fix(imex): name the physical head in M104/M109 tool indices

M104/M109 address a heater, but every caller of the instance
GCodeWriter::set_temperature overload addresses filaments by logical id, so on a
printer whose physical_extruder_map is not the identity the emitted T named the
wrong head -- or, where the logical id exceeds the head count, no head at all.
With a map of 0,0,0,0,1,2,3 a toolchange to filament 5 emitted "M109 S265 T4"
and "M104 S190 T4 ;cooldown" while the head it meant was T1.

Upstream already treats these commands as physical: the preheat it injects in
GCodeProcessor maps through the same map before emitting, and BBS's own wipe
tower does likewise. Emitting logical is the half that never got the memo.

That mismatch also disabled the cooldown suppression beside the preheat, which
compares the line's T against pem[tool_number] and so never matched a logical
one -- 171 cooldowns survived in a two-head print where none should have. Worse,
it could match the wrong line: a cooldown for filament 1 emitted T1, and a
toolchange to filament 5 gives pem[4] == 1, so a legitimate cooldown for head 0
was deleted because the incoming head happened to be numbered 1.

Translate once, in the instance overload every logical-space caller passes
through. The static overload is already physical-in and is left alone.

Gated on is_imex. physical_extruder_map carries two readings in this tree: the
BBS paths index it by extruder id, the IMEX paths by filament id, and the two
coincide only when the filament and nozzle counts match. Mapping unconditionally
would impose the IMEX reading on profiles that mean the other one --
fdm_bbl_3dp_002_common ships a non-identity [1,0], spared today only because
single_extruder_multi_material suppresses the T qualifier entirely.

The wipe tower's interface-temperature pass has to move with it. It strips the
M109 that post_toolchange emits by searching for that filament's tool index, so
it now searches for the mapped one; left alone it would have stopped matching,
and the surviving blocking M109 would have silently defeated the interface
temperature. Its sibling pass reads WipeTower2 output, which emits no T at all,
and is deliberately unchanged.

The bare T<n> toolchange stays logical -- it selects an AFC lane, not a heater.

Test slices two objects across a head boundary, the only case that reaches this
emission: the same-physical short-circuit in set_extruder suppresses the
cooldown entirely for lane swaps within one head. It scans every M104/M109
rather than matching fixed strings, so it catches any unmapped emission and not
just the two sites changed here. With the mapping neutered it reports 101
offending lines; with it in place, none.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

tests/fff_print/test_multifilament.cpp

@@ -894,6 +894,59 @@ TEST_CASE("IQEX modes emit first- and second-layer temperatures for every active
     CHECK(gcode.find("M104 S240 T3") != std::string::npos);
 }
 
+// M104/M109 name a physical heater, but every caller of the instance set_temperature overload
+// addresses filaments by logical id. pem routes filament 5 (logical 4) to head 1, so a
+// toolchange between filaments 1 and 5 must cool and wait on T1 -- never T4, which on this
+// machine is an AFC lane index and names no heater at all.
+//
+// Regression: the same-physical short-circuit in set_extruder hides this for lane swaps within
+// one head (filaments 1-4 all map to head 0, so no cool-down is emitted), so only a toolchange
+// that CROSSES heads reaches the emission. Ooze prevention must be on for pre/post_toolchange
+// to run at all.
+TEST_CASE("IMEX heater commands name the physical head, not the logical filament",
+          "[MultiFilament][IMEX][Regression]")
+{
+    DynamicPrintConfig config = multifilament_config(7);
+    imex_7x4_printer(config);
+    config.set_deserialize_strict({
+        { "imex_parallel_mode",                "primary" },
+        { "ooze_prevention",                   "1" },
+        { "standby_temperature_delta",         "-50" },
+        { "single_extruder_multi_material",    "0" },
+        { "nozzle_temperature_initial_layer",  "200,200,200,200,200,200,200" },
+        { "nozzle_temperature",                "240,240,240,240,240,240,240" },
+    });
+
+    // Two objects on filaments 1 and 5: logical 0 -> head 0, logical 4 -> head 1.
+    const std::vector<std::vector<ConfigBase::SetDeserializeItem>> overrides{
+        { { "extruder", "1" } },
+        { { "extruder", "5" } },
+    };
+    const std::string gcode = slice_with_object_overrides({ cube(20), cube(20) }, config, overrides);
+
+    // The bare toolchange stays LOGICAL -- it is an AFC lane selector, not a heater.
+    CHECK(gcode.find("\nT4") != std::string::npos);
+
+    // Every heater command carrying a tool must name a configured head (0-3 here), never a
+    // logical slot above the head count. Scanning beats a fixed-string check: it fails on any
+    // stray unmapped emission, not just the two sites this test was written for.
+    std::istringstream ss(gcode);
+    std::string        line;
+    std::vector<std::string> offenders;
+    while (std::getline(ss, line)) {
+        if (line.rfind("M104", 0) != 0 && line.rfind("M109", 0) != 0)
+            continue;
+        const size_t t = line.find(" T");
+        if (t == std::string::npos || t + 2 >= line.size() || !std::isdigit((unsigned char) line[t + 2]))
+            continue;
+        if (std::stoi(line.substr(t + 2)) > 3)
+            offenders.push_back(line);
+    }
+    INFO("heater commands naming a non-existent head: " << offenders.size()
+         << (offenders.empty() ? "" : " e.g. " + offenders.front()));
+    CHECK(offenders.empty());
+}
+
 // The IMEX Primary tool prints the sliced paths directly, so it can only use a filament the
 // printer's physical_extruder_map routes to it. The ghost filament picker enforces that for
 // the secondary tools; the primary's filament comes from the ordinary object selector, which