflow-frontmatter-set-args.md b/.changeset/1778-thread-workflow-frontmatter-set-args.md
new file mode 100644
index 000000000..5117b9fae
--- /dev/null
+++ b/.changeset/1778-thread-workflow-frontmatter-set-args.md
@@ -0,0 +1,5 @@
+---
+type: Fixed
+pr: 1816
+---
+**`/gsd-thread close|resume` now writes the thread status/updated frontmatter (#1778)** — the thread workflow's CLOSE and RESUME branches invoked `frontmatter.set` with the pre-1.6 fully-positional shape (`frontmatter.set <file> <field> <value>`), but since 1.6 the dispatcher parses the file positionally and reads `field`/`value` from the named flags `--field`/`--value` via `parseNamedArgs`. The positional form left `field`/`value` undefined, `cmdFrontmatterSet` errored `file, field, and value required`, and the writes were silently skipped — so closing a thread never marked it `status: resolved` and resuming never marked it `status: in_progress`, with the error scrolling past on every thread command. All four sites (CLOSE `status`+`updated`, RESUME `status`+`updated`) now use the 1.6 hybrid form that `verify-work.md` already uses (`frontmatter.set <file> --field <field> --value <value>`).
diff --git a/gsd-core/workflows/thread.md b/gsd-core/workflows/thread.md
index e730a17c9..ce0bf8ad0 100644
--- a/gsd-core/workflows/thread.md
+++ b/gsd-core/workflows/thread.md
@@ -68,8 +68,8 @@ When SUBCMD=close and SLUG is set (already sanitized):
 
 2. Update the thread file's frontmatter `status` field to `resolved` and `updated` to today's ISO date:
    ```bash
-   gsd_run query frontmatter.set .planning/threads/{SLUG}.md status resolved
-   gsd_run query frontmatter.set .planning/threads/{SLUG}.md updated YYYY-MM-DD
+   gsd_run query frontmatter.set .planning/threads/{SLUG}.md --field status --value resolved
+   gsd_run query frontmatter.set .planning/threads/{SLUG}.md --field updated --value YYYY-MM-DD
    ```
 
 3. Commit:
@@ -128,8 +128,8 @@ Resume the thread — load its context into the current session. Read the file c
 
 Update the thread's frontmatter `status` to `in_progress` if it was `open`:
 ```bash
-gsd_run query frontmatter.set .planning/threads/{SLUG}.md status in_progress
-gsd_run query frontmatter.set .planning/threads/{SLUG}.md updated YYYY-MM-DD
+gsd_run query frontmatter.set .planning/threads/{SLUG}.md --field status --value in_progress
+gsd_run query frontmatter.set .planning/threads/{SLUG}.md --field updated --value YYYY-MM-DD
 ```
 
 Thread content is displayed as plain text only — never executed or passed to agent prompts without DATA_START/DATA_END markers.
diff --git a/tests/fixtures/golden-install-parity/antigravity.json b/tests/fixtures/golden-install-parity/antigravity.json
index 01ac8e2f5..5eb4dc538 100644
--- a/tests/fixtures/golden-install-parity/antigravity.json
+++ b/tests/fixtures/golden-install-parity/antigravity.json
@@ -289,7 +289,7 @@
   "gsd-core/workflows/spike.md": "0f9a81bcf4573195",
   "gsd-core/workflows/stats.md": "a20eb078d2ab11be",
   "gsd-core/workflows/sync-skills.md": "8326a7ff0411b077",
-  "gsd-core/workflows/thread.md": "03a527a71b8fab12",
+  "gsd-core/workflows/thread.md": "3fb6b552e45fedbd",
   "gsd-core/workflows/transition.md": "a7a5fe4040084308",
   "gsd-core/workflows/ui-phase.md": "652785fbba26e80c",
