diff --git a/R/loadfast.R b/R/loadfast.R
index 5f9255f..6c54503 100644
--- a/R/loadfast.R
+++ b/R/loadfast.R
@@ -227,6 +227,9 @@ load_fast <- function(path = ".", helpers = TRUE, attach_testthat = NULL, full =
       "]"
     )
 
+    .loadfast.run_onload(ns_env, abs_path, pkg_name)
+    .timer("incr .onLoad")
+
     .loadfast.source_helpers(abs_path, pkg_env, helpers, attach_testthat, pkg_name)
     .timer("TOTAL (incremental)")
     return(invisible(ns_env))
@@ -398,6 +401,9 @@ load_fast <- function(path = ".", helpers = TRUE, attach_testthat = NULL, full =
   }
   .timer("attach testthat")
 
+  .loadfast.run_onload(ns_env, abs_path, pkg_name)
+  .timer(".onLoad")
+
   pkg_env <- attach(NULL, name = pkg_env_name)
   list2env(as.list(ns_env, all.names = FALSE), envir = pkg_env)
   list2env(as.list(impenv, all.names = TRUE), envir = pkg_env)
@@ -496,6 +502,17 @@ load_fast_register_reload <- function(path = ".", files, reason = NULL) {
   invisible(TRUE)
 }
 
+.loadfast.run_onload <- function(ns_env, abs_path, pkg_name) {
+  if (!exists(".onLoad", envir = ns_env, inherits = FALSE)) return(invisible(NULL))
+  tryCatch(
+    get(".onLoad", envir = ns_env, inherits = FALSE)(dirname(abs_path), pkg_name),
+    error = function(e) {
+      warning("Error in .onLoad() for '", pkg_name, "': ", conditionMessage(e), call. = FALSE)
+    }
+  )
+  invisible(NULL)
+}
+
 .loadfast.source_one <- function(f, ns_env) {
   s4_pattern <- "no definition for class"
   tryCatch(
diff --git a/TECHNICAL_DEBT.md b/TECHNICAL_DEBT.md
index 640c26d..92a44c8 100644
--- a/TECHNICAL_DEBT.md
+++ b/TECHNICAL_DEBT.md
@@ -48,24 +48,6 @@ If the `Package:` field in `DESCRIPTION` changes in place for the same directory
 
 ## Low-priority debt
 
-### 5. Load hook behavior is not explicitly tested
-**Why this matters**
-
-The loader aims to behave like a practical development-time package loader, but the test suite does not currently pin down the behavior of `.onLoad()` and `.onAttach()` hooks.
-
-**Risk**
-- Hook execution semantics may drift unnoticed during refactors
-- Full and incremental loads may behave inconsistently
-- Package state initialized by hooks may be wrong in edge cases
-
-**Preferred fix**
-- Add focused tests that define and exercise `.onLoad()` / `.onAttach()` in a temp package
-- Verify behavior on first load, incremental reload, and `full = TRUE`
-- Document any intentional differences from `devtools::load_all()`
-
-**Priority**
-- Low
-
 ## Low-priority debt
 
 ### 3. Testthat detection logic is duplicated
diff --git a/test_loadfast.R b/test_loadfast.R
index 1b02b21..f93ec7f 100644
--- a/test_loadfast.R
+++ b/test_loadfast.R
@@ -1931,6 +1931,62 @@ check("lockfile: full reload resets warning baseline", quote(
   !any(grepl("renv.lock changed", lock_reload_full$warnings))
 ))
 
+# --- 4l: .onLoad hook is called during full and incremental loads ---
+cat("\n--- 4l: .onLoad hook execution ---\n\n")
+
+tmp_onload <- tempfile("loadfast_onload_")
+copy_baseline(tmp_onload)
+remove_renv_lock(tmp_onload)
+
+writeLines(c(
+  ".onLoad_call_count <- 0L",
+  ".onLoad <- function(libname, pkgname) {",
+  "  .onLoad_call_count <<- .onLoad_call_count + 1L",
+  "  .onLoad_libname <<- libname",
+  "  .onLoad_pkgname <<- pkgname",
+  "}"
+), file.path(tmp_onload, "R", "zzz.R"))
+
+ns_onload <- load_fast(tmp_onload, helpers = FALSE, attach_testthat = FALSE)
+
+check(".onLoad: is called on full load", quote(
+  exists(".onLoad_call_count", envir = ns_onload, inherits = FALSE) &&
+    get(".onLoad_call_count", envir = ns_onload) == 1L
+))
+
+check(".onLoad: receives correct pkgname", quote(
+  get(".onLoad_pkgname", envir = ns_onload) == "devpackage"
+))
+
+check(".onLoad: receives dirname(abs_path) as libname", quote(
+  identical(
+    normalizePath(get(".onLoad_libname", envir = ns_onload), mustWork = FALSE),
+    normalizePath(dirname(tmp_onload), mustWork = FALSE)
+  )
+))
+
+# Incremental reload — nothing changed => short-circuit, .onLoad not re-called
+ns_onload_nochg <- load_fast(tmp_onload, helpers = FALSE, attach_testthat = FALSE)
+
+check(".onLoad: not called again on no-change reload", quote(
+  get(".onLoad_call_count", envir = ns_onload_nochg) == 1L
+))
+
+# Trigger an incremental reload by modifying base.R
+writeLines(c(
+  "add <- function(a, b) a + b + 9999"
+), file.path(tmp_onload, "R", "base.R"))
+
+ns_onload_incr <- load_fast(tmp_onload, helpers = FALSE, attach_testthat = FALSE)
+
+check(".onLoad: called again on incremental reload (files changed)", quote(
+  get(".onLoad_call_count", envir = ns_onload_incr) == 2L
+))
+
+check(".onLoad: add() reflects incremental change", quote(
+  get("add", envir = ns_onload_incr)(1, 2) == 10002
+))
+
 # ============================================================================
 # Summary
 # ============================================================================