Add json/csv support to the posting script (issue #012)

TEXT_KINDS and TEXT_SUFFIXES now include json/csv, with matching
sniff_text_kind branches so both explicit --kind and positional auto-mode
work. Added validate_payload's JSON shape check mirroring the server.
Updated SKILL.md/docs/llm_posting_helper.md with real usage examples,
replacing the stale --as-markdown workaround guidance (kept only for
genuinely unstructured code, which still has no dedicated kind). Also
fixed an unrelated stale doc line found in the same table: html_full's
validation was documented as requiring <!doctype AND <html, but only
<html is actually required.

Verified via dry-run (explicit --kind, auto-mode, invalid-JSON rejection)
and one real end-to-end post through the script against the live dev
instance.

Added tests/scripts/test_daybook_post.py - 17 tests, plain unittest, zero
new dependencies, loaded via importlib since the script isn't a package.
Closes the test-coverage question the issue raised.

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

skills/daybook-posting/SKILL.md

@@ -93,7 +93,18 @@ python skills/daybook-posting/scripts/daybook_post.py report.md
 The image is linked to the artifact that references it and is deleted along with it.
 Unreferenced uploads are cleaned up after 24 hours.
 
-For CSV, JSON, or code that should render today, use `--file path --as-markdown` to post it as a Markdown fenced code block. Without `--as-markdown`, these upload as downloadable binary files.
+For CSV and JSON, use `--kind csv`/`--kind json` with `--content-file` — or
+just post the file positionally; auto-mode detects `.csv`/`.json` and picks
+the right kind automatically:
+
+```bash
+python skills/daybook-posting/scripts/daybook_post.py results.csv
+python skills/daybook-posting/scripts/daybook_post.py --kind json --title "Run Summary" --content-file summary.json
+```
+
+For other code that should render today, use `--file path --as-markdown` to
+post it as a Markdown fenced code block. Without `--as-markdown`, it uploads
+as a downloadable binary file.
 
 ## Rules
 

skills/daybook-posting/scripts/daybook_post.py

@@ -18,8 +18,8 @@ from urllib.parse import urljoin
 from urllib.request import Request, urlopen
 
 
-TEXT_KINDS = {"markdown", "html_fragment", "html_full", "deck"}
-TEXT_SUFFIXES = {".md", ".markdown", ".txt", ".html", ".htm"}
+TEXT_KINDS = {"markdown", "html_fragment", "html_full", "deck", "json", "csv"}
+TEXT_SUFFIXES = {".md", ".markdown", ".txt", ".html", ".htm", ".json", ".csv"}
 DEFAULT_URL = "http://127.0.0.1:8001"
 DEFAULT_SOURCE = "agent"
 
@@ -156,6 +156,10 @@ def resolve_auto_path(args):
 def sniff_text_kind(suffix, text):
     if suffix in (".md", ".markdown", ".txt"):
         return "markdown"
+    if suffix == ".json":
+        return "json"
+    if suffix == ".csv":
+        return "csv"
     lower = text.lower()
     if "<!doctype" in lower or "<html" in lower:
         return "html_full"
@@ -301,6 +305,11 @@ def validate_payload(payload, args):
         raise ValueError("html_full must be a complete HTML document with <html> (and ideally <!doctype html>)")
     if kind == "markdown" and not payload["content"].strip():
         raise ValueError("markdown content cannot be blank")
+    if kind == "json":
+        try:
+            json.loads(payload["content"])
+        except json.JSONDecodeError as exc:
+            raise ValueError(f"json content must be valid JSON: {exc}") from exc
 
 
 def print_dry_run(base_url, token, payload, args):