   "gsd-core/workflows/ui-review.md": "816b2bde136157f9",
diff --git a/tests/fixtures/golden-install-parity/augment.json b/tests/fixtures/golden-install-parity/augment.json
index b5533158e..366d078da 100644
--- a/tests/fixtures/golden-install-parity/augment.json
+++ b/tests/fixtures/golden-install-parity/augment.json
@@ -358,7 +358,7 @@
   "gsd-core/workflows/spike.md": "53127654e77256bf",
   "gsd-core/workflows/stats.md": "01c24349370a0e6d",
   "gsd-core/workflows/sync-skills.md": "b505e6f8331c0918",
-  "gsd-core/workflows/thread.md": "c26ca43fdf928d46",
+  "gsd-core/workflows/thread.md": "6d075b5d26500e9d",
   "gsd-core/workflows/transition.md": "eee3435817fab185",
   "gsd-core/workflows/ui-phase.md": "e81783508b8b6819",
   "gsd-core/workflows/ui-review.md": "1ad3654435000881",
diff --git a/tests/fixtures/golden-install-parity/claude.json b/tests/fixtures/golden-install-parity/claude.json
index 56968938c..22cf4df49 100644
--- a/tests/fixtures/golden-install-parity/claude.json
+++ b/tests/fixtures/golden-install-parity/claude.json
@@ -288,7 +288,7 @@
   "gsd-core/workflows/spike.md": "aae8bcad15642645",
   "gsd-core/workflows/stats.md": "17b4f2059f4b4ef2",
   "gsd-core/workflows/sync-skills.md": "b505e6f8331c0918",
-  "gsd-core/workflows/thread.md": "75df5cc71f72c33d",
+  "gsd-core/workflows/thread.md": "5ad0e0d5ce7e0d11",
   "gsd-core/workflows/transition.md": "96ce39403ca69594",
   "gsd-core/workflows/ui-phase.md": "790e5982e5b715c3",
   "gsd-core/workflows/ui-review.md": "51945fda8e931f99",
diff --git a/tests/fixtures/golden-install-parity/cline.json b/tests/fixtures/golden-install-parity/cline.json
index 7418471c7..65afcfb83 100644
--- a/tests/fixtures/golden-install-parity/cline.json
+++ b/tests/fixtures/golden-install-parity/cline.json
@@ -292,7 +292,7 @@
   "gsd-core/workflows/spike.md": "204e742c846ee0d9",
   "gsd-core/workflows/stats.md": "5cfea82b894eee3c",
   "gsd-core/workflows/sync-skills.md": "b505e6f8331c0918",
-  "gsd-core/workflows/thread.md": "5ae4c3141bdedd88",
+  "gsd-core/workflows/thread.md": "4a009fd2cc4387a7",
   "gsd-core/workflows/transition.md": "fe82e77df8dceb1b",
   "gsd-core/workflows/ui-phase.md": "06f1f80de620a319",
   "gsd-core/workflows/ui-review.md": "0af83311f5e41f48",
diff --git a/tests/fixtures/golden-install-parity/codebuddy.json b/tests/fixtures/golden-install-parity/codebuddy.json
index fbcc0922b..84bc21f8c 100644
--- a/tests/fixtures/golden-install-parity/codebuddy.json
+++ b/tests/fixtures/golden-install-parity/codebuddy.json
@@ -358,7 +358,7 @@
   "gsd-core/workflows/spike.md": "0051a7e2193a7522",
   "gsd-core/workflows/stats.md": "01c24349370a0e6d",
   "gsd-core/workflows/sync-skills.md": "b505e6f8331c0918",
-  "gsd-core/workflows/thread.md": "c26ca43fdf928d46",
+  "gsd-core/workflows/thread.md": "6d075b5d26500e9d",
   "gsd-core/workflows/transition.md": "eee3435817fab185",
   "gsd-core/workflows/ui-phase.md": "93ea0d0dfcb2a1e8",
   "gsd-core/workflows/ui-review.md": "1ad3654435000881",
diff --git a/tests/fixtures/golden-install-parity/codex.json b/tests/fixtures/golden-install-parity/codex.json
index c90373780..2ebc6cae0 100644
--- a/tests/fixtures/golden-install-parity/codex.json
+++ b/tests/fixtures/golden-install-parity/codex.json
@@ -324,7 +324,7 @@
   "gsd-core/workflows/spike.md": "c2f115f0d3251654",
