Bakari set his phone on the security desk, started the stopwatch, and kept Musa’s coded sequence facedown whenever anyone entered the room. The point was simple: nobody in either apartment would know which source had been changed at which moment.
“Phase A starts now,” he announced in the small group chat.
Halima sat at her studio desk with the new curtain closed and the lamp shield in place. Her laptop was open but untouched. For ten minutes, her job was not to work or defend herself. It was to follow the protocol.
Across the courtyard, Asha had a sheet with three choices: no light, low light, strong light. Musa had told her not to guess the cause. She was to write what she saw, nothing more.
Two minutes later Bakari received her message: **Low light, upper right. Tolerable.**
Halima wanted to identify the source by the shadows in her own room. She stopped herself. If she knew the answer before the observation, the test would become another argument wearing technical clothes.
Musa changed the sequence.
“Phase B.”
Asha answered faster this time: **Broad light. Enters above the curtain. Reaches the bedroom wall.**
No one wrote *your light* or *their light*. The neutral language cooled the room better than any apology could have.
For the third phase Musa combined both sources. Asha sent a photograph of the curtain edge only, preserving the privacy of the room. The image showed a bright narrow line on one side and a softer wash above it. The combination was visibly worse than either source alone.
They repeated the sequence later with a different order. Musa even refused to tell Halima when her own lamp was the active source.
“You too have expectations,” he said. “If you know your lamp is on, you will read her report differently.”
Halima disliked giving up that control, which was exactly why she agreed.
One observation arrived a minute late because Asha had stepped away to get water. Instead of hiding the deviation, they marked it. Musa gave the round less weight but did not discard it. Uncertainty was no longer a weakness someone had to conceal; it was simply part of the record.
Near midnight, Musa moved into the courtyard and photographed the exterior geometry from tape marks on the ground. When the common corridor lamp operated alone, Halima could finally see the reflection with her own eyes. Its beam struck the side wall and returned as a broad wash. From inside her apartment, she had underestimated it because it did not look like a direct beam.
Asha reported her highest broad-light level during that phase.
Then Musa switched off the common light and left Halima’s studio lamp on. With the curtain and shield now installed, Asha reported only a narrow line at one angle.
The results did not give Halima a clean victory. Her adjustments had worked, but her studio still contributed a smaller amount. The common fixture had become the larger source of current disturbance.
After the test, they met downstairs without David. Musa drew three columns and showed them the repeated pattern. Common light: major contributor after Halima’s changes. Studio light: minor contributor at a specific angle. Both together: worst condition.
Asha exhaled. “So I wasn’t imagining it.”
“No,” Halima said. “And I still have a smaller part to fix.”
Musa nodded. “That is the useful answer. Not who won.”
Halima could have photographed the chart and sent Salma a triumphant message: *We proved the building light was the main problem.* She did not. Instead she proposed correcting both sources and testing again after the building repair.
Asha agreed.
That choice cost Halima the simplest version of the story, the one in which later evidence erased her earlier contribution. But it replaced the argument about blame with a two-source problem that could actually be managed.
As Musa packed his papers, he pulled out the old maintenance plan and compared it with the fixture photograph from that night.
One line made the deviation unmistakable: the corridor light had been installed at a different angle from the original plan.
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