diff --git a/.claude/commands/syncro.md b/.claude/commands/syncro.md
index 73c3b752..52270651 100644
--- a/.claude/commands/syncro.md
+++ b/.claude/commands/syncro.md
@@ -92,6 +92,21 @@ $PYTHON -c "import datetime; d = datetime.date(YYYY, M, D); print(d.strftime('%A
 
 If any check fails, complete the missing step before reporting done. This rule fires on initial estimate creation AND on every subsequent "add X to the estimate" request. Incident: 2026-05-22, UPS added to estimate #7189 without a ticket note — caught by Winter.
 
+**Emailing an invoice/estimate returns 200 "Email sent" even when it reached NOBODY — never
+report delivery from the 200 alone.** `POST /invoices/{id}/email` and `/estimates/{id}/email`
+take no recipient param; Syncro picks it from the record. If `customer.email` is null (and no
+recipient contact is flagged), the send is a silent no-op that still returns HTTP 200. Before
+emailing, confirm the customer has a valid `email`. Note `customer.email` is **UNIQUE
+tenant-wide** — reusing one returns `{"success":false,"message":["Email has already been
+taken"]}`; a `PUT /customers` that fails returns that error shape (not `{"customer":{...}}`),
+so check `.success` on customer writes instead of assuming a silent no-op.
+
+**Living test-findings log:** `.claude/standards/syncro/test-findings.md` records verified
+behaviors/gotchas discovered while exercising the skill on the Howard Test sandbox
+(customer 36118743). Consult + append to it as new API quirks surface — it is how the skill
+avoids re-learning the same trap. Critical entries are folded into these Hard Rules and the
+Verified Response Shapes table.
+
 ## Implementation
 
 When invoked, use the Syncro REST API via `curl`. All requests include `?api_key=<key>` as query parameter (NOT in header — Syncro uses query param auth).
@@ -568,6 +583,13 @@ Every endpoint's response shape, verified against the live API. Parse exactly as
 | Add schedule line | POST `/schedules/{id}/line_items` | `{"schedule_line_item": {...}}` | `.schedule_line_item.id` |
 | Update schedule line | PUT `/schedules/{id}/line_items/{li_id}` | `{"schedule_line_item": {...}}` | `.schedule_line_item.quantity`, `.schedule_line_item.price_retail` |
 | Delete schedule line | DELETE `/schedules/{id}/line_items/{li_id}` | `{"success": true}` | — |
+| Create customer | POST `/customers` | `{"customer": {...}}` | `.customer.id` |
+| Update customer | PUT `/customers/{id}` | **success** `{"customer": {...}}` / **error** `{"success": false, "message": [...]}` | check `.success` — email is unique tenant-wide |
+| Create contact | POST `/contacts` | **FLAT** `{"id": N, "email": ...}` (NOT wrapped) | `.id` — GET-verify; null-parse ≠ failure |
+| Update contact | PUT `/contacts/{id}` | **FLAT** `{"id": N, ...}` | `.id` — `primary`/`receives_invoices` flags are ignored via API |
+| Create contract | POST `/contracts` | write OK but body does NOT echo the object | GET `/contracts` + match; never retry on null |
+| Email invoice | POST `/invoices/{id}/email` | `{"message": "Email sent."}` | **200 even with NO recipient** — verify `customer.email` first |
+| Email estimate | POST `/estimates/{id}/email` | `{"message": "Email sent"}` | **200 even with NO recipient** — verify `customer.email` first |
 
 **Invoice GET line_items field names differ from ticket line_items:** `item` = product name, `name` = description, `price` = unit rate. Do not use `price_retail` when reading invoice line items.
 