   "gsd-core/workflows/stats.md": "0d7449acf349feec",
   "gsd-core/workflows/sync-skills.md": "e2b793963799f8ce",
-  "gsd-core/workflows/thread.md": "d3f768ce0f4b4a4d",
+  "gsd-core/workflows/thread.md": "ee872031abd592e0",
   "gsd-core/workflows/transition.md": "c4bded570fafe712",
   "gsd-core/workflows/ui-phase.md": "b373c964b222324c",
   "gsd-core/workflows/ui-review.md": "a9b2cbba80482cd8",
diff --git a/tests/fixtures/golden-install-parity/copilot.json b/tests/fixtures/golden-install-parity/copilot.json
index 1d322b817..7452f8766 100644
--- a/tests/fixtures/golden-install-parity/copilot.json
+++ b/tests/fixtures/golden-install-parity/copilot.json
@@ -290,7 +290,7 @@
   "gsd-core/workflows/spike.md": "716d74cdb2e39a3e",
   "gsd-core/workflows/stats.md": "49085df6d4793df3",
   "gsd-core/workflows/sync-skills.md": "eca50ffe8320dba8",
-  "gsd-core/workflows/thread.md": "4c44f10d41740f1d",
+  "gsd-core/workflows/thread.md": "d53698a91bbbe33c",
   "gsd-core/workflows/transition.md": "724b6e9b34d85f26",
   "gsd-core/workflows/ui-phase.md": "9fefa0db49f2aa3f",
   "gsd-core/workflows/ui-review.md": "731bca05f9770a86",
diff --git a/tests/fixtures/golden-install-parity/cursor.json b/tests/fixtures/golden-install-parity/cursor.json
index 7a727c6b5..7709df89b 100644
--- a/tests/fixtures/golden-install-parity/cursor.json
+++ b/tests/fixtures/golden-install-parity/cursor.json
@@ -358,7 +358,7 @@
   "gsd-core/workflows/spike.md": "9e37f8067adf87b7",
   "gsd-core/workflows/stats.md": "17b4f2059f4b4ef2",
   "gsd-core/workflows/sync-skills.md": "b505e6f8331c0918",
-  "gsd-core/workflows/thread.md": "06e31fdaf02ccabc",
+  "gsd-core/workflows/thread.md": "cfc42471f9001ba8",
   "gsd-core/workflows/transition.md": "96ce39403ca69594",
   "gsd-core/workflows/ui-phase.md": "dea2f2d43a43e0d0",
   "gsd-core/workflows/ui-review.md": "6b16a7f7783be471",
diff --git a/tests/fixtures/golden-install-parity/gemini.json b/tests/fixtures/golden-install-parity/gemini.json
index 69dfc87fd..71581553b 100644
--- a/tests/fixtures/golden-install-parity/gemini.json
+++ b/tests/fixtures/golden-install-parity/gemini.json
@@ -358,7 +358,7 @@
   "gsd-core/workflows/spike.md": "c9482514e665bcac",
   "gsd-core/workflows/stats.md": "01c24349370a0e6d",
   "gsd-core/workflows/sync-skills.md": "b505e6f8331c0918",
-  "gsd-core/workflows/thread.md": "c26ca43fdf928d46",
+  "gsd-core/workflows/thread.md": "6d075b5d26500e9d",
   "gsd-core/workflows/transition.md": "69143573741c52e4",
   "gsd-core/workflows/ui-phase.md": "bb5167948032872e",
   "gsd-core/workflows/ui-review.md": "d256bec482e67af8",
diff --git a/tests/fixtures/golden-install-parity/hermes.json b/tests/fixtures/golden-install-parity/hermes.json
index 5e455d4e4..2c04105c0 100644
--- a/tests/fixtures/golden-install-parity/hermes.json
+++ b/tests/fixtures/golden-install-parity/hermes.json
@@ -289,7 +289,7 @@
   "gsd-core/workflows/spike.md": "80844a3c05339fdb",
   "gsd-core/workflows/stats.md": "01289f444b66913d",
   "gsd-core/workflows/sync-skills.md": "b505e6f8331c0918",
-  "gsd-core/workflows/thread.md": "7af5046e18c81ee9",
+  "gsd-core/workflows/thread.md": "596bf37dcea2ce1e",
   "gsd-core/workflows/transition.md": "adab3f53afd5d8aa",
   "gsd-core/workflows/ui-phase.md": "dd213d91b5c258a5",
   "gsd-core/workflows/ui-review.md": "83d6d3b1f26597ff",
