# Heading resolver broken: `Target-Type: heading` PATCH and `GET /heading/...` both fail on any valid heading (4.1.1)

## Summary

In Obsidian Local REST API **4.1.1**, two endpoints that both rely on heading resolution always fail, even on a freshly written file with trivially-valid markdown headings:

- `PATCH /vault/<path>` with `Target-Type: heading` → HTTP 400 `invalid-target`
- `GET /vault/<path>/heading/<heading-text>` → HTTP 404 `Not Found`

`Target-Type: frontmatter` PATCH on the same file works fine, so the PATCH route itself is healthy. The bug is isolated to the heading-resolution code path shared by these two endpoints.

Also reproduced in **3.6** before upgrading; the 3.6 → 4.1.1 upgrade did not change the behavior.

## Minimal reproducer

The setup writes a clean file with LF-only line endings, then exercises both heading endpoints and one frontmatter endpoint as a control.

```bash
HOST="https://YOUR-HOST:27124"
KEY="YOUR_API_KEY"

# 1. PUT a fresh, simple file (HTTP 204 expected)
cat > /tmp/repro.md <<'EOF'
---
type: scratch
---

# Hello

## Section A

Content under A.

## Section B

Content under B.
EOF

curl -sk -w "PUT: %{http_code}\n" -X PUT \
  -H "Authorization: Bearer $KEY" \
  -H "Content-Type: text/markdown" \
  --data-binary @/tmp/repro.md \
  "$HOST/vault/scratch/repro.md"

# 2. PATCH append under heading "Section A" — expected 200, actual 400 invalid-target
echo "appended" > /tmp/p.md
curl -sk -w "\nPATCH heading: %{http_code}\n" -X PATCH \
  -H "Authorization: Bearer $KEY" \
  -H "Operation: append" \
  -H "Target-Type: heading" \
  -H "Target: Section A" \
  -H "Content-Type: text/markdown" \
  --data-binary @/tmp/p.md \
  "$HOST/vault/scratch/repro.md"

# 3. GET the heading's content via URL path — expected 200, actual 404
curl -sk -w "\nGET heading: %{http_code}\n" \
  -H "Authorization: Bearer $KEY" \
  "$HOST/vault/scratch/repro.md/heading/Section%20A"

# 4. CONTROL: PATCH frontmatter — works (HTTP 200)
curl -sk -w "\nPATCH frontmatter: %{http_code}\n" -X PATCH \
  -H "Authorization: Bearer $KEY" \
  -H "Operation: replace" \
  -H "Target-Type: frontmatter" \
  -H "Target: type" \
  -H "Content-Type: application/json" \
  --data '"updated"' \
  "$HOST/vault/scratch/repro.md"
```

## Actual output

```
PUT: 204

{"message":"The patch you provided could not be applied to the target content.\ninvalid-target","errorCode":40080}
PATCH heading: 400

{"message":"Not Found","errorCode":40400}
GET heading: 404

PATCH frontmatter: 200
```

## Variations tried (all fail identically with `invalid-target` / 404)

- Single-word heading (`Target: Section`) and multi-word (`Target: Section A`)
- URL-encoded header value (`Target: Section%20A`)
- `Operation: append`, `prepend`, and `replace`
- Both freshly-PUT files (LF endings) and files originally written by Obsidian
- `Target-Type: block` also returns `invalid-target` — possibly the same resolver

## What I ruled out

- **CRLF / BOM in source file** — fresh file was written by `curl --data-binary` with LF-only content.
- **Spaces in heading text** — single-word headings fail the same way.
- **URL encoding of `Target:` header value** — raw and percent-encoded both fail.
- **PATCH route generally broken** — `Target-Type: frontmatter` succeeds on the same file.
- **Version regression in 4.1.1** — same behavior in 3.6 before upgrading.

## Environment

- Obsidian Local REST API: **4.1.1** (also reproduced in 3.6)
- Obsidian: <fill in your Obsidian app version>
- OS hosting Obsidian: <fill in>
- Client: `curl` over HTTPS to `:27124` with `-k` (self-signed cert)
- Vault is on local NTFS / ext4 / APFS (fill in)

## Suspected cause

The heading resolver appears to be returning "not found" for every valid heading. Since `GET /vault/<path>/heading/<name>` and the `Target-Type: heading` PATCH variant both fail in lockstep (and frontmatter resolution works fine on the same request path), the most likely location is whichever helper enumerates headings within a parsed file's AST — perhaps it's getting an empty list, or matching on a wrong field.

Happy to bisect or add logging if you can point me at the relevant file.