diff --git a/.claude/standards/syncro/test-findings.md b/.claude/standards/syncro/test-findings.md
new file mode 100644
index 00000000..2d6d8c30
--- /dev/null
+++ b/.claude/standards/syncro/test-findings.md
@@ -0,0 +1,51 @@
+# Syncro Skill — Live Test Findings (running log)
+
+Verified behaviors/gotchas discovered while testing `/syncro` against the live tenant on the
+**Howard Test** sandbox customer (`customer_id 36118743`) + RMM-TEST-MACHINE. Newest on top.
+Each entry is a rule the skill must not re-learn. Critical ones are also folded into
+`syncro.md` (operating manual) and `api-reference.md` (breadth reference).
+
+## 2026-07-10 — Phase 1 (PSA CRUD)
+
+**Emailing an invoice/estimate returns 200 "Email sent" even when it delivered to NOBODY.**
+`POST /invoices/{id}/email` and `POST /estimates/{id}/email` take **no recipient param** —
+Syncro picks the recipient from the record server-side. If `customer.email` is null (and no
+contact is a flagged recipient), the API still returns `{"message":"Email sent"}` HTTP 200 but
+nothing is sent. **NEVER report an email as delivered based on the 200 alone.** Ensure the
+customer has a valid `email` (or a recipient contact) BEFORE emailing, and confirm real
+delivery out-of-band when it matters.
+
+**`customer.email` is UNIQUE across the tenant.** `PUT /customers/{id}` with an email already
+used elsewhere returns `{"success":false,"message":["Email has already been taken"]}` and does
+NOT set it. For a test customer that must reach a real person whose address is already in
+Syncro, use plus-addressing (`user+tag@domain`) — unique in Syncro, still routes to the inbox
+IF the mail tenant has plus-addressing enabled (M365: off by default in some tenants — verify).
+
+**`PUT /customers/{id}` uses two different response shapes — always check for the error shape.**
+Success → `{"customer":{...}}`. Validation failure → `{"success":false,"message":[...]}` with
+the field unchanged. Parsing only `.customer.email` hides the failure (looks like a silent
+no-op). Read the raw body / check `.success == false` on customer writes.
+
+**Contacts return a FLAT object, not wrapped.** `POST /contacts` and `PUT /contacts/{id}`
+return `{"id":N,"name":...,"email":...}` directly — NOT `{"contact":{...}}`. Parse `.id`, not
+`.contact.id`. (The wrapped-parse returns null and looks like a failure when the write
+succeeded — a blind retry then DUPLICATES the contact. GET-verify, never retry.)
+
+**Contact recipient flags (`primary`, `receives_invoices`, `receives_reports`) are NOT settable
+via the API** — `PUT /contacts/{id}` accepts them in the body but silently ignores them (stay
+null). To designate an invoice-recipient contact, set it in the Syncro GUI.
+
+**`POST /contracts` write succeeds but the response does not echo the created object** (fields
+parse null). GET `/contracts` and match to confirm creation — never retry on the null.
+
+**`GET /contracts?customer_id=N` does NOT filter server-side** — it returns ALL contracts.
+Filter client-side by `.customer_id`.
+
+**Reinforces the standing rule:** null/blank fields in a Syncro write response are NOT proof of
+failure. Syncro has no idempotency, so a blind retry duplicates. Always GET the resource to
+confirm true state before any follow-up action.
+
+### Verified-working this phase (no gotcha, for coverage record)
+POST/GET customer; POST contact; POST ticket (+ number); POST ticket comment (hidden);
+POST add_line_item; POST invoice (from ticket); POST estimate + line_items + PUT recalc;
+POST appointment; POST schedule (paused). All parse under the shapes documented in `syncro.md`.
diff --git a/errorlog.md b/errorlog.md
index 954dab6c..c0cdaa42 100644
--- a/errorlog.md
+++ b/errorlog.md
@@ -19,6 +19,8 @@ Categories (the `[type]` tag): _(none)_ = skill/command execution failure ·
 
 <!-- Append entries below this line -->
 
+2026-07-10 | Howard-Home | syncro/email | [correction] assumed HTTP 200 {message:Email sent} meant the invoice/estimate actually reached the customer; correct is Syncro returns 200 even when customer.email is null (no recipient) - must verify a valid, UNIQUE customer.email before claiming delivery [ctx: customer=36118743 endpoints=POST_/invoices/{id}/email,/estimates/{id}/email]
+
 2026-07-10 | Howard-Home | syncro/assets | [correction] assumed asset writes (POST/PUT create-update), policy_folder_id move, patches, and installed_applications were not doable via the public API; correct is the endpoints exist per the live OpenAPI spec and the prior 'policy_folder_id silently ignored' was a token missing the 'Assets - Policy Change' scope, not an API limitation [ctx: ref=reference-syncro-rmm-api-gui-only endpoint=PUT_/customer_assets/{id}]
 
 2026-07-10 | GURU-BEAST-ROG | guruscan | detached full-chain wrapper died mid-RKill on TPM-PC (marker never written, task->Ready, rkill.log completed fine as orphan) — RKill's process sweep almost certainly killed its own hidden SYSTEM powershell parent; relaunched with -SkipScanners RKill [ctx: host=TPM-PC client=mineralogical-record chain-design-issue]