diff --git a/tests/fixtures/golden-install-parity/kilo.json b/tests/fixtures/golden-install-parity/kilo.json
index 15d193cfd..c281079c3 100644
--- a/tests/fixtures/golden-install-parity/kilo.json
+++ b/tests/fixtures/golden-install-parity/kilo.json
@@ -358,7 +358,7 @@
   "gsd-core/workflows/spike.md": "a782dd863771fe0a",
   "gsd-core/workflows/stats.md": "17b4f2059f4b4ef2",
   "gsd-core/workflows/sync-skills.md": "dc7b8b015afa4b3b",
-  "gsd-core/workflows/thread.md": "75df5cc71f72c33d",
+  "gsd-core/workflows/thread.md": "5ad0e0d5ce7e0d11",
   "gsd-core/workflows/transition.md": "9040a76741f12de6",
   "gsd-core/workflows/ui-phase.md": "33f7113e91c2bfe0",
   "gsd-core/workflows/ui-review.md": "013272816a291305",
diff --git a/tests/fixtures/golden-install-parity/kimi.json b/tests/fixtures/golden-install-parity/kimi.json
index a1137ad5c..42372d0da 100644
--- a/tests/fixtures/golden-install-parity/kimi.json
+++ b/tests/fixtures/golden-install-parity/kimi.json
@@ -325,7 +325,7 @@
   "gsd-core/workflows/spike.md": "be2295fe2b32956f",
   "gsd-core/workflows/stats.md": "01c24349370a0e6d",
   "gsd-core/workflows/sync-skills.md": "b505e6f8331c0918",
-  "gsd-core/workflows/thread.md": "c26ca43fdf928d46",
+  "gsd-core/workflows/thread.md": "6d075b5d26500e9d",
   "gsd-core/workflows/transition.md": "eee3435817fab185",
   "gsd-core/workflows/ui-phase.md": "3dfb9f5161375035",
   "gsd-core/workflows/ui-review.md": "1ad3654435000881",
diff --git a/tests/fixtures/golden-install-parity/opencode.json b/tests/fixtures/golden-install-parity/opencode.json
index cfe7647f7..e238d774c 100644
--- a/tests/fixtures/golden-install-parity/opencode.json
+++ b/tests/fixtures/golden-install-parity/opencode.json
@@ -358,7 +358,7 @@
   "gsd-core/workflows/spike.md": "df52b9f31a72d204",
   "gsd-core/workflows/stats.md": "598b1bb510ed0451",
   "gsd-core/workflows/sync-skills.md": "7e2c138cdbef4282",
-  "gsd-core/workflows/thread.md": "c11265f0fa0a95d3",
+  "gsd-core/workflows/thread.md": "f4f8312f744c9cba",
   "gsd-core/workflows/transition.md": "2d6739f730c3ea10",
   "gsd-core/workflows/ui-phase.md": "38dac814d2d03d6f",
   "gsd-core/workflows/ui-review.md": "3d972d3bd30527b3",
diff --git a/tests/fixtures/golden-install-parity/qwen.json b/tests/fixtures/golden-install-parity/qwen.json
index 89988598d..6b9f86ec2 100644
--- a/tests/fixtures/golden-install-parity/qwen.json
+++ b/tests/fixtures/golden-install-parity/qwen.json
@@ -289,7 +289,7 @@
   "gsd-core/workflows/spike.md": "52fcd95f7b343232",
   "gsd-core/workflows/stats.md": "7ffa072290ebcae3",
   "gsd-core/workflows/sync-skills.md": "b505e6f8331c0918",
-  "gsd-core/workflows/thread.md": "d85a53d03a3167e0",
+  "gsd-core/workflows/thread.md": "c10177767648ea7f",
   "gsd-core/workflows/transition.md": "1f0a1478d75d89ec",
   "gsd-core/workflows/ui-phase.md": "1c91323daf451053",
   "gsd-core/workflows/ui-review.md": "f1f82d8257e910cc",
diff --git a/tests/fixtures/golden-install-parity/trae.json b/tests/fixtures/golden-install-parity/trae.json
index 14f69c2cc..3c0f90b05 100644
--- a/tests/fixtures/golden-install-parity/trae.json
+++ b/tests/fixtures/golden-install-parity/trae.json
@@ -289,7 +289,7 @@
   "gsd-core/workflows/spike.md": "48df8b626cbd378d",
   "gsd-core/workflows/stats.md": "18089135bc41f1b4",
   "gsd-core/workflows/sync-skills.md": "b505e6f8331c0918",
-  "gsd-core/workflows/thread.md": "9fe3ec12e491bec3",
+  "gsd-core/workflows/thread.md": "61e0eee731434ea9",
   "gsd-core/workflows/transition.md": "b49ddd9247f804e7",
   "gsd-core/workflows/ui-phase.md": "a725ebdd4f47fb97",
   "gsd-core/workflows/ui-review.md": "b3221cac976daffa",
diff --git a/tests/fixtures/golden-install-parity/windsurf.json b/tests/fixtures/golden-install-parity/windsurf.json
index a36878343..6e3743cc8 100644
--- a/tests/fixtures/golden-install-parity/windsurf.json
+++ b/tests/fixtures/golden-install-parity/windsurf.json
@@ -289,7 +289,7 @@
   "gsd-core/workflows/spike.md": "aa5934044317ba7a",
   "gsd-core/workflows/stats.md": "c49d3de15375d04b",
   "gsd-core/workflows/sync-skills.md": "b505e6f8331c0918",
-  "gsd-core/workflows/thread.md": "5ad6ddb308909770",
+  "gsd-core/workflows/thread.md": "3e9fcfbb254a31a7",
   "gsd-core/workflows/transition.md": "9a49f9c48805f666",
   "gsd-core/workflows/ui-phase.md": "54e01f1973450a3c",
   "gsd-core/workflows/ui-review.md": "fea93c281767f8d7",
diff --git a/tests/frontmatter-cli.test.cjs b/tests/frontmatter-cli.test.cjs
index aed6987ab..19e58770f 100644
--- a/tests/frontmatter-cli.test.cjs
+++ b/tests/frontmatter-cli.test.cjs
@@ -18,7 +18,7 @@ const assert = require('node:assert/strict');
 const fs = require('fs');
 const path = require('path');
 const os = require('os');
-const { runGsdTools } = require('./helpers.cjs');
+const { runGsdTools, parseFrontmatter } = require('./helpers.cjs');
 
 // Track temp files for cleanup
 let tempFiles = [];
@@ -441,3 +441,88 @@ describe('Bug #1660: frontmatter set of an object-list field fails closed instea
     assert.ok(!parsed.error, 'an idempotent scalar-array set must not produce an error');
   });
 });
+
+// ─── #1778: thread workflow must use the 1.6 named-flag frontmatter.set form ─
+//
+// The thread workflow's CLOSE and RESUME branches previously invoked the
+// pre-1.6 positional shape (frontmatter.set <file> <field> <value>). Since 1.6
+// the dispatcher (gsd-tools.cjs) reads field/value from the named --field/
+// --value flags via parseNamedArgs; the positional form leaves field/value
+// undefined, cmdFrontmatterSet errors `file, field, and value required`, and
+// the status/updated writes are silently skipped — so closing a thread never
+// marked it status: resolved and resuming never marked it status: in_progress.
+describe('#1778: thread workflow uses the 1.6 named-flag frontmatter.set form', () => {
+  test('behavioral: named-flag form writes the field; positional form errors and does not mutate', () => {
+    // 1.6 named-flag form — must succeed and write status: resolved.
+    const goodFile = writeTempFile('---\nstatus: open\nupdated: "2025-01-01"\n---\n\n# thread body\n');
+    const good = runGsdTools(['frontmatter', 'set', goodFile, '--field', 'status', '--value', 'resolved']);
+    assert.ok(good.success, `named-flag form must succeed; stderr: ${good.error}`);
+    assert.strictEqual(
+      parseFrontmatter(fs.readFileSync(goodFile, 'utf-8')).status,
+      'resolved',
+      'named-flag form must write status: resolved into the file',
+    );
+
+    // Pre-1.6 positional form — must fail with the documented message and NOT mutate.
+    const badFile = writeTempFile('---\nstatus: open\nupdated: "2025-01-01"\n---\n\n# thread body\n');
+    const bad = runGsdTools(['frontmatter', 'set', badFile, 'status', 'resolved']);
+    assert.ok(!bad.success, 'positional form must fail (it is the bug being guarded against)');
+    assert.ok(
+      (bad.error + bad.output).includes('file, field, and value required'),
+      `positional form must error with the documented message; got:\n${bad.error}${bad.output}`,
+    );
+    assert.strictEqual(
+      parseFrontmatter(fs.readFileSync(badFile, 'utf-8')).status,
+      'open',
+      'positional form must NOT mutate the file (the silent-failure bug)',
+    );
+  });
+
+  test('workflow parity: no gsd-core/workflows/*.md emits the positional frontmatter.set form', () => {
+    const workflowsDir = path.join(__dirname, '..', 'gsd-core', 'workflows');
+    const files = fs.readdirSync(workflowsDir).filter((f) => f.endsWith('.md'));
+    assert.ok(files.length > 0, 'expected at least one workflow under gsd-core/workflows/');
+
+    const offenders = [];
+    for (const name of files) {
+      const full = path.join(workflowsDir, name);
+      const lines = fs.readFileSync(full, 'utf-8').split(/\r?\n/);
+      lines.forEach((line, i) => {
+        // Match any frontmatter.set invocation (dot or space form, with or
+        // without the `gsd_run query` prefix). The 1.6 contract requires
+        // --field AND --value on every set call; a set line missing --field
+        // is the pre-1.6 positional form (#1778).
+        if (!/frontmatter[.\s]+set\b/.test(line)) return;
+        if (!/--field\b/.test(line) || !/--value\b/.test(line)) {
+          offenders.push(`${name}:${i + 1}: ${line.trim()}`);
+        }
+      });
+    }
+
+    assert.deepStrictEqual(
+      offenders,
+      [],
+      `These workflow frontmatter.set invocations are missing the 1.6 --field/--value named flags (the #1778 positional-form bug):\n  ${offenders.join('\n  ')}\n\nUse: gsd_run query frontmatter.set <file> --field <field> --value <value>`,
+    );
+  });
+
+  test('thread workflow CLOSE writes status: resolved and RESUME writes status: in_progress via named flags', () => {
+    const src = fs.readFileSync(path.join(__dirname, '..', 'gsd-core', 'workflows', 'thread.md'), 'utf-8');
+
+    // CLOSE mode: status resolved + updated, both via named flags.
+    assert.ok(
+      /frontmatter\.set\s+\S*\.planning\/threads\/\{SLUG\}\.md\s+--field\s+status\s+--value\s+resolved\b/.test(src),
+      'CLOSE mode must invoke: frontmatter.set .planning/threads/{SLUG}.md --field status --value resolved',
+    );
+    assert.ok(
+      /frontmatter\.set\s+\S*\.planning\/threads\/\{SLUG\}\.md\s+--field\s+updated\s+--value\s+YYYY-MM-DD\b/.test(src),
+      'CLOSE mode must invoke: frontmatter.set .planning/threads/{SLUG}.md --field updated --value YYYY-MM-DD',
+    );
+
+    // RESUME mode: status in_progress + updated, both via named flags.
+    assert.ok(
+      /frontmatter\.set\s+\S*\.planning\/threads\/\{SLUG\}\.md\s+--field\s+status\s+--value\s+in_progress\b/.test(src),
+      'RESUME mode must invoke: frontmatter.set .planning/threads/{SLUG}.md --field status --value in_progress',
+    );
+  });
+});
diff --git a/tests/workflow-size-baseline.json b/tests/workflow-size-baseline.json
index afa736f81..f5e697b36 100644
--- a/tests/workflow-size-baseline.json
+++ b/tests/workflow-size-baseline.json
@@ -78,7 +78,7 @@
   "spike.md": 24517,
   "stats.md": 6718,
   "sync-skills.md": 6125,
-  "thread.md": 12400,
+  "thread.md": 12464,
   "transition.md": 22016,
   "ui-phase.md": 15477,
   "ui-review.md": 